Information

Killing enveloped viruses with soap


  1. Unlike non-enveloped viruses, enveloped viruses can be killed with soap, alcohol, etc. Why?

  2. Why does just having an envelope make it susceptible to soap and alcohol?


Soap molecules are amphiphilic. This means they have parts which are hydrophilic (water-loving, or "polar") and parts which are hydrophobic (water-avoiding, or "non-polar").

Fat molecules are non-polar. They avoid water. This is why a mixture of oil and water will separate into layers. In this mix, oil molecules prefer to hang around other oil molecules, and water molecules prefer to hang around other water molecules. Soap "likes" both oil and water, so it can be used for cleaning, by helping dissolve this mixture. (For a similar reason, this is why vinegar is used to dissolve or emulsify oil in salad dressings.)

The coat of an enveloped virus is made up of layer of phospholipid molecules and proteins. Phospholipid molecules are similar to detergents, made up of polar and non-polar ends. These lipids arrange themselves into a two-layered sandwich called a "bilayer". The polar ends of this sandwich are the "bread", while the fatty non-polar ends are the "filling".

Detergents can help disturb this by pulling or dissolving out phospholipids from the virus coat to form micelles, tiny bubbles of fat and soap that can be washed away. This puts holes in the virus coat and helps dissolve it.

The insides of the enveloped virus particle cannot infect directly and must rely on its envelope to get into and infect a cell, so breaking down the coat inactivates (or "kills") the virus.

Alcohols are also amphiphilic. There are many different alcohols, but they all have a hydroxy group at one end, which is polar, and a saturated or partially-saturated carbon chain on the other end, which is non-polar. Like detergents, this property allows an alcohol - at a sufficient concentration - to disturb and break down the virus envelope phospholipid bilayer, inactivating it.

Non-enveloped viruses lack this phospholipid bilayer coating and are instead protected by a protein capsid. The proteins in a capsid will not dissolve with detergents, but they can be attacked with other disinfectants that chemically denature the proteins. Examples of such disinfectants are chlorine (bleach), iodine, peroxides, etc.

Just as soap can put holes into the phospholipid coating around enveloped viruses, destabilizing them, denaturing agents change the structure of proteins that protect non-enveloped viruses, also destabilizing the capsid. If the capsid proteins are damaged sufficiently, the virus particle is not able to infect a cell and so is deactivated.


Why soap is preferable to bleach in the fight against coronavirus

For nearly 5,000 years, humans have concocted cleaning products – yet the simple combination of soap and water remains one of the strongest weapons against infectious diseases, including the novel coronavirus. Even so, when outbreaks like COVID-19 occur and panic sets in, people rush to buy all sorts of chemical cleaners, many of which are unnecessary or ineffective against viruses.

Foam hand sanitisers are disappearing from store shelves, even though many lack the necessary amount of alcohol—at least 60 percent by volume—to kill viruses. In countries hardest hit by the novel coronavirus, photos show crews in hazmat suits spraying bleach solutions along public sidewalks or inside office buildings. Experts are dubious, however, of whether that’s necessary to neutralise the spread of the coronavirus.

Using bleach “is like using a bludgeon to swat a fly,” says Jane Greatorex, a virologist at Cambridge University. It can also corrode metal and lead to other respiratory health problems if inhaled too much over time.

“With bleach, if you put it on a surface with a lot of dirt, that [dirt] will eat up the bleach,” says Lisa Casanova, an environmental health scientist at Georgia State University. She and other experts instead recommend using milder acidic soaps, like dish soap, to easily sanitise a surface indoors and outdoors.

To fully understand why health officials keep coming back to soap, it helps to know how the coronavirus exists outside the body, and what early research is saying about how long the virus can linger on common surfaces.


The Global Handwashing Partnership

Soap is one of our most effective defences against invisible pathogens
At the molecular level, soap breaks things apart. At the level of society, it helps hold everything together. It probably began with an accident thousands of years ago. According to one legend, rain washed the fat and ash from frequent animal sacrifices into a nearby river, where they formed a lather with a remarkable ability to clean skin and clothes. Perhaps the inspiration had a vegetal origin in the frothy solutions produced by boiling or mashing certain plants. However it happened, the ancient discovery of soap altered human history. Although our ancestors could not have foreseen it, soap would ultimately become one of our most effective defences against invisible pathogens.

Soap is gentle and soothing – and can be extremely destructive for micro-organisms
People typically think of soap as gentle and soothing, but from the perspective of microorganisms, it is often extremely destructive. A drop of ordinary soap diluted in water is sufficient to rupture and kill many types of bacteria and viruses, including the new Coronavirus that is currently circling the globe. The secret to soap’s impressive might is its hybrid structure.

Soap is made of pin-shaped molecules, each of which has a hydrophilic head — it readily bonds with water — and a hydrophobic tail, which shuns water and prefers to link up with oils and fats. These molecules, when suspended in water, alternately float about as solitary units, interact with other molecules in the solution and assemble themselves into little bubbles called micelles, with heads pointing outward and tails tucked inside.

Some bacteria and viruses have lipid membranes that resemble double-layered micelles with two bands of hydrophobic tails sandwiched between two rings of hydrophilic heads. These membranes are studded with important proteins that allow viruses to infect cells and perform vital tasks that keep bacteria alive. Pathogens wrapped in lipid membranes include Coronaviruses, HIV, the viruses that cause hepatitis B and C, herpes, Ebola, Zika, dengue, and numerous bacteria that attack the intestines and respiratory tract.

When you wash your hands with soap and water, you surround any microorganisms on your skin with soap molecules. The hydrophobic tails of the free-floating soap molecules attempt to evade water in the process, they wedge themselves into the lipid envelopes of certain microbes and viruses, prying them apart.

“They act like crowbars and destabilize the whole system,” said Prof. Pall Thordarson, acting head of chemistry at the University of New South Wales. Essential proteins spill from the ruptured membranes into the surrounding water, killing the bacteria and rendering the viruses useless.

How Soap Works
Washing with soap and water is an effective way to destroy and dislodge many microbes, including the new Coronavirus. For more about the how the virus affects the body, see How Coronavirus Hijacks Your Cells.

Photo Credit: Jonathan Corum and Ferris Jabr

In tandem, some soap molecules disrupt the chemical bonds that allow bacteria, viruses and grime to stick to surfaces, lifting them off the skin. Micelles can also form around particles of dirt and fragments of viruses and bacteria, suspending them in floating cages. When you rinse your hands, all the microorganisms that have been damaged, trapped and killed by soap molecules are washed away.

On the whole, hand sanitisers are not as reliable as soap
Sanitisers with at least 60 percent ethanol do act similarly, defeating bacteria and viruses by destabilizing their lipid membranes. But they cannot easily remove microorganisms from the skin. There are also viruses that do not depend on lipid membranes to infect cells, as well as bacteria that protect their delicate membranes with sturdy shields of protein and sugar. Examples include bacteria that can cause meningitis, pneumonia, diarrhoea and skin infections, as well as the hepatitis A virus, poliovirus, rhinoviruses and adenoviruses (frequent causes of the common cold).

These more resilient microbes are generally less susceptible to the chemical onslaught of ethanol and soap. But vigorous scrubbing with soap and water can still expunge these microbes from the skin, which is partly why hand-washing is more effective than sanitizer. Alcohol-based sanitizer is a good backup when soap and water are not accessible.

Soap in water remains one of our most valuable medical interventions
In an age of robotic surgery and gene therapy, it is all the more wondrous that a bit of soap in water, an ancient and fundamentally unaltered recipe, remains one of our most valuable medical interventions. Throughout the course of a day, we pick up all sorts of viruses and microorganisms from the objects and people in the environment.

When we absentmindedly touch our eyes, nose and mouth – a habit, one study suggests, that recurs as often as every two and a half minutes — we offer potentially dangerous microbes a portal to our internal organs.

As a foundation of everyday hygiene, hand-washing was broadly adopted relatively recently. In the 1840s Dr. Ignaz Semmelweis, a Hungarian physician, discovered that if doctors washed their hands, far fewer women died after childbirth. At the time, microbes were not widely recognized as vectors of disease, and many doctors ridiculed the notion that a lack of personal cleanliness could be responsible for their patients’ deaths. Ostracized by his colleagues, Dr. Semmelweis was eventually committed to an asylum, where he was severely beaten by guards and died from infected wounds.

Florence Nightingale, the English nurse and statistician, also promoted hand-washing in the mid-1800s, but it was not until the 1980s that the Centers for Disease Control and Prevention issued the world’s first nationally endorsed hand hygiene guidelines.

Washing with soap and water is one of the key public health practices that can significantly slow the rate of a pandemic and limit the number of infections, preventing a disastrous overburdening of hospitals and clinics.

But the technique works only if everyone washes their hands frequently and thoroughly:
Work up a good lather, scrub your palms and the back of your hands, interlace your fingers, rub your fingertips against your palms, and twist a soapy fist around your thumbs. Or as the Canadian health officer Bonnie Henry said recently:

Wash your hands like you’ve been chopping jalapeños and you need to change your contacts.”

Even people who are relatively young and healthy should regularly wash their hands, especially during a pandemic, because they can spread the disease to those who are more vulnerable.

Soap is more than a personal protectant when used properly, it becomes part of a communal safety net. At the molecular level, soap works by breaking things apart, but at the level of society, it helps hold everything together.

Remember this the next time you have the impulse to bypass the sink: Other people’s lives are in your hands.


The action of three antiseptics/disinfectants against enveloped and non-enveloped viruses

The antiviral action of chloroxylenol, benzalkonium chloride and cetrimide/chlorhexidine was assessed against a range of enveloped and non-enveloped human viruses using a suspension test method. Viral suspensions of 10(6)-10(7) pfu/TCID50 or sfu were prepared in each of the antiseptic/disinfectant solutions in the presence of a bovine serum/yeast extract mixture to simulate 'dirty conditions'. During incubation, aliquots were removed at predetermined timepoints up to 10 min to assess the kinetics of inactivation. Results indicate that all products were effective in inactivating the enveloped viruses herpes simplex virus type 1 and human immunodeficiency virus type 1, whilst being ineffective in inactivating human coronavirus, also enveloped, and the non-enveloped viruses. The exception to this was the benzalkonium chloride-based product (Dettol Hospital Concentrate) which was active against the non-enveloped human coxsackie virus. Four antiseptic/disinfectant solutions with chloroxylenol, benzalkonium chloride, cetrimide/chlorhexidine and povidone-iodine were also assessed for antiviral effect against human immunodeficiency virus in the presence of whole human blood. All four solutions proved to be effective within 1 min despite the cytotoxic nature of the compounds to the detection system.


Yes, Soap Is Superior To Sanitizer. But Where’s The Evidence?

Scientific studies suggest that good hand hygiene helps stop the spread of Coronavirus, and the Centers for Disease Control says that washing with soap and water is the best way to get rid of germs. Using an alcohol-based sanitizer should be your second choice, but is using it really worse than handwashing?

When the media first covered the science behind why soap is effective, they jumped straight to how it "absolutely annihilates" SARS-CoV-2. Briefly, soap contains 'amphiphile' molecules with fat-loving ends, which are similar to those that make up the membrane — a double-layered 'envelope' — that surrounds a virus particle. The alcohol molecules in sanitizers are also amphiphiles, but their activity is slower than the 30 seconds that soap needs to work its magic.

As Palli Thordarson, chemistry professor at the University of New South Wales in Sydney, explained, "the virus is a self-assembled nanoparticle in which the weakest link is the lipid (fatty) bilayer. Soap dissolves the fat membrane and the virus falls apart like a house of cards and dies."

But that's an explanation for how soap destroys enveloped viruses — it's not evidence that handwashing is best for good hygiene. That said, washing in a sink to get clean hands does have several advantages over using a sanitizer.

One benefit of soap is that mechanical friction from scrubbing produces a foam that can cover a large surface area and gets into every nook and cranny of your skin (be warned that scrubbing too hard can leave you with cracked skin and let germs get through gaps in the body's first line of defence against invaders).

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The process of handwashing provides another benefit to using soap and water. A Japanese study showed that in order to kill the influenza A virus, alcohol-based sanitizers needed to be in contact with virus particles for four minutes (this is partly because the flu virus is protected from ethanol by a thin layer of mucous). And yet the hand sanitizer wasn't even as effective as washing with water alone, which inactivated the virus within 30 seconds.

Handwashing also removes debris. While sanitizer might kill germs, it leaves the dead microbes on your skin. As a systematic review of the germs transmitted during food preparation noted, "Water and soap appear to be more effective than waterless products for removal of soil and microorganisms from hands."

Alcohol-based sanitizers also have more potentially harmful effects on health. Besides being a fire hazard, alcohol is toxic when absorbed through the skin and children can accidentally drink hand rub containing unlisted ingredients like methanol, which has led to fatal cases of poisoning.

The active agents in soap are salts of fatty acids, such as sodium stearate, and special ingredients aren't necessary to fight microbes. According to a study in Pakistan, a plain bar of soap is just as effective as antibacterial bars at preventing pneumonia in children: both reduced infections by half.

Taken together, after weighing the numerous costs and benefits, one review concluded that "soap and water is superior to sanitizer". The conclusion wasn't based on hand sanitizers being better at destroying enveloped viruses, however, but "various factors, such as elimination of a wider spectrum of pathogens and chemicals, and removal of bioburden on soiled hands."

So what about soap being better than sanitizer at killing Coronavirus? There isn't much proof to support that claim, although it hasn't been disproven either. The most direct comparison of the two hygiene interventions comes from a study by German microbiologists, who showed that antimicrobial soaps and ethanol-based sanitizers could both inactivate over 99% of enveloped viruses, including Vaccinia (a relative of smallpox). The study didn't test respiratory viruses.

In terms of the efficacy of soap versus sanitizer for viruses closer to SARS-CoV-2, there's indirect evidence from a study of office environments in Finland, which found that self-reported respiratory illness was reduced for participants who frequently washed their hands, but not for those who used a hand rub containing 80% ethanol.

Overall, as an unpublished 2020 update to another systematic review of the scientific literature concluded, "There were too few trials comparing different types of hand hygiene interventions to be certain of any differences between soap and water, alcohol-based hand sanitizers, or other types of interventions."

Assuming that soap is the best way to kill Coronavirus, there are many reasons why that isn't reflected in published studies. Using handwashing facilities is less convenient than using a hand sanitizer, for example, so you might be more likely to stick to sanitizer because it's easy to use. Interestingly, an experiment led by food safety expert Kristen Gibson at the University of Arkansas showed that participants spent almost 5 seconds longer handwashing with a gel-based soap compared to a foaming soap.

Remembering to follow a less-effective method to maintain hand hygiene is better than forgetting altogether, especially when health interventions often suffer from drops in 'compliance' over time. That's why the CDC is still happy to recommend using hand sanitizers if soap and water are not available.

So while there's a likely explanation for how soap destroys enveloped viruses like SARS-CoV-2, there isn't much specific evidence to support the suggestion that it's more effective than hand sanitizer. And yet when it comes to good hygiene, despite the lack of evidence, it's probably better to be safe than sorry.

Whenever possible, you should thoroughly and frequently wash your hands with soap.


Conclusion

We herein showed that viruses persisted for days or even weeks on dry hydrophobic surfaces. The pattern of resistance of viruses toward drying, as illustrated in the model of CVB4, was not due to the heterogeneity of viral populations, as suggested by the results of iterative drying. Moreover, media compositions and component concentrations clearly played a role when virus suspensions were exposed to drying. The results of our study suggest that a subsequent increase in solute concentrations in droplets modulated the viability of viruses toward drying. Since the compositions of media play a role in the viability of viruses exposed to drying, the persistence of viruses in natural media (clinical or environmental), instead of defined media, need to be investigated. Further studies will be directed towards this line of investigation in our laboratory.


Chemical Disinfectants

In the healthcare setting, &ldquoalcohol&rdquo refers to two water-soluble chemical compounds&mdashethyl alcohol and isopropyl alcohol&mdashthat have generally underrated germicidal characteristics 482 . FDA has not cleared any liquid chemical sterilant or high-level disinfectant with alcohol as the main active ingredient. These alcohols are rapidly bactericidal rather than bacteriostatic against vegetative forms of bacteria they also are tuberculocidal, fungicidal, and virucidal but do not destroy bacterial spores. Their cidal activity drops sharply when diluted below 50% concentration, and the optimum bactericidal concentration is 60%&ndash90% solutions in water (volume/volume) 483, 484 .

Mode of Action.

The most feasible explanation for the antimicrobial action of alcohol is denaturation of proteins. This mechanism is supported by the observation that absolute ethyl alcohol, a dehydrating agent, is less bactericidal than mixtures of alcohol and water because proteins are denatured more quickly in the presence of water 484, 485 . Protein denaturation also is consistent with observations that alcohol destroys the dehydrogenases of Escherichia coli 486 , and that ethyl alcohol increases the lag phase of Enterobacter aerogenes 487 and that the lag phase effect could be reversed by adding certain amino acids. The bacteriostatic action was believed caused by inhibition of the production of metabolites essential for rapid cell division.

Microbicidal Activity.

Methyl alcohol (methanol) has the weakest bactericidal action of the alcohols and thus seldom is used in healthcare 488 . The bactericidal activity of various concentrations of ethyl alcohol (ethanol) was examined against a variety of microorganisms in exposure periods ranging from 10 seconds to 1 hour 483 . Pseudomonas aeruginosa was killed in 10 seconds by all concentrations of ethanol from 30% to 100% (v/v), and Serratia marcescens, E, coli and Salmonella typhosa were killed in 10 seconds by all concentrations of ethanol from 40% to 100%. The gram-positive organisms Staphylococcus aureus and Streptococcus pyogenes were slightly more resistant, being killed in 10 seconds by ethyl alcohol concentrations of 60%&ndash95%. Isopropyl alcohol (isopropanol) was slightly more bactericidal than ethyl alcohol for E. coli and S. aureus 489 .

Ethyl alcohol, at concentrations of 60%&ndash80%, is a potent virucidal agent inactivating all of the lipophilic viruses (e.g., herpes, vaccinia, and influenza virus) and many hydrophilic viruses (e.g., adenovirus, enterovirus, rhinovirus, and rotaviruses but not hepatitis A virus (HAV) 58 or poliovirus) 49 . Isopropyl alcohol is not active against the nonlipid enteroviruses but is fully active against the lipid viruses 72 . Studies also have demonstrated the ability of ethyl and isopropyl alcohol to inactivate the hepatitis B virus(HBV) 224, 225 and the herpes virus, 490 and ethyl alcohol to inactivate human immunodeficiency virus (HIV) 227 , rotavirus, echovirus, and astrovirus 491 .

In tests of the effect of ethyl alcohol against M. tuberculosis, 95% ethanol killed the tubercle bacilli in sputum or water suspension within 15 seconds 492 . In 1964, Spaulding stated that alcohols were the germicide of choice for tuberculocidal activity, and they should be the standard by which all other tuberculocides are compared. For example, he compared the tuberculocidal activity of iodophor (450 ppm), a substituted phenol (3%), and isopropanol (70%/volume) using the mucin-loop test (10 6 M. tuberculosis per loop) and determined the contact times needed for complete destruction were 120&ndash180 minutes, 45&ndash60 minutes, and 5 minutes, respectively. The mucin-loop test is a severe test developed to produce long survival times. Thus, these figures should not be extrapolated to the exposure times needed when these germicides are used on medical or surgical material 482 .

Ethyl alcohol (70%) was the most effective concentration for killing the tissue phase of Cryptococcus neoformans, Blastomyces dermatitidis, Coccidioides immitis, and Histoplasma capsulatum and the culture phases of the latter three organisms aerosolized onto various surfaces. The culture phase was more resistant to the action of ethyl alcohol and required about 20 minutes to disinfect the contaminated surface, compared with <1 minute for the tissue phase 493, 494 .

Isopropyl alcohol (20%) is effective in killing the cysts of Acanthamoeba culbertsoni (560) as are chlorhexidine, hydrogen peroxide, and thimerosal 496 .

Alcohols are not recommended for sterilizing medical and surgical materials principally because they lack sporicidal action and they cannot penetrate protein-rich materials. Fatal postoperative wound infections with Clostridium have occurred when alcohols were used to sterilize surgical instruments contaminated with bacterial spores 497 . Alcohols have been used effectively to disinfect oral and rectal thermometers 498, 499 , hospital pagers 500 , scissors 501 , and stethoscopes 502 . Alcohols have been used to disinfect fiberoptic endoscopes 503, 504 but failure of this disinfectant have lead to infection 280, 505 . Alcohol towelettes have been used for years to disinfect small surfaces such as rubber stoppers of multiple-dose medication vials or vaccine bottles. Furthermore, alcohol occasionally is used to disinfect external surfaces of equipment (e.g., stethoscopes, ventilators, manual ventilation bags) 506 , CPR manikins 507 , ultrasound instruments 508 or medication preparation areas. Two studies demonstrated the effectiveness of 70% isopropyl alcohol to disinfect reusable transducer heads in a controlled environment 509, 510 . In contrast, three bloodstream infection outbreaks have been described when alcohol was used to disinfect transducer heads in an intensive-care setting 511 .

The documented shortcomings of alcohols on equipment are that they damage the shellac mountings of lensed instruments, tend to swell and harden rubber and certain plastic tubing after prolonged and repeated use, bleach rubber and plastic tiles 482 and damage tonometer tips (by deterioration of the glue) after the equivalent of 1 working year of routine use 512 . Tonometer biprisms soaked in alcohol for 4 days developed rough front surfaces that potentially could cause corneal damage this appeared to be caused by weakening of the cementing substances used to fabricate the biprisms 513 . Corneal opacification has been reported when tonometer tips were swabbed with alcohol immediately before measurement of intraocular pressure 514 . Alcohols are flammable and consequently must be stored in a cool, well-ventilated area. They also evaporate rapidly, making extended exposure time difficult to achieve unless the items are immersed.

Chlorine and Chlorine Compounds

Overview.

Hypochlorites, the most widely used of the chlorine disinfectants, are available as liquid (e.g., sodium hypochlorite) or solid (e.g., calcium hypochlorite). The most prevalent chlorine products in the United States are aqueous solutions of 5.25%&ndash6.15% sodium hypochlorite (see glossary), usually called household bleach. They have a broad spectrum of antimicrobial activity, do not leave toxic residues, are unaffected by water hardness, are inexpensive and fast acting 328 , remove dried or fixed organisms and biofilms from surfaces 465 , and have a low incidence of serious toxicity 515-517 . Sodium hypochlorite at the concentration used in household bleach (5.25-6.15%) can produce ocular irritation or oropharyngeal, esophageal, and gastric burns 318, 518-522 . Other disadvantages of hypochlorites include corrosiveness to metals in high concentrations (>500 ppm), inactivation by organic matter, discoloring or &ldquobleaching&rdquo of fabrics, release of toxic chlorine gas when mixed with ammonia or acid (e.g., household cleaning agents) 523-525 , and relative stability 327 . The microbicidal activity of chlorine is attributed largely to undissociated hypochlorous acid (HOCl). The dissociation of HOCI to the less microbicidal form (hypochlorite ion OCl ‑ ) depends on pH. The disinfecting efficacy of chlorine decreases with an increase in pH that parallels the conversion of undissociated HOCI to OCl ‑ 329, 526 . A potential hazard is production of the carcinogen bis(chloromethyl) ether when hypochlorite solutions contact formaldehyde 527 and the production of the animal carcinogen trihalomethane when hot water is hyperchlorinated 528 . After reviewing environmental fate and ecologic data, EPA has determined the currently registered uses of hypochlorites will not result in unreasonable adverse effects to the environment 529 .

Alternative compounds that release chlorine and are used in the health-care setting include demand-release chlorine dioxide, sodium dichloroisocyanurate, and chloramine-T. The advantage of these compounds over the hypochlorites is that they retain chlorine longer and so exert a more prolonged bactericidal effect. Sodium dichloroisocyanurate tablets are stable, and for two reasons, the microbicidal activity of solutions prepared from sodium dichloroisocyanurate tablets might be greater than that of sodium hypochlorite solutions containing the same total available chlorine. First, with sodium dichloroisocyanurate, only 50% of the total available chlorine is free (HOCl and OCl &ndash ), whereas the remainder is combined (monochloroisocyanurate or dichloroisocyanurate), and as free available chlorine is used up, the latter is released to restore the equilibrium. Second, solutions of sodium dichloroisocyanurate are acidic, whereas sodium hypochlorite solutions are alkaline, and the more microbicidal type of chlorine (HOCl) is believed to predominate 530-533 . Chlorine dioxide-based disinfectants are prepared fresh as required by mixing the two components (base solution [citric acid with preservatives and corrosion inhibitors] and the activator solution [sodium chlorite]). In vitro suspension tests showed that solutions containing about 140 ppm chlorine dioxide achieved a reduction factor exceeding 10 6 of S. aureus in 1 minute and of Bacillus atrophaeus spores in 2.5 minutes in the presence of 3 g/L bovine albumin. The potential for damaging equipment requires consideration because long-term use can damage the outer plastic coat of the insertion tube 534 . In another study, chlorine dioxide solutions at either 600 ppm or 30 ppm killed Mycobacterium avium-intracellulare within 60 seconds after contact but contamination by organic material significantly affected the microbicidal properties 535 .

The microbicidal activity of a new disinfectant, &ldquosuperoxidized water,&rdquo has been examined The concept of electrolyzing saline to create a disinfectant or antiseptics is appealing because the basic materials of saline and electricity are inexpensive and the end product (i.e., water) does not damage the environment. The main products of this water are hypochlorous acid (e.g., at a concentration of about 144 mg/L) and chlorine. As with any germicide, the antimicrobial activity of superoxidized water is strongly affected by the concentration of the active ingredient (available free chlorine) 536 . One manufacturer generates the disinfectant at the point of use by passing a saline solution over coated titanium electrodes at 9 amps. The product generated has a pH of 5.0&ndash6.5 and an oxidation-reduction potential (redox) of >950 mV. Although superoxidized water is intended to be generated fresh at the point of use, when tested under clean conditions the disinfectant was effective within 5 minutes when 48 hours old 537 . Unfortunately, the equipment required to produce the product can be expensive because parameters such as pH, current, and redox potential must be closely monitored. The solution is nontoxic to biologic tissues. Although the United Kingdom manufacturer claims the solution is noncorrosive and nondamaging to endoscopes and processing equipment, one flexible endoscope manufacturer (Olympus Key-Med, United Kingdom) has voided the warranty on the endoscopes if superoxidized water is used to disinfect them 538 . As with any germicide formulation, the user should check with the device manufacturer for compatibility with the germicide. Additional studies are needed to determine whether this solution could be used as an alternative to other disinfectants or antiseptics for hand washing, skin antisepsis, room cleaning, or equipment disinfection (e.g., endoscopes, dialyzers) 400, 539, 540 . In October 2002, the FDA cleared superoxidized water as a high-level disinfectant (FDA, personal communication, September 18, 2002).

Mode of Action.

The exact mechanism by which free chlorine destroys microorganisms has not been elucidated. Inactivation by chlorine can result from a number of factors: oxidation of sulfhydryl enzymes and amino acids ring chlorination of amino acids loss of intracellular contents decreased uptake of nutrients inhibition of protein synthesis decreased oxygen uptake oxidation of respiratory components decreased adenosine triphosphate production breaks in DNA and depressed DNA synthesis 329, 347 . The actual microbicidal mechanism of chlorine might involve a combination of these factors or the effect of chlorine on critical sites 347 .

Microbicidal Activity.

Low concentrations of free available chlorine (e.g., HOCl, OCl &ndash , and elemental chlorine-Cl2) have a biocidal effect on mycoplasma (25 ppm) and vegetative bacteria (<5 ppm) in seconds in the absence of an organic load 329, 418 . Higher concentrations (1,000 ppm) of chlorine are required to kill M. tuberculosis using the Association of Official Analytical Chemists (AOAC) tuberculocidal test 73 . A concentration of 100 ppm will kill &ge99.9% of B. atrophaeus spores within 5 minutes 541, 542 and destroy mycotic agents in <1 hour 329 . Acidified bleach and regular bleach (5,000 ppm chlorine) can inactivate 10 6 Clostridium difficile spores in &le10 minutes 262 . One study reported that 25 different viruses were inactivated in 10 minutes with 200 ppm available chlorine 72 . Several studies have demonstrated the effectiveness of diluted sodium hypochlorite and other disinfectants to inactivate HIV 61 . Chlorine (500 ppm) showed inhibition of Candida after 30 seconds of exposure 54 . In experiments using the AOAC Use-Dilution Method, 100 ppm of free chlorine killed 10 6 &ndash10 7 S. aureus, Salmonella choleraesuis, and P. aeruginosa in <10 minutes 327 . Because household bleach contains 5.25%&ndash6.15% sodium hypochlorite, or 52,500&ndash61,500 ppm available chlorine, a 1:1,000 dilution provides about 53&ndash62 ppm available chlorine, and a 1:10 dilution of household bleach provides about 5250&ndash6150 ppm.

Data are available for chlorine dioxide that support manufacturers&rsquo bactericidal, fungicidal, sporicidal, tuberculocidal, and virucidal label claims 543-546 . A chlorine dioxide generator has been shown effective for decontaminating flexible endoscopes 534 but it is not currently FDA-cleared for use as a high-level disinfectant 85 . Chlorine dioxide can be produced by mixing solutions, such as a solution of chlorine with a solution of sodium chlorite 329 . In 1986, a chlorine dioxide product was voluntarily removed from the market when its use caused leakage of cellulose-based dialyzer membranes, which allowed bacteria to migrate from the dialysis fluid side of the dialyzer to the blood side 547 .

Sodium dichloroisocyanurate at 2,500 ppm available chlorine is effective against bacteria in the presence of up to 20% plasma, compared with 10% plasma for sodium hypochlorite at 2,500 ppm 548 .

&ldquoSuperoxidized water&rdquo has been tested against bacteria, mycobacteria, viruses, fungi, and spores 537, 539, 549 . Freshly generated superoxidized water is rapidly effective (<2 minutes) in achieving a 5-log10 reduction of pathogenic microorganisms (i.e., M. tuberculosis, M. chelonae, poliovirus, HIV, multidrug-resistant S. aureus, E. coli, Candida albicans, Enterococcus faecalis, P. aeruginosa) in the absence of organic loading. However, the biocidal activity of this disinfectant decreased substantially in the presence of organic material (e.g., 5% horse serum) 537, 549, 550 . No bacteria or viruses were detected on artificially contaminated endoscopes after a 5-minute exposure to superoxidized water 551 and HBV-DNA was not detected from any endoscope experimentally contaminated with HBV-positive mixed sera after a disinfectant exposure time of 7 minutes 552 .

Hypochlorites are widely used in healthcare facilities in a variety of settings. 328 Inorganic chlorine solution is used for disinfecting tonometer heads 188 and for spot-disinfection of countertops and floors. A 1:10&ndash1:100 dilution of 5.25%&ndash6.15% sodium hypochlorite (i.e., household bleach) 22, 228, 553, 554 or an EPA-registered tuberculocidal disinfectant 17 has been recommended for decontaminating blood spills. For small spills of blood (i.e., drops of blood) on noncritical surfaces, the area can be disinfected with a 1:100 dilution of 5.25%-6.15% sodium hypochlorite or an EPA-registered tuberculocidal disinfectant. Because hypochlorites and other germicides are substantially inactivated in the presence of blood 63, 548, 555, 556 , large spills of blood require that the surface be cleaned before an EPA-registered disinfectant or a 1:10 (final concentration) solution of household bleach is applied 557 . If a sharps injury is possible, the surface initially should be decontaminated 69, 318 , then cleaned and disinfected (1:10 final concentration) 63 . Extreme care always should be taken to prevent percutaneous injury. At least 500 ppm available chlorine for 10 minutes is recommended for decontaminating CPR training manikins 558 . Full-strength bleach has been recommended for self-disinfection of needles and syringes used for illicit-drug injection when needle-exchange programs are not available. The difference in the recommended concentrations of bleach reflects the difficulty of cleaning the interior of needles and syringes and the use of needles and syringes for parenteral injection 559 . Clinicians should not alter their use of chlorine on environmental surfaces on the basis of testing methodologies that do not simulate actual disinfection practices 560, 561 . Other uses in healthcare include as an irrigating agent in endodontic treatment 562 and as a disinfectant for manikins, laundry, dental appliances, hydrotherapy tanks 23, 41 , regulated medical waste before disposal 328 , and the water distribution system in hemodialysis centers and hemodialysis machines 563 .

Chlorine long has been used as the disinfectant in water treatment. Hyperchlorination of a Legionella-contaminated hospital water system 23 resulted in a dramatic decrease (from 30% to 1.5%) in the isolation of L. pneumophila from water outlets and a cessation of healthcare-associated Legionnaires&rsquo disease in an affected unit 528, 564 . Water disinfection with monochloramine by municipal water-treatment plants substantially reduced the risk for healthcare&ndashassociated Legionnaires disease 565, 566 . Chlorine dioxide also has been used to control Legionella in a hospital water supply. 567 Chloramine T 568 and hypochlorites 41 have been used to disinfect hydrotherapy equipment.

Hypochlorite solutions in tap water at a pH >8 stored at room temperature (23°C) in closed, opaque plastic containers can lose up to 40%&ndash50% of their free available chlorine level over 1 month. Thus, if a user wished to have a solution containing 500 ppm of available chlorine at day 30, he or she should prepare a solution containing 1,000 ppm of chlorine at time 0. Sodium hypochlorite solution does not decompose after 30 days when stored in a closed brown bottle 327 .

The use of powders, composed of a mixture of a chlorine-releasing agent with highly absorbent resin, for disinfecting spills of body fluids has been evaluated by laboratory tests and hospital ward trials. The inclusion of acrylic resin particles in formulations markedly increases the volume of fluid that can be soaked up because the resin can absorb 200&ndash300 times its own weight of fluid, depending on the fluid consistency. When experimental formulations containing 1%, 5%, and 10% available chlorine were evaluated by a standardized surface test, those containing 10% demonstrated bactericidal activity. One problem with chlorine-releasing granules is that they can generate chlorine fumes when applied to urine 569 .

Formaldehyde

Overview.

Formaldehyde is used as a disinfectant and sterilant in both its liquid and gaseous states. Liquid formaldehyde will be considered briefly in this section, and the gaseous form is reviewed elsewhere 570 . Formaldehyde is sold and used principally as a water-based solution called formalin, which is 37% formaldehyde by weight. The aqueous solution is a bactericide, tuberculocide, fungicide, virucide and sporicide 72, 82, 571-573 . OSHA indicated that formaldehyde should be handled in the workplace as a potential carcinogen and set an employee exposure standard for formaldehyde that limits an 8-hour time-weighted average exposure concentration of 0.75 ppm 574, 575 . The standard includes a second permissible exposure limit in the form of a short-term exposure limit (STEL) of 2 ppm that is the maximum exposure allowed during a 15-minute period 576 . Ingestion of formaldehyde can be fatal, and long-term exposure to low levels in the air or on the skin can cause asthma-like respiratory problems and skin irritation, such as dermatitis and itching. For these reasons, employees should have limited direct contact with formaldehyde, and these considerations limit its role in sterilization and disinfection processes. Key provisions of the OSHA standard that protects workers from exposure to formaldehyde appear in Title 29 of the Code of Federal Regulations (CFR) Part 1910.1048 (and equivalent regulations in states with OSHA-approved state plans) 577 .

Mode of Action.

Formaldehyde inactivates microorganisms by alkylating the amino and sulfhydral groups of proteins and ring nitrogen atoms of purine bases 376 .

Microbicidal Activity.

Varying concentrations of aqueous formaldehyde solutions destroy a wide range of microorganisms. Inactivation of poliovirus in 10 minutes required an 8% concentration of formalin, but all other viruses tested were inactivated with 2% formalin 72 . Four percent formaldehyde is a tuberculocidal agent, inactivating 10 4 M. tuberculosis in 2 minutes 82 , and 2.5% formaldehyde inactivated about 10 7 Salmonella Typhi in 10 minutes in the presence of organic matter 572 . The sporicidal action of formaldehyde was slower than that of glutaraldehyde in comparative tests with 4% aqueous formaldehyde and 2% glutaraldehyde against the spores of B. anthracis 82 . The formaldehyde solution required 2 hours of contact to achieve an inactivation factor of 10 4 , whereas glutaraldehyde required only 15 minutes.

Although formaldehyde-alcohol is a chemical sterilant and formaldehyde is a high-level disinfectant, the health-care uses of formaldehyde are limited by its irritating fumes and its pungent odor even at very low levels (<1 ppm). For these reasons and others&mdashsuch as its role as a suspected human carcinogen linked to nasal cancer and lung cancer 578 , this germicide is excluded from Table 1. When it is used, , direct exposure to employees generally is limited however, excessive exposures to formaldehyde have been documented for employees of renal transplant units 574, 579 , and students in a gross anatomy laboratory 580 . Formaldehyde is used in the health-care setting to prepare viral vaccines (e.g., poliovirus and influenza) as an embalming agent and to preserve anatomic specimens and historically has been used to sterilize surgical instruments, especially when mixed with ethanol. A 1997 survey found that formaldehyde was used for reprocessing hemodialyzers by 34% of U.S. hemodialysis centers&mdasha 60% decrease from 1983 249, 581 . If used at room temperature, a concentration of 4% with a minimum exposure of 24 hours is required to disinfect disposable hemodialyzers reused on the same patient 582, 583 . Aqueous formaldehyde solutions (1%&ndash2%) also have been used to disinfect the internal fluid pathways of dialysis machines 583 . To minimize a potential health hazard to dialysis patients, the dialysis equipment must be thoroughly rinsed and tested for residual formaldehyde before use.

Paraformaldehyde, a solid polymer of formaldehyde, can be vaporized by heat for the gaseous decontamination of laminar flow biologic safety cabinets when maintenance work or filter changes require access to the sealed portion of the cabinet.

Glutaraldehyde

Overview.

Glutaraldehyde is a saturated dialdehyde that has gained wide acceptance as a high-level disinfectant and chemical sterilant 107 . Aqueous solutions of glutaraldehyde are acidic and generally in this state are not sporicidal. Only when the solution is &ldquoactivated&rdquo (made alkaline) by use of alkalinating agents to pH 7.5&ndash8.5 does the solution become sporicidal. Once activated, these solutions have a shelf-life of minimally 14 days because of the polymerization of the glutaraldehyde molecules at alkaline pH levels. This polymerization blocks the active sites (aldehyde groups) of the glutaraldehyde molecules that are responsible for its biocidal activity.

Novel glutaraldehyde formulations (e.g., glutaraldehyde-phenol-sodium phenate, potentiated acid glutaraldehyde, stabilized alkaline glutaraldehyde) produced in the past 30 years have overcome the problem of rapid loss of activity (e.g., use-life 28&ndash30 days) while generally maintaining excellent microbicidal activity 584-588 . However, antimicrobial activity depends not only on age but also on use conditions, such as dilution and organic stress. Manufacturers&rsquo literature for these preparations suggests the neutral or alkaline glutaraldehydes possess microbicidal and anticorrosion properties superior to those of acid glutaraldehydes, and a few published reports substantiate these claims 542, 589, 590 . However, two studies found no difference in the microbicidal activity of alkaline and acid glutaraldehydes 73, 591 . The use of glutaraldehyde-based solutions in health-care facilities is widespread because of their advantages, including excellent biocidal properties activity in the presence of organic matter (20% bovine serum) and noncorrosive action to endoscopic equipment, thermometers, rubber, or plastic equipment (Tables 4 and 5).

Mode of Action.

The biocidal activity of glutaraldehyde results from its alkylation of sulfhydryl, hydroxyl, carboxyl, and amino groups of microorganisms, which alters RNA, DNA, and protein synthesis. The mechanism of action of glutaraldehydes are reviewed extensively elsewhere 592, 593 .

Microbicidal Activity.

The in vitro inactivation of microorganisms by glutaraldehydes has been extensively investigated and reviewed 592, 593 . Several investigators showed that &ge2% aqueous solutions of glutaraldehyde, buffered to pH 7.5&ndash8.5 with sodium bicarbonate effectively killed vegetative bacteria in <2 minutes M. tuberculosis, fungi, and viruses in <10 minutes and spores of Bacillus and Clostridium species in 3 hours 542, 592-597 . Spores of C. difficile are more rapidly killed by 2% glutaraldehyde than are spores of other species of Clostridium and Bacillus 79, 265, 266 . Microorganisms with substantial resistance to glutaraldehyde have been reported, including some mycobacteria (M. chelonae, Mycobacterium avium-intracellulare, M. xenopi) 598-601 , Methylobacterium mesophilicum 602 , Trichosporon, fungal ascospores (e.g., Microascus cinereus, Cheatomium globosum), and Cryptosporidium 271, 603 . M. chelonae persisted in a 0.2% glutaraldehyde solution used to store porcine prosthetic heart valves 604 .

Two percent alkaline glutaraldehyde solution inactivated 10 5 M. tuberculosis cells on the surface of penicylinders within 5 minutes at 18°C 589 . However, subsequent studies 82 questioned the mycobactericidal prowess of glutaraldehydes. Two percent alkaline glutaraldehyde has slow action (20 to >30 minutes) against M. tuberculosis and compares unfavorably with alcohols, formaldehydes, iodine, and phenol 82 . Suspensions of M. avium, M. intracellulare, and M. gordonae were more resistant to inactivation by a 2% alkaline glutaraldehyde (estimated time to complete inactivation:

60 minutes) than were virulent M. tuberculosis (estimated time to complete inactivation

25 minutes) 605 . The rate of kill was directly proportional to the temperature, and a standardized suspension of M. tuberculosis could not be sterilized within 10 minutes 84 . An FDA-cleared chemical sterilant containing 2.5% glutaraldehyde uses increased temperature (35°C) to reduce the time required to achieve high-level disinfection (5 minutes) 85, 606 , but its use is limited to automatic endoscope reprocessors equipped with a heater. In another study employing membrane filters for measurement of mycobactericidal activity of 2% alkaline glutaraldehyde, complete inactivation was achieved within 20 minutes at 20°C when the test inoculum was 10 6 M. tuberculosis per membrane 81 . Several investigators 55, 57, 73, 76, 80, 81, 84, 605 have demonstrated that glutaraldehyde solutions inactivate 2.4 to >5.0 log10 of M. tuberculosis in 10 minutes (including multidrug-resistant M. tuberculosis) and 4.0&ndash6.4 log10 of M. tuberculosis in 20 minutes. On the basis of these data and other studies, 20 minutes at room temperature is considered the minimum exposure time needed to reliably kill Mycobacteria and other vegetative bacteria with &ge2% glutaraldehyde 17, 19, 27, 57, 83, 94, 108, 111, 117-121, 607 .

Glutaraldehyde is commonly diluted during use, and studies showed a glutaraldehyde concentration decline after a few days of use in an automatic endoscope washer 608, 609 . The decline occurs because instruments are not thoroughly dried and water is carried in with the instrument, which increases the solution&rsquos volume and dilutes its effective concentration 610 . This emphasizes the need to ensure that semicritical equipment is disinfected with an acceptable concentration of glutaraldehyde. Data suggest that 1.0%&ndash1.5% glutaraldehyde is the minimum effective concentration for >2% glutaraldehyde solutions when used as a high-level disinfectant 76, 589, 590, 609 . Chemical test strips or liquid chemical monitors 610, 611 are available for determining whether an effective concentration of glutaraldehyde is present despite repeated use and dilution. The frequency of testing should be based on how frequently the solutions are used (e.g., used daily, test daily used weekly, test before use used 30 times per day, test each 10th use), but the strips should not be used to extend the use life beyond the expiration date. Data suggest the chemicals in the test strip deteriorate with time 612 and a manufacturer&rsquos expiration date should be placed on the bottles. The bottle of test strips should be dated when opened and used for the period of time indicated on the bottle (e.g., 120 days). The results of test strip monitoring should be documented. The glutaraldehyde test kits have been preliminarily evaluated for accuracy and range 612 but the reliability has been questioned 613 . To ensure the presence of minimum effective concentration of the high-level disinfectant, manufacturers of some chemical test strips recommend the use of quality-control procedures to ensure the strips perform properly. If the manufacturer of the chemical test strip recommends a quality-control procedure, users should comply with the manufacturer&rsquos recommendations. The concentration should be considered unacceptable or unsafe when the test indicates a dilution below the product&rsquos minimum effective concentration (MEC) (generally to &le1.0%&ndash1.5% glutaraldehyde) by the indicator not changing color.

A 2.0% glutaraldehyde&ndash7.05% phenol&ndash1.20% sodium phenate product that contained 0.125% glutaraldehyde&ndash0.44% phenol&ndash0.075% sodium phenate when diluted 1:16 is not recommended as a high-level disinfectant because it lacks bactericidal activity in the presence of organic matter and lacks tuberculocidal, fungicidal, virucidal, and sporicidal activity 49, 55, 56, 71, 73-79, 614 . In December 1991, EPA issued an order to stop the sale of all batches of this product because of efficacy data showing the product is not effective against spores and possibly other microorganisms or inanimate objects as claimed on the label 615 . FDA has cleared a glutaraldehyde&ndashphenol/phenate concentrate as a high-level disinfectant that contains 1.12% glutaraldehyde with 1.93% phenol/phenate at its use concentration. Other FDA cleared glutaraldehyde sterilants that contain 2.4%&ndash3.4% glutaraldehyde are used undiluted 606 .

Glutaraldehyde is used most commonly as a high-level disinfectant for medical equipment such as endoscopes 69, 107, 504 , spirometry tubing, dialyzers 616 , transducers, anesthesia and respiratory therapy equipment 617 , hemodialysis proportioning and dialysate delivery systems 249, 618 , and reuse of laparoscopic disposable plastic trocars 619 . Glutaraldehyde is noncorrosive to metal and does not damage lensed instruments, rubber. or plastics. Glutaraldehyde should not be used for cleaning noncritical surfaces because it is too toxic and expensive.

Colitis believed caused by glutaraldehyde exposure from residual disinfecting solution in endoscope solution channels has been reported and is preventable by careful endoscope rinsing 318, 620-630 . One study found that residual glutaraldehyde levels were higher and more variable after manual disinfection (<0.2 mg/L to 159.5 mg/L) than after automatic disinfection (0.2&ndash6.3 mg/L) 631 . Similarly, keratopathy and corneal decompensation were caused by ophthalmic instruments that were inadequately rinsed after soaking in 2% glutaraldehyde 632, 633 .

Healthcare personnel can be exposed to elevated levels of glutaraldehyde vapor when equipment is processed in poorly ventilated rooms, when spills occur, when glutaraldehyde solutions are activated or changed, 634 , or when open immersion baths are used. Acute or chronic exposure can result in skin irritation or dermatitis, mucous membrane irritation (eye, nose, mouth), or pulmonary symptoms 318, 635-639 . Epistaxis, allergic contact dermatitis, asthma, and rhinitis also have been reported in healthcare workers exposed to glutaraldehyde 636, 640-647 .

Glutaraldehyde exposure should be monitored to ensure a safe work environment. Testing can be done by four techniques: a silica gel tube/gas chromatography with a flame ionization detector, dinitrophenylhydrazine (DNPH)-impregnated filter cassette/high-performance liquid chromatography (HPLC) with an ultraviolet (UV) detector, a passive badge/HPLC, or a handheld glutaraldehyde air monitor 648 . The silica gel tube and the DNPH-impregnated cassette are suitable for monitoring the 0.05 ppm ceiling limit. The passive badge, with a 0.02 ppm limit of detection, is considered marginal at the Americal Council of Governmental Industrial Hygienists (ACGIH) ceiling level. The ceiling level is considered too close to the glutaraldehyde meter&rsquos 0.03 ppm limit of detection to provide confidence in the readings 648 . ACGIH does not require a specific monitoring schedule for glutaraldehyde however, a monitoring schedule is needed to ensure the level is less than the ceiling limit. For example, monitoring should be done initially to determine glutaraldehyde levels, after procedural or equipment changes, and in response to worker complaints 649 . In the absence of an OSHA permissible exposure limit, if the glutaraldehyde level is higher than the ACGIH ceiling limit of 0.05 ppm, corrective action and repeat monitoring would be prudent 649 .

Engineering and work-practice controls that can be used to resolve these problems include ducted exhaust hoods, air systems that provide 7&ndash15 air exchanges per hour, ductless fume hoods with absorbents for the glutaraldehyde vapor, tight-fitting lids on immersion baths, personal protection (e.g., nitrile or butyl rubber gloves but not natural latex gloves, goggles) to minimize skin or mucous membrane contact, and automated endoscope processors 7, 650 . If engineering controls fail to maintain levels below the ceiling limit, institutions can consider the use of respirators (e.g., a half-face respirator with organic vapor cartridge 640 or a type &ldquoC&rdquo supplied air respirator with a full facepiece operated in a positive pressure mode) 651 . In general, engineering controls are preferred over work-practice and administrative controls because they do not require active participation by the health-care worker. Even though enforcement of the OSHA ceiling limit was suspended in 1993 by the U.S. Court of Appeals 577 , limiting employee exposure to 0.05 ppm (according to ACGIH) is prudent because, at this level, glutaraldehyde can irritate the eyes, throat, and nose 318, 577, 639, 652 . If glutaraldehyde disposal through the sanitary sewer system is restricted, sodium bisulfate can be used to neutralize the glutaraldehyde and make it safe for disposal.

Hydrogen Peroxide

Overview.

The literature contains several accounts of the properties, germicidal effectiveness, and potential uses for stabilized hydrogen peroxide in the health-care setting. Published reports ascribe good germicidal activity to hydrogen peroxide and attest to its bactericidal, virucidal, sporicidal, and fungicidal properties 653-655 . (Tables 4 and 5) The FDA website lists cleared liquid chemical sterilants and high-level disinfectants containing hydrogen peroxide and their cleared contact conditions.

Mode of Action.

Hydrogen peroxide works by producing destructive hydroxyl free radicals that can attack membrane lipids, DNA, and other essential cell components. Catalase, produced by aerobic organisms and facultative anaerobes that possess cytochrome systems, can protect cells from metabolically produced hydrogen peroxide by degrading hydrogen peroxide to water and oxygen. This defense is overwhelmed by the concentrations used for disinfection 653, 654 .

Microbicidal Activity.

Hydrogen peroxide is active against a wide range of microorganisms, including bacteria, yeasts, fungi, viruses, and spores 78, 654 . A 0.5% accelerated hydrogen peroxide demonstrated bactericidal and virucidal activity in 1 minute and mycobactericidal and fungicidal activity in 5 minutes 656 . Bactericidal effectiveness and stability of hydrogen peroxide in urine has been demonstrated against a variety of health-care&ndashassociated pathogens organisms with high cellular catalase activity (e.g., S. aureus, S. marcescens, and Proteus mirabilis) required 30&ndash60 minutes of exposure to 0.6% hydrogen peroxide for a 10 8 reduction in cell counts, whereas organisms with lower catalase activity (e.g., E. coli, Streptococcus species, and Pseudomonas species) required only 15 minutes&rsquo exposure 657 . In an investigation of 3%, 10%, and 15% hydrogen peroxide for reducing spacecraft bacterial populations, a complete kill of 10 6 spores (i.e., Bacillus species) occurred with a 10% concentration and a 60-minute exposure time. A 3% concentration for 150 minutes killed 10 6 spores in six of seven exposure trials 658 . A 10% hydrogen peroxide solution resulted in a 10 3 decrease in B. atrophaeus spores, and a &ge10 5 decrease when tested against 13 other pathogens in 30 minutes at 20°C 659, 660 . A 3.0% hydrogen peroxide solution was ineffective against VRE after 3 and 10 minutes exposure times 661 and caused only a 2-log10 reduction in the number of Acanthamoeba cysts in approximately 2 hours 662 . A 7% stabilized hydrogen peroxide proved to be sporicidal (6 hours of exposure), mycobactericidal (20 minutes), fungicidal (5 minutes) at full strength, virucidal (5 minutes) and bactericidal (3 minutes) at a 1:16 dilution when a quantitative carrier test was used 655 . The 7% solution of hydrogen peroxide, tested after 14 days of stress (in the form of germ-loaded carriers and respiratory therapy equipment), was sporicidal (>7 log10 reduction in 6 hours), mycobactericidal (>6.5 log10 reduction in 25 minutes), fungicidal (>5 log10 reduction in 20 minutes), bactericidal (>6 log10 reduction in 5 minutes) and virucidal (5 log10 reduction in 5 minutes) 663 . Synergistic sporicidal effects were observed when spores were exposed to a combination of hydrogen peroxide (5.9%&ndash23.6%) and peracetic acid 664 . Other studies demonstrated the antiviral activity of hydrogen peroxide against rhinovirus 665 . The time required for inactivating three serotypes of rhinovirus using a 3% hydrogen peroxide solution was 6&ndash8 minutes this time increased with decreasing concentrations (18-20 minutes at 1.5%, 50&ndash60 minutes at 0.75%).

Concentrations of hydrogen peroxide from 6% to 25% show promise as chemical sterilants. The product marketed as a sterilant is a premixed, ready-to-use chemical that contains 7.5% hydrogen peroxide and 0.85% phosphoric acid (to maintain a low pH) 69 . The mycobactericidal activity of 7.5% hydrogen peroxide has been corroborated in a study showing the inactivation of >10 5 multidrug-resistant M. tuberculosis after a 10-minute exposure 666 . Thirty minutes were required for >99.9% inactivation of poliovirus and HAV 667 . Three percent and 6% hydrogen peroxide were unable to inactivate HAV in 1 minute in a carrier test 58 . When the effectiveness of 7.5% hydrogen peroxide at 10 minutes was compared with 2% alkaline glutaraldehyde at 20 minutes in manual disinfection of endoscopes, no significant difference in germicidal activity was observed 668 . ). No complaints were received from the nursing or medical staff regarding odor or toxicity. In one study, 6% hydrogen peroxide (unused product was 7.5%) was more effective in the high-level disinfection of flexible endoscopes than was the 2% glutaraldehyde solution 456 . A new, rapid-acting 13.4% hydrogen peroxide formulation (that is not yet FDA-cleared) has demonstrated sporicidal, mycobactericidal, fungicidal, and virucidal efficacy. Manufacturer data demonstrate that this solution sterilizes in 30 minutes and provides high-level disinfection in 5 minutes 669 . This product has not been used long enough to evaluate material compatibility to endoscopes and other semicritical devices, and further assessment by instrument manufacturers is needed.

Under normal conditions, hydrogen peroxide is extremely stable when properly stored (e.g., in dark containers). The decomposition or loss of potency in small containers is less than 2% per year at ambient temperatures 670 .

Commercially available 3% hydrogen peroxide is a stable and effective disinfectant when used on inanimate surfaces. It has been used in concentrations from 3% to 6% for disinfecting soft contact lenses (e.g., 3% for 2&ndash3 hrs) 653, 671, 672 , tonometer biprisms 513 , ventilators 673 , fabrics 397 , and endoscopes 456 . Hydrogen peroxide was effective in spot-disinfecting fabrics in patients&rsquo rooms 397 . Corneal damage from a hydrogen peroxide-soaked tonometer tip that was not properly rinsed has been reported 674 . Hydrogen peroxide also has been instilled into urinary drainage bags in an attempt to eliminate the bag as a source of bladder bacteriuria and environmental contamination 675 . Although the instillation of hydrogen peroxide into the bag reduced microbial contamination of the bag, this procedure did not reduce the incidence of catheter-associated bacteriuria 675 .

A chemical irritation resembling pseudomembranous colitis caused by either 3% hydrogen peroxide or a 2% glutaraldehyde has been reported 621 . An epidemic of pseudomembrane-like enteritis and colitis in seven patients in a gastrointestinal endoscopy unit also has been associated with inadequate rinsing of 3% hydrogen peroxide from the endoscope 676 .

As with other chemical sterilants, dilution of the hydrogen peroxide must be monitored by regularly testing the minimum effective concentration (i.e., 7.5%&ndash6.0%). Compatibility testing by Olympus America of the 7.5% hydrogen peroxide found both cosmetic changes (e.g., discoloration of black anodized metal finishes) 69 and functional changes with the tested endoscopes (Olympus, written communication, October 15, 1999).

Iodophors

Overview.

Iodine solutions or tinctures long have been used by health professionals primarily as antiseptics on skin or tissue. Iodophors, on the other hand, have been used both as antiseptics and disinfectants. FDA has not cleared any liquid chemical sterilant or high-level disinfectants with iodophors as the main active ingredient. An iodophor is a combination of iodine and a solubilizing agent or carrier the resulting complex provides a sustained-release reservoir of iodine and releases small amounts of free iodine in aqueous solution. The best-known and most widely used iodophor is povidone-iodine, a compound of polyvinylpyrrolidone with iodine. This product and other iodophors retain the germicidal efficacy of iodine but unlike iodine generally are nonstaining and relatively free of toxicity and irritancy 677, 678 .

Several reports that documented intrinsic microbial contamination of antiseptic formulations of povidone-iodine and poloxamer-iodine 679-681 caused a reappraisal of the chemistry and use of iodophors 682 . &ldquoFree&rdquo iodine (I2) contributes to the bactericidal activity of iodophors and dilutions of iodophors demonstrate more rapid bactericidal action than does a full-strength povidone-iodine solution. The reason for the observation that dilution increases bactericidal activity is unclear, but dilution of povidone-iodine might weaken the iodine linkage to the carrier polymer with an accompanying increase of free iodine in solution 680 . Therefore, iodophors must be diluted according to the manufacturers&rsquo directions to achieve antimicrobial activity.

Mode of Action.

Iodine can penetrate the cell wall of microorganisms quickly, and the lethal effects are believed to result from disruption of protein and nucleic acid structure and synthesis.

Microbicidal Activity.

Published reports on the in vitro antimicrobial efficacy of iodophors demonstrate that iodophors are bactericidal, mycobactericidal, and virucidal but can require prolonged contact times to kill certain fungi and bacterial spores 14, 71-73, 290, 683-686 . Three brands of povidone-iodine solution have demonstrated more rapid kill (seconds to minutes) of S. aureus and M. chelonae at a 1:100 dilution than did the stock solution 683 . The virucidal activity of 75&ndash150 ppm available iodine was demonstrated against seven viruses 72 . Other investigators have questioned the efficacy of iodophors against poliovirus in the presence of organic matter 685 and rotavirus SA-11 in distilled or tapwater 290 . Manufacturers&rsquo data demonstrate that commercial iodophors are not sporicidal, but they are tuberculocidal, fungicidal, virucidal, and bactericidal at their recommended use-dilution.

Besides their use as an antiseptic, iodophors have been used for disinfecting blood culture bottles and medical equipment, such as hydrotherapy tanks, thermometers, and endoscopes. Antiseptic iodophors are not suitable for use as hard-surface disinfectants because of concentration differences. Iodophors formulated as antiseptics contain less free iodine than do those formulated as disinfectants 376 . Iodine or iodine-based antiseptics should not be used on silicone catheters because they can adversely affect the silicone tubing 687 .

Ortho-phthalaldehyde (OPA)

Overview.

Ortho-phthalaldehyde is a high-level disinfectant that received FDA clearance in October 1999. It contains 0.55% 1,2-benzenedicarboxaldehyde (OPA). OPA solution is a clear, pale-blue liquid with a pH of 7.5. (Tables 4 and 5)

Mode of Action.

Preliminary studies on the mode of action of OPA suggest that both OPA and glutaraldehyde interact with amino acids, proteins, and microorganisms. However, OPA is a less potent cross-linking agent. This is compensated for by the lipophilic aromatic nature of OPA that is likely to assist its uptake through the outer layers of mycobacteria and gram-negative bacteria 688-690 . OPA appears to kill spores by blocking the spore germination process 691 .

Microbicidal Activity.

Studies have demonstrated excellent microbicidal activity in vitro 69, 100, 271, 400, 692-703 . For example, OPA has superior mycobactericidal activity (5-log10 reduction in 5 minutes) to glutaraldehyde. The mean times required to produce a 6-log10 reduction for M. bovis using 0.21% OPA was 6 minutes, compared with 32 minutes using 1.5% glutaraldehyde 693 . OPA showed good activity against the mycobacteria tested, including the glutaraldehyde-resistant strains, but 0.5% OPA was not sporicidal with 270 minutes of exposure. Increasing the pH from its unadjusted level (about 6.5) to pH 8 improved the sporicidal activity of OPA 694 . The level of biocidal activity was directly related to the temperature. A greater than 5-log10 reduction of B. atrophaeus spores was observed in 3 hours at 35°C, than in 24 hours at 20°C. Also, with an exposure time &le5 minutes, biocidal activity decreased with increasing serum concentration. However, efficacy did not differ when the exposure time was &ge10 minutes 697 . In addition, OPA is effective (>5-log10 reduction) against a wide range of microorganisms, including glutaraldehyde-resistant mycobacteria and B. atrophaeus spores 694 .

The influence of laboratory adaptation of test strains, such as P. aeruginosa, to 0.55% OPA has been evaluated. Resistant and multiresistant strains increased substantially in susceptibility to OPA after laboratory adaptation (log10 reduction factors increased by 0.54 and 0.91 for resistant and multiresistant strains, respectively) 704 . Other studies have found naturally occurring cells of P. aeurginosa were more resistant to a variety of disinfectants than were subcultured cells 705 .

OPA has several potential advantages over glutaraldehyde. It has excellent stability over a wide pH range (pH 3&ndash9), is not a known irritant to the eyes and nasal passages 706 , does not require exposure monitoring, has a barely perceptible odor, and requires no activation. OPA, like glutaraldehyde, has excellent material compatibility. A potential disadvantage of OPA is that it stains proteins gray (including unprotected skin) and thus must be handled with caution 69 . However, skin staining would indicate improper handling that requires additional training and/or personal protective equipment (e.g., gloves, eye and mouth protection, and fluid-resistant gowns). OPA residues remaining on inadequately water-rinsed transesophageal echo probes can stain the patient&rsquos mouth 707 . Meticulous cleaning, using the correct OPA exposure time (e.g., 12 minutes) and copious rinsing of the probe with water should eliminate this problem. The results of one study provided a basis for a recommendation that rinsing of instruments disinfected with OPA will require at least 250 mL of water per channel to reduce the chemical residue to a level that will not compromise patient or staff safety (<1 ppm) 708 . Personal protective equipment should be worn when contaminated instruments, equipment, and chemicals are handled 400 . In addition, equipment must be thoroughly rinsed to prevent discoloration of a patient&rsquos skin or mucous membrane.

In April 2004, the manufacturer of OPA disseminated information to users about patients who reportedly experienced an anaphylaxis-like reaction after cystoscopy where the scope had been reprocessed using OPA. Of approximately 1 million urologic procedures performed using instruments reprocessed using OPA, 24 cases (17 cases in the United States, six in Japan, one in the United Kingdom) of anaphylaxis-like reactions have been reported after repeated cystoscopy (typically after four to nine treatments). Preventive measures include removal of OPA residues by thorough rinsing and not using OPA for reprocessing urologic instrumentation used to treat patients with a history of bladder cancer (Nevine Erian, personal communication, June 4, 2004 Product Notification, Advanced Sterilization Products, April 23, 2004) 709 .

A few OPA clinical studies are available. In a clinical-use study, OPA exposure of 100 endoscopes for 5 minutes resulted in a >5-log10 reduction in bacterial load. Furthermore, OPA was effective over a 14-day use cycle 100 . Manufacturer data show that OPA will last longer in an automatic endoscope reprocessor before reaching its MEC limit (MEC after 82 cycles) than will glutaraldehyde (MEC after 40 cycles) 400 . High-pressure liquid chromatography confirmed that OPA levels are maintained above 0.3% for at least 50 cycles 706, 710 . OPA must be disposed in accordance with local and state regulations. If OPA disposal through the sanitary sewer system is restricted, glycine (25 grams/gallon) can be used to neutralize the OPA and make it safe for disposal.

The high-level disinfectant label claims for OPA solution at 20°C vary worldwide (e.g., 5 minutes in Europe, Asia, and Latin America 10 minutes in Canada and Australia and 12 minutes in the United States). These label claims differ worldwide because of differences in the test methodology and requirements for licensure. In an automated endoscope reprocessor with an FDA-cleared capability to maintain solution temperatures at 25°C, the contact time for OPA is 5 minutes.

Peracetic Acid

Overview.

Peracetic, or peroxyacetic, acid is characterized by rapid action against all microorganisms. Special advantages of peracetic acid are that it lacks harmful decomposition products (i.e., acetic acid, water, oxygen, hydrogen peroxide), enhances removal of organic material 711 , and leaves no residue. It remains effective in the presence of organic matter and is sporicidal even at low temperatures (Tables 4 and 5). Peracetic acid can corrode copper, brass, bronze, plain steel, and galvanized iron but these effects can be reduced by additives and pH modifications. It is considered unstable, particularly when diluted for example, a 1% solution loses half its strength through hydrolysis in 6 days, whereas 40% peracetic acid loses 1%&ndash2% of its active ingredients per month 654 .

Mode of Action.

Little is known about the mechanism of action of peracetic acid, but it is believed to function similarly to other oxidizing agents&mdashthat is, it denatures proteins, disrupts the cell wall permeability, and oxidizes sulfhydryl and sulfur bonds in proteins, enzymes, and other metabolites 654 .

Microbicidal Activity.

Peracetic acid will inactivate gram-positive and gram-negative bacteria, fungi, and yeasts in &le5 minutes at <100 ppm. In the presence of organic matter, 200&ndash500 ppm is required. For viruses, the dosage range is wide (12&ndash2250 ppm), with poliovirus inactivated in yeast extract in 15 minutes with 1,500&ndash2,250 ppm. In one study, 3.5% peracetic acid was ineffective against HAV after 1-minute exposure using a carrier test 58 . Peracetic acid (0.26%) was effective (log10 reduction factor >5) against all test strains of mycobacteria (M. tuberculosis, M. avium-intracellulare, M. chelonae, and M. fortuitum) within 20&ndash30 minutes in the presence or absence of an organic load 607, 712 . With bacterial spores, 500&ndash10,000 ppm (0.05%&ndash1%) inactivates spores in 15 seconds to 30 minutes using a spore suspension test 654, 659, 713-715 .

An automated machine using peracetic acid to chemically sterilize medical (e.g., endoscopes, arthroscopes), surgical, and dental instruments is used in the United States 716-718 . As previously noted, dental handpieces should be steam sterilized. The sterilant, 35% peracetic acid, is diluted to 0.2% with filtered water at 50°C. Simulated-use trials have demonstrated excellent microbicidal activity 111, 718-722 , and three clinical trials have demonstrated both excellent microbial killing and no clinical failures leading to infection 90, 723, 724 . The high efficacy of the system was demonstrated in a comparison of the efficacies of the system with that of ethylene oxide. Only the peracetic acid system completely killed 6 log10 of M. chelonae, E. faecalis, and B. atrophaeus spores with both an organic and inorganic challenge 722 . An investigation that compared the costs, performance, and maintenance of urologic endoscopic equipment processed by high-level disinfection (with glutaraldehyde) with those of the peracetic acid system reported no clinical differences between the two systems. However, the use of this system led to higher costs than the high-level disinfection, including costs for processing ($6.11 vs. .45 per cycle), purchasing and training ($24,845 vs. $16), installation ($5,800 vs. ), and endoscope repairs ($6,037 vs. $445) 90 . Furthermore, three clusters of infection using the peracetic acid automated endoscope reprocessor were linked to inadequately processed bronchoscopes when inappropriate channel connectors were used with the system 725 . These clusters highlight the importance of training, proper model-specific endoscope connector systems, and quality-control procedures to ensure compliance with endoscope manufacturer recommendations and professional organization guidelines. An alternative high-level disinfectant available in the United Kingdom contains 0.35% peracetic acid. Although this product is rapidly effective against a broad range of microorganisms 466, 726, 727 , it tarnishes the metal of endoscopes and is unstable, resulting in only a 24-hour use life 727 .

Peracetic Acid and Hydrogen Peroxide

Overview.

Two chemical sterilants are available that contain peracetic acid plus hydrogen peroxide (i.e., 0.08% peracetic acid plus 1.0% hydrogen peroxide [no longer marketed] and 0.23% peracetic acid plus 7.35% hydrogen peroxide (Tables 4 and 5).

Microbicidal Activity.

The bactericidal properties of peracetic acid and hydrogen peroxide have been demonstrated 728 . Manufacturer data demonstrated this combination of peracetic acid and hydrogen peroxide inactivated all microorganisms except bacterial spores within 20 minutes. The 0.08% peracetic acid plus 1.0% hydrogen peroxide product effectively inactivated glutaraldehyde-resistant mycobacteria 729 .

The combination of peracetic acid and hydrogen peroxide has been used for disinfecting hemodialyzers 730 . The percentage of dialysis centers using a peracetic acid-hydrogen peroxide-based disinfectant for reprocessing dialyzers increased from 5% in 1983 to 56% in 1997 249 . Olympus America does not endorse use of 0.08% peracetic acid plus 1.0% hydrogen peroxide (Olympus America, personal communication, April 15, 1998) on any Olympus endoscope because of cosmetic and functional damage and will not assume liability for chemical damage resulting from use of this product. This product is not currently available. FDA has cleared a newer chemical sterilant with 0.23% peracetic acid and 7.35% hydrogen peroxide (Tables 4 and 5). After testing the 7.35% hydrogen peroxide and 0.23% peracetic acid product, Olympus America concluded it was not compatible with the company&rsquos flexible gastrointestinal endoscopes this conclusion was based on immersion studies where the test insertion tubes had failed because of swelling and loosening of the black polymer layer of the tube (Olympus America, personal communication, September 13, 2000).

Phenolics

Overview.

Phenol has occupied a prominent place in the field of hospital disinfection since its initial use as a germicide by Lister in his pioneering work on antiseptic surgery. In the past 30 years, however, work has concentrated on the numerous phenol derivatives or phenolics and their antimicrobial properties. Phenol derivatives originate when a functional group (e.g., alkyl, phenyl, benzyl, halogen) replaces one of the hydrogen atoms on the aromatic ring. Two phenol derivatives commonly found as constituents of hospital disinfectants are ortho-phenylphenol and ortho-benzyl-para-chlorophenol. The antimicrobial properties of these compounds and many other phenol derivatives are much improved over those of the parent chemical. Phenolics are absorbed by porous materials, and the residual disinfectant can irritate tissue. In 1970, depigmentation of the skin was reported to be caused by phenolic germicidal detergents containing para-tertiary butylphenol and para-tertiary amylphenol 731 .

Mode of Action.

In high concentrations, phenol acts as a gross protoplasmic poison, penetrating and disrupting the cell wall and precipitating the cell proteins. Low concentrations of phenol and higher molecular-weight phenol derivatives cause bacterial death by inactivation of essential enzyme systems and leakage of essential metabolites from the cell wall 732 .

Microbicidal Activity.

Published reports on the antimicrobial efficacy of commonly used phenolics showed they were bactericidal, fungicidal, virucidal, and tuberculocidal 14, 61, 71, 73, 227, 416, 573, 732-738 . One study demonstrated little or no virucidal effect of a phenolic against coxsackie B4, echovirus 11, and poliovirus 1 736 . Similarly, 12% ortho-phenylphenol failed to inactivate any of the three hydrophilic viruses after a 10-minute exposure time, although 5% phenol was lethal for these viruses 72 . A 0.5% dilution of a phenolic (2.8% ortho-phenylphenol and 2.7% ortho-benzyl-para-chlorophenol) inactivated HIV 227 and a 2% solution of a phenolic (15% ortho-phenylphenol and 6.3% para-tertiary-amylphenol) inactivated all but one of 11 fungi tested 71 .

Manufacturers&rsquo data using the standardized AOAC methods demonstrate that commercial phenolics are not sporicidal but are tuberculocidal, fungicidal, virucidal, and bactericidal at their recommended use-dilution. Attempts to substantiate the bactericidal label claims of phenolics using the AOAC Use-Dilution Method occasionally have failed 416, 737 . However, results from these same studies have varied dramatically among laboratories testing identical products.

Many phenolic germicides are EPA-registered as disinfectants for use on environmental surfaces (e.g., bedside tables, bedrails, and laboratory surfaces) and noncritical medical devices. Phenolics are not FDA-cleared as high-level disinfectants for use with semicritical items but could be used to preclean or decontaminate critical and semicritical devices before terminal sterilization or high-level disinfection.

The use of phenolics in nurseries has been questioned because of hyperbilirubinemia in infants placed in bassinets where phenolic detergents were used 739 . In addition, bilirubin levels were reported to increase in phenolic-exposed infants, compared with nonphenolic-exposed infants, when the phenolic was prepared according to the manufacturers&rsquo recommended dilution 740 . If phenolics are used to clean nursery floors, they must be diluted as recommended on the product label. Phenolics (and other disinfectants) should not be used to clean infant bassinets and incubators while occupied. If phenolics are used to terminally clean infant bassinets and incubators, the surfaces should be rinsed thoroughly with water and dried before reuse of infant bassinets and incubators 17 .

Quaternary Ammonium Compounds

Overview.

The quaternary ammonium compounds are widely used as disinfectants. Health-care&ndashassociated infections have been reported from contaminated quaternary ammonium compounds used to disinfect patient-care supplies or equipment, such as cystoscopes or cardiac catheters 741, 742 . The quaternaries are good cleaning agents, but high water hardness 743 and materials such as cotton and gauze pads can make them less microbicidal because of insoluble precipitates or cotton and gauze pads absorb the active ingredients, respectively. One study showed a significant decline (

40%&ndash50% lower at 1 hour) in the concentration of quaternaries released when cotton rags or cellulose-based wipers were used in the open-bucket system, compared with the nonwoven spunlace wipers in the closed-bucket system. 744 As with several other disinfectants (e.g., phenolics, iodophors) gram-negative bacteria can survive or grow in them 404 .

Chemically, the quaternaries are organically substituted ammonium compounds in which the nitrogen atom has a valence of 5, four of the substituent radicals (R1-R4) are alkyl or heterocyclic radicals of a given size or chain length, and the fifth (X ‑ ) is a halide, sulfate, or similar radical 745 . Each compound exhibits its own antimicrobial characteristics, hence the search for one compound with outstanding antimicrobial properties. Some of the chemical names of quaternary ammonium compounds used in healthcare are alkyl dimethyl benzyl ammonium chloride, alkyl didecyl dimethyl ammonium chloride, and dialkyl dimethyl ammonium chloride. The newer quaternary ammonium compounds (i.e., fourth generation), referred to as twin-chain or dialkyl quaternaries (e.g. didecyl dimethyl ammonium bromide and dioctyl dimethyl ammonium bromide), purportedly remain active in hard water and are tolerant of anionic residues 746 .

A few case reports have documented occupational asthma as a result of exposure to benzalkonium chloride 747 .

Mode of Action.

The bactericidal action of the quaternaries has been attributed to the inactivation of energy-producing enzymes, denaturation of essential cell proteins, and disruption of the cell membrane 746 . Evidence exists that supports these and other possibilities 745 748 .

Microbicidal Activity.

Results from manufacturers&rsquo data sheets and from published scientific literature indicate that the quaternaries sold as hospital disinfectants are generally fungicidal, bactericidal, and virucidal against lipophilic (enveloped) viruses they are not sporicidal and generally not tuberculocidal or virucidal against hydrophilic (nonenveloped) viruses 14, 54-56, 58, 59, 61, 71, 73, 186, 297, 748, 749 . The poor mycobactericidal activities of quaternary ammonium compounds have been demonstrated 55, 73 . Quaternary ammonium compounds (as well as 70% isopropyl alcohol, phenolic, and a chlorine-containing wipe [80 ppm]) effectively (>95%) remove and/or inactivate contaminants (i.e., multidrug-resistant S. aureus, vancomycin-resistant Entercoccus, P. aeruginosa) from computer keyboards with a 5-second application time. No functional damage or cosmetic changes occurred to the computer keyboards after 300 applications of the disinfectants 45 .

Attempts to reproduce the manufacturers&rsquo bactericidal and tuberculocidal claims using the AOAC tests with a limited number of quaternary ammonium compounds occasionally have failed 73, 416, 737 . However, test results have varied extensively among laboratories testing identical products 416, 737 .


What are Enveloped Viruses?

Some viruses have an extra lipid membrane called envelope surrounding the protein capsid. These viruses belong to the virus group named ‘enveloped viruses’. The envelope contains phospholipids and proteins derived from host cell membranes. Enveloped viruses acquire this envelope during viral replication and release. HIV, HSV, HBV, and influenza virus are several examples of enveloped viruses. Moreover, some enveloped viruses contain spikes (made from glycoprotein) protruding from the envelope.

Figure 01: Enveloped Virus – HIV

Viral proteins in the envelope help the virus to bind with the host cell receptors. Viral envelope plays a major role in viral infections, including host recognition and entry. It helps the virus for attachment, transfer of genetic material to host cell and between cells, etc. Moreover, some viral envelopes help in determining characteristics of viral stability, such as resistance to chemical and physical inactivation. Enveloped viruses are more sensitive to biocides. Furthermore, they are sensitive to heat, dryness and acids.


Current Recommendations

The virion envelope is a fatty bilayer that surrounds the nucleic acid (i.e., genetic material) of the virus. Like any soap that mixes well with grease, the virion envelope dissolves when exposed to soap. And 20 seconds is sufficient to complete this process, at least for SARS-CoV-2. The exposed nucleic acids and proteins eventually degrade and can be washed away by water.

Alcohol also works the same way by tearing apart the virion envelope. The Centres for Disease Control and Prevention (CDC) says that hand sanitizers should be at least 60% alcohol to inhibit SARS-CoV-2. Though soap is still recommended as sweaty or dirty hands dilutes the sanitizer, lowering its efficacy.

“Soap, bleach, alcohol-based hand sanitizers, those alcohol sprays, these are really disruptive to the virus,” says the immunologist Professor Stuart Tangye at the Garvin Institute of Medical Research. “It doesn’t really stand a chance in the face of these sorts of cleansers which is great for us, some viruses are very hard to get rid of, but this one is pretty flimsy in that context.”


Bar or Liquid Soap: Which is More Effective to Kill COVID-19 Virus?

(Photo : Photo by Maddie Meyer/Getty Images) SOMERVILLE, MASSACHUSETTS - MARCH 21: A patron washes their hands at the hand washing station at the entrance of the Safe Supply outdoor grocery store at Bow Market on March 21, 2020 in Somerville, Massachusetts. In order to comply with the city of Somerville's food safety protocol and social distancing recommendations, patrons registered to shop in advance, stood six feet apart at all times, and vendors handled and bagged all food. COVID-19 has brought instability to the food service industry, forcing local farms and businesses to find new ways to sell directly to their community.

Wearing of masks has divided the country, but hand-washing is something that everyone would probably have the same opinion on. After all, hand-washing is one of the most crucial acts that could halt the spread of the new coronavirus.

But several millennials claimed that bar soaps are contaminated with germs, rather, they promote using liquid soap.

So what type of soap is actually recommended for hand-washing? Does the type of soap used for hand-washing really matter? Inverse looked into the issue in order to finally answer these queries.

On a statement made by a student doctor at the University of Oregon's Institute of Molecular Biology, it said that the size of disease-causing microbes is too small to be seen by a naked eye. But if these microbes could actually be seen, then we'll be able to determine if the coronavirus is on our hands and know when to hand-wash or avoid people.

With our normal sight, we are not capable of seeing trillions of microbes, which include fungi, bacteria, and viruses, that reside in our microbiomes, something that's being carried by all living creatures in their bodies. On the statement, the student doctor said how we are being described by one of their professors as walking clouds of microbes.

The different parts of our bodies, including the skin, cater specific micro-environment. Like the Peanut character in Pig-Pen, all of us are constantly acquiring and transferring microbes as we come across people and surfaces.

As carriers of different microbes and at the same time trying to protect ourselves from the new coronavirus, hand-washing for at least 20 seconds is advised by the experts. Since Covid-19 is transmitted by droplets from breathing, sneezing, and coughing, being cautious with our actions and proper hand-washing to prevent the virus from invading our body after we come to contact with other people and surfaces, can help impede the spread of the virus.

According to the World Health Organization proper hand-washing for at least 20 seconds reduces the number of microbes present on our hands. This is applicable whether you are using a bar or liquid soap. Both kinds have surfactants, which decrease surface tension that let soap to disperse. Soap surfactants are compounds that have dual properties one interacting with oil, dirt, and microbes present on the skin and the other interacting with water.

Covid-19 is an "enveloped" virus that is being adjoined by a lipid or fatty acid that is an easy mark for surfactants, which are essential in dissolving the membrane and killing the virus.

Bar and liquid soaps are fairly effective in lowering the number of microbes on our skin since both have surfactants. But aesthetically, they are different. Several people find the residues left of bar soaps on soap dishes as unpleasant to look at. To add on, bar and liquid soaps have a different carbon footprint.

Bar soaps have been used way back 2800BC. Vegetable or animal fats were transformed into soap and alcohol when it reacts with alkali. When rubbing your hands with bar soap, the friction created is bonus hygiene, as it might help remove debris better. Although some people worry that bar soaps may grow bacteria, it has been proven by studies that there is little to no chance of transmission from bar soap to hands when washing.

The mass production of liquid soaps, containing detergents that are artificially surfactants, started in the 1980s. Production of liquid soaps is more expensive. This requires five times the energy needed to produce bar soaps.

To battle Covid-19, using either type of soap does not matter. What matters now is we unite as a society and practice three lifesavers that we have, wearing masks, social distancing, and proper hand-washing.


Vaccines for Prevention

While we do have limited numbers of effective antiviral drugs, such as those used to treat HIV and influenza, the primary method of controlling viral disease is by vaccination, which is intended to prevent outbreaks by building immunity to a virus or virus family (Figure(PageIndex<1>)). Vaccines may be prepared using live viruses, killed viruses, or molecular subunits of the virus. The killed viral vaccines and subunit viruses are both incapable of causing disease.

Live viral vaccines are designed in the laboratory to cause few symptoms in recipients while giving them protective immunity against future infections. Polio was one disease that represented a milestone in the use of vaccines. Mass immunization campaigns in the 1950s (killed vaccine) and 1960s (live vaccine) significantly reduced the incidence of the disease, which caused muscle paralysis in children and generated a great amount of fear in the general population when regional epidemics occurred. The success of the polio vaccine paved the way for the routine dispensation of childhood vaccines against measles, mumps, rubella, chickenpox, and other diseases.

The danger of using live vaccines, which are usually more effective than killed vaccines, is the low but significant danger that these viruses will revert to their disease-causing form by back mutations . Live vaccines are usually made by attenuating (weakening) the &ldquowild-type&rdquo (disease-causing) virus by growing it in the laboratory in tissues or at temperatures different from what the virus is accustomed to in the host. Adaptations to these new cells or temperatures induce mutations in the genomes of the virus, allowing it to grow better in the laboratory while inhibiting its ability to cause disease when reintroduced into conditions found in the host. These attenuated viruses thus still cause infection, but they do not grow very well, allowing the immune response to develop in time to prevent major disease. Back mutations occur when the vaccine undergoes mutations in the host such that it readapts to the host and can again cause disease, which can then be spread to other humans in an epidemic. This type of scenario happened as recently as 2007 in Nigeria where mutations in a polio vaccine led to an epidemic of polio in that country.

Some vaccines are in continuous development because certain viruses, such as influenza and HIV, have a high mutation rate compared to other viruses and normal host cells. With influenza, mutations in the surface molecules of the virus help the organism evade the protective immunity that may have been obtained in a previous influenza season, making it necessary for individuals to get vaccinated every year. Other viruses, such as those that cause the childhood diseases measles, mumps, and rubella, mutate so infrequently that the same vaccine is used year after year.

Figure (PageIndex<2>): Vaccinations are designed to boost immunity to a virus to prevent infection. (credit: USACE Europe District)

Vaccines and Anti-viral Drugs for Treatment

In some cases, vaccines can be used to treat an active viral infection. The concept behind this is that by giving the vaccine, immunity is boosted without adding more disease-causing virus. In the case of rabies, a fatal neurological disease transmitted via the saliva of rabies virus-infected animals, the progression of the disease from the time of the animal bite to the time it enters the central nervous system may be 2 weeks or longer. This is enough time to vaccinate an individual who suspects that they have been bitten by a rabid animal, and their boosted immune response is sufficient to prevent the virus from entering nervous tissue. Thus, the potentially fatal neurological consequences of the disease are averted, and the individual only has to recover from the infected bite. This approach is also being used for the treatment of Ebola, one of the fastest and most deadly viruses on earth. Transmitted by bats and great apes, this disease can cause death in 70&ndash90 percent of infected humans within 2 weeks. Using newly developed vaccines that boost the immune response in this way, there is hope that affected individuals will be better able to control the virus, potentially saving a greater percentage of infected persons from a rapid and very painful death.

Another way of treating viral infections is the use of antiviral drugs. These drugs often have limited success in curing viral disease, but in many cases, they have been used to control and reduce symptoms for a wide variety of viral diseases. For most viruses, these drugs can inhibit the virus by blocking the actions of one or more of its proteins. It is important that the targeted proteins be encoded by viral genes and that these molecules are not present in a healthy host cell. In this way, viral growth is inhibited without damaging the host. There are large numbers of antiviral drugs available to treat infections, some specific for a particular virus and others that can affect multiple viruses.

Antivirals have been developed to treat genital herpes (herpes simplex II) and influenza. For genital herpes, drugs such as acyclovir can reduce the number and duration of episodes of active viral disease, during which patients develop viral lesions in their skin cells. As the virus remains latent in nervous tissue of the body for life, this drug is not curative but can make the symptoms of the disease more manageable. For influenza, drugs like Tamiflu (oseltamivir) (Figure (PageIndex<3>)) can reduce the duration of &ldquoflu&rdquo symptoms by 1 or 2 days, but the drug does not prevent symptoms entirely. Tamiflu works by inhibiting an enzyme (viral neuraminidase) that allows new virions to leave their infected cells. Thus, Tamiflu inhibits the spread of virus from infected to uninfected cells. Other antiviral drugs, such as Ribavirin, have been used to treat a variety of viral infections, although its mechanism of action against certain viruses remains unclear.

Figure (PageIndex<3>): (a) Tamiflu inhibits a viral enzyme called neuraminidase (NA) found in the influenza viral envelope. (b) Neuraminidase cleaves the connection between viral hemagglutinin (HA), also found in the viral envelope, and glycoproteins on the host cell surface. Inhibition of neuraminidase prevents the virus from detaching from the host cell, thereby blocking further infection. (credit a: modification of work by M. Eickmann)

By far, the most successful use of antivirals has been in the treatment of the retrovirus HIV, which causes a disease that, if untreated, is usually fatal within 10&ndash12 years after infection. Anti-HIV drugs have been able to control viral replication to the point that individuals receiving these drugs survive for a significantly longer time than the untreated.

Anti-HIV drugs inhibit viral replication at many different phases of the HIV replicative cycle (Figure (PageIndex<4>)). Drugs have been developed that inhibit the fusion of the HIV viral envelope with the plasma membrane of the host cell (fusion inhibitors), the conversion of its RNA genome into double-stranded DNA (reverse transcriptase inhibitors), the integration of the viral DNA into the host genome (integrase inhibitors), and the processing of viral proteins (protease inhibitors).

Figure (PageIndex<4>): HIV, an enveloped, icosahedral virus, attaches to the CD4 receptor of an immune cell and fuses with the cell membrane. Viral contents are released into the cell, where viral enzymes convert the single-stranded RNA genome into DNA and incorporate it into the host genome. (credit: NIAID, NIH)

When any of these drugs are used individually, the high mutation rate of the virus allows it to easily and rapidly develop resistance to the drug, limiting the drug&rsquos effectiveness. The breakthrough in the treatment of HIV was the development of HAART, highly active anti-retroviral therapy, which involves a mixture of different drugs, sometimes called a drug &ldquococktail.&rdquo By attacking the virus at different stages of its replicative cycle, it is much more difficult for the virus to develop resistance to multiple drugs at the same time. Still, even with the use of combination HAART therapy, there is concern that, over time, the virus will develop resistance to this therapy. Thus, new anti-HIV drugs are constantly being developed with the hope of continuing the battle against this highly fatal virus.

Everyday Connection: Applied Virology

The study of viruses has led to the development of a variety of new ways to treat non-viral diseases. Viruses have been used in gene therapy. Gene therapy is used to treat genetic diseases such as severe combined immunodeficiency (SCID), a heritable, recessive disease in which children are born with severely compromised immune systems. One common type of SCID is due to the lack of an enzyme, adenosine deaminase (ADA), which breaks down purine bases. To treat this disease by gene therapy, bone marrow cells are taken from a SCID patient and the ADA gene is inserted. This is where viruses come in, and their use relies on their ability to penetrate living cells and bring genes in with them. Viruses such as adenovirus, an upper respiratory human virus, are modified by the addition of the ADA gene, and the virus then transports this gene into the cell. The modified cells, now capable of making ADA, are then given back to the patients in the hope of curing them. Gene therapy using viruses as carrier of genes (viral vectors), although still experimental, holds promise for the treatment of many genetic diseases. Still, many technological problems need to be solved for this approach to be a viable method for treating genetic disease.

Another medical use for viruses relies on their specificity and ability to kill the cells they infect. Oncolytic viruses are engineered in the laboratory specifically to attack and kill cancer cells. A genetically modified adenovirus known as H101 has been used since 2005 in clinical trials in China to treat head and neck cancers. The results have been promising, with a greater short-term response rate to the combination of chemotherapy and viral therapy than to chemotherapy treatment alone. This ongoing research may herald the beginning of a new age of cancer therapy, where viruses are engineered to find and specifically kill cancer cells, regardless of where in the body they may have spread.

A third use of viruses in medicine relies on their specificity and involves using bacteriophages in the treatment of bacterial infections. Bacterial diseases have been treated with antibiotics since the 1940s. However, over time, many bacteria have developed resistance to antibiotics. A good example is methicillin-resistant Staphylococcus aureus (MRSA, pronounced &ldquomersa&rdquo), an infection commonly acquired in hospitals. This bacterium is resistant to a variety of antibiotics, making it difficult to treat. The use of bacteriophages specific for such bacteria would bypass their resistance to antibiotics and specifically kill them. Although phage therapy is in use in the Republic of Georgia to treat antibiotic-resistant bacteria, its use to treat human diseases has not been approved in most countries. However, the safety of the treatment was confirmed in the United States when the U.S. Food and Drug Administration approved spraying meats with bacteriophages to destroy the food pathogen Listeria. As more and more antibiotic-resistant strains of bacteria evolve, the use of bacteriophages might be a potential solution to the problem, and the development of phage therapy is of much interest to researchers worldwide.

​​​​​​ Summary

Viruses cause a variety of diseases in humans. Many of these diseases can be prevented by the use of viral vaccines, which stimulate protective immunity against the virus without causing major disease. Viral vaccines may also be used in active viral infections, boosting the ability of the immune system to control or destroy the virus. A series of antiviral drugs that target enzymes and other protein products of viral genes have been developed and used with mixed success. Combinations of anti-HIV drugs have been used to effectively control the virus, extending the lifespans of infected individuals. Viruses have many uses in medicines, such as in the treatment of genetic disorders, cancer, and bacterial infections.


Watch the video: Πώς το σαπούνι σκοτώνει τον κοροναϊό ; (December 2021).