At this time we have many questions about the H1N1 flu pandemic. Quinnipiac Associate Professor and Immunologist Lisa Cuchara, Ph.D. answers some frequently asked questions about H1N1…For example, we are being handed Purell bottles everywhere. Are they effective?
Q: How does Purell claim to "kill" viruses, when viruses are not alive?
A: True, viruses are not technically "alive" so they cannot be "killed", but technically the sun does not "set" or "rise" either and yet we still say that. Viruses can become "inactivated" rather than “killed”.
Q: How does Purell kill bacteria and viruses? Does the alcohol (or other ingredients) do something to the protein coat?
A: Alcohol "kills" by denaturing proteins (kind of like frying an egg changes the proteins).
Q: Can microbes develop resistance to Purell and other alcohol based hand sanitizers?
A: The mode of action of alcohol against bacteria and viruses is physical rather than chemical or biochemical. Just as it would be very difficult for a microbe to develop resistance against fire it would be very difficult for a microbe to develop resistance against alcohol. The CDC does recommend the use of hand sanitizers, especially when you cannot use soap and water to wash your hands, in the fight against infectious diseases such as the flu. In contrast to alcohol-based hand sanitizers, bacteria CAN develop resistance to anti-bacterial soaps with active ingredients such as Triclosan, Alkyl Dimethyl Benzyl Ammonium Chloride, Dimethyl Ethylbenzyl Ammonium chloride, Benzethonium Chloride, or Benzalkonium Chloride (found in antibacterial handwipes and antibacterial soaps). These low concentration of these agents (as compared to hospitals were they are used at much higher concentrations) contributes to the ability of bacteria to develop resistance to these agents. Studies have shown that “soaps containing Triclosan within the range of concentrations commonly used in the community setting (0.1%–0.45% wt/vol) were no more effective than plain soap at preventing infectious illness symptoms and reducing bacterial levels on the hands”.
Q: Does Purell kill all kinds of bacteria and viruses equally?
A: Alcohol will "inactivate" most viruses, some easier than others. Viruses have RNA or DNA inside and then a protein coat outside. Some viruses (enveloped viruses) have a lipid layer (from budding from the cell). Enveloped viruses such as influenza virus, herpes simplex virus, HIV, respiratory syncytial virus (RSV), vaccinia virus, hepatitis B, hepatitis C viruses are very susceptible to alcohol. Non-enveloped viruses (hepatitis A, enteroviruses -- both cause gastrointestinal viruses) are harder to "kill" and require higher concentrations of alcohol and longer exposure times.
Q: Are all concentrations of alcohol equally effective?
A: No, alcohol only works at the right concentration. 100% evaporates too quickly to be effective and low concentrations do not work at all, 60-90% is best. There used to be some 25% and 40% out there in stores but I have not seen anything lower than 62% in the past two years.
Q: Does Purell replace the need for washing with soap and water?
A: No. You should wash your hands with soap and water (for 20 seconds) when your hands are visibly soiled, after going to the bathroom, etc. Alcohol-based sanitizers such as Purell should be used when you cannot wash with normal soap and water or in certain settings when washing with soap and water becomes either cumbersome and irritating, such as certain health care situations. The transient bacteria and viruses that you come in contact with via shaking hands, touching doorknobs, shopping carts, etc. are effectively removed with proper hand washing or hand sanitization.
Q: Lysol claims that it kills 99.9% of Influenza A viruses - how?
A: The active ingredients in Lysol are quaternary ammonium compounds (QACs). QACs binds to the lipid envelope and inactivates the protein coat making the virus non-infectious. Lysol has been proven to kill a variety of viruses and bacteria. Bacteria cell walls are negatively charged thereby “attracting” QACs which are positively charged cations. QACs adsorb onto the bacterial cell surface, diffuse through the cell wall and once inside bind to the cytoplasmic membrane causing disruption and death.
Q: How long can influenza virus remain viable on objects (books, doorknobs, etc.)?
A: Studies have shown that influenza virus can survive on environmental surfaces and can infect a person for 8 hours after being deposited on the surface. Studies have shown that doorknobs, shopping carts, vending machines, remote controls and other common use objects have more bacterial than most public rest rooms (because the latter are cleaned regularly). Be aware when touching these objects and try not to touch your face, rub your eyes or nose or eat. The viruses and bacteria on your hands
do NOT give you the flu, these pathogens need to come in contact with mucous membranes (typically those in your mouth, nose and eyes) in order to infect you.
Q: What surfaces are most likely to be sources of
contamination?
A: Germs can be spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth. Germs can be spread when a person touches respiratory droplets from
another person on a surface like a doorknob or desk and then touches their own eyes, mouth or nose before washing their hands.
Q: What are the signs and symptoms of this virus in people?
A: The symptoms of 2009 H1N1 flu virus in people include fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and fatigue. A significant number of people who have been infected with this virus also have reported diarrhea and vomiting. Severe illnesses and death has occurred as a result of illness associated with this virus.
