Effect Measure

Flu, handwashing and disinfecting the world

Most people are either indifferent to swine flu or fearful, but the makers of Purell hand sanitizer and Chlorox are happy. It’s been a boon to the business of sanitizing everything in sight as a way to ward off swine flu. Here’s a story about Chlorox (bleach):

The company has secured additional suppliers and will increase production if needed, says Benno Dorer, senior vice president- general manager of Clorox?s cleaning division. Some retailers have already asked for more bleach, he said in a Sept. 4 telephone interview, declining to name specific companies.

An outbreak of the flu may add 2 percent or more to Clorox?s per-share earnings for the duration of the outbreak, says Ali Dibadj, a New York-based analyst with Sanford C. Bernstein & Co. That benefit isn?t reflected in Clorox?s shares or analysts? projections, he said.

?Sales of bleach and wipes, which are about a quarter of Clorox?s profit, could grow in the high single digits or more,? Dibadj said in an e-mail. ?It depends on how severe the outbreak might be, but the fear of an outbreak is enough.?

[snip]

Bleach shipments increased in the U.S. and Latin America during the quarter ended June 30, Dorer said.

?There is a clear correlation to those sales and concerns about H1N1,? Dorer said. He declined to say if sales in the current quarter had risen due to swine flu.

Clorox hasn?t increased inventory because it can quickly boost production at any of its seven U.S. bleach- related plants, Dorer said. Most products can go from factory to retailer in a week, he said.

The company is working closely with the WHO, the American Red Cross and the CDC, he said. Clorox donated 18,000 cases of bleach to relief and government agencies during the first swine flu outbreak, he said.

?We?re prepared to do that that again if the need arises,? Dorer says. (Clean link)

One of the things that surprises people the most about what we know about influenza is what we don’t know. One of the things we don’t know is the principal mode of transmission of flu. It’s probably one of three: large droplets that fall out quickly and don’t remain suspended; much smaller aerosols of virus-laden particles that remain suspended in the air for hours or even days; and flu that’s on inanimate objects (known as fomites). We’ve discussed the first two modes pretty often here (examples here and here) and they have a direct bearing on things like what kind of mask might or might not work. We still don’t know the answer. The third mode, inanimate objects, is what hand sanitizers and Chlorox bleach are all about.

Obviously if your hands are laden with virus because you cough or sneeze into them, it’s good to sanitize your hands. But the evidence that you can get flu from virus particles you pick up from a doorknob, desk top, keyboard or even someone else’s uncoughed-on hands is pretty meager. In fact, it’s almost non-existent. So why do all the public health authorities, including CDC, keep telling people that the best defense is to wash your hands? That’s the question that Dr. Arthur Reingold, head of epidemiology at the University of California, Berkeley, and codirector of the CDC-funded California Emerging Infections Program wanted to know. So he sent a letter to CDC asking it:

Dr. Anne Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases, says the CDC’s emphasis on hand-washing is guided by the “science that supports hand-washing against respiratory infections in general.” In particular, she cites a study conducted in Pakistan that showed that hand hygiene measures cut the rate of pneumonia in half. One of the unique features of swine flu?the fact that it causes diarrhea?also suggests to some that it could be transmitted on the hands like other diarrhea-causing diseases that do not belong to the influenza family. Schuchat stresses that the best way to protect yourself will be to get the vaccine once it becomes available in October, but adds that the CDC continues to believe that “contact precautions are useful with this flu.” (Newsweek)

Most epidemiologists agree that hand hygiene plays a part in a number of diseases, both respiratory and intestinal. It’s good to have clean hands as a general principle. You can over do it, of course, and overdoing it is something germ-phobic Americans are pretty good at. But, yes, wash your hands. This doesn’t answer Reingold’s question, however. Evidence for contact infection specifically for influenza is very, very hard to come by. But we keep hearing it. Why?

We will hazard two answers. The first is that many of the people at CDC and in health departments say it because they think it’s true. They don’t really know the scientific evidence for it. They think it’s there, even though it isn’t. Mistatements of facts by authorities isn’t so uncommon. Even CDC’s Dr. Schuchat, who is really a skilled and credible spokesperson on flu for her agency, continues to say that seasonal flu kills 36,000 people every year, even though that is misleading and wrong. All she has to do is say, “our experience over many flu seasons, is that on average there are some 30,000 – 40,000 extra deaths we believe wouldn’t have happened if the people hadn’t gotten the flu. Some years it’s much more, some years it’s much less.” Or some such thing. It’s both clearer and easier to understand. It also has the virtue of being what we think is actually the case.

Which brings us to the second reason CDC and state public health officials repeat the handwashing mantra. They not only believe it, but in fact without a vaccine they have nothing much else to offer. Giving people something to do affords a feeling of empowerment, which is also probably a good thing. The power they think they have (literally) in their hands might not be real, but it is comforting for most of us to think there is something we can do. And of course for public health officials, who are always being asked by the public what they should do, it’s nice to have something to say, something that doesn’t even require anything from the public health system. Like any placebo, it works best when both the patient and the doctor believe it works.

Or maybe not. Maybe it’s like Niels Bohr’s famous answer to the reporter when asked why he had a lucky horseshoe over the lab bench: “You don’t believe it will bring you good luck, do you Professor?” “No,” Bohr replied. “But I understand it works even if you don’t believe in it.”

Comments

  1. #1 mk
    September 18, 2009

    “But the evidence that you can get flu from virus particles you pick up from a doorknob, desk top, keyboard or even someone else’s uncoughed-on hands is pretty meager.”

    “Evidence for contact infection specifically for influenza is very, very hard to come by.”

    Why is this? As a non-scientist/medical person, I don’t understand how this cannot be known today… the 21st Century. Have there been no tests specifically designed to learn these things? Can’t we just smear influenza on a doorknob, have someone grasp it and check to see what happens? Forgive me if that’s really a silly, elementary question.

    Many thanks.

  2. #2 revere
    September 18, 2009

    mk: For good or ill, we are limited in the kinds of experiments we can do on people. We know many things about flu in the environment: that replicable viral particles can last for a long time on nonporous objects (hours, days, even weeks); that the same particles may only remain replicable for 5 minutes on a human hand; that there is flu virus RNA floating in the air of an emergency room, etc. But human infection and its transmission is very complicated and has many moving parts. Does genetic material floating in the air of an emergency room mean you can be infected? It may be just parts of viral fragments. It may be that for most people to get infected you need a certain minimum inoculum you almost never get from touching a doorknob. Then there are the host and environmental factors. Maybe it only happens under certain conditions of temperature and humidity, or only in certain age groups or people with certain immune status, etc., etc. And we know that there are multiple ways to pass flu from person to person. So the overarching question becomes, in the real world, what are the most common or most important ways that flu is transmitted? A flu virus has only 8 genetic segments and maybe 11 genes. Yet we still don’t know what makes it transmissible, what determines host specificity, why it is seasonal and many other things you’d think we’d know. And when you start to delve into the science, you will see how complicated it is. Go to the sidebar categories and click under Bird flu, subcat, biology.

  3. #3 mk
    September 18, 2009

    Thanks again, very helpful.

    I genuinely love “delving” into more info, so I’m looking forward to the sidebar you directed me to!

    Cheers.

  4. #4 Mark
    September 18, 2009

    Thanks Revere for this interesting post regarding Swine flu transmission. Regarding Chlorox, during WWII Chlorox produced a civil defense film for the US government – What to Do In Case of a Gas Attack (1942). One of the decon actions recommended is to wash the skin with straight bleach. A short (1:44s) clip from the film is posted to:
    http://www.youtube.com/watch?v=DMczp_YuJXo&feature=channel_page

  5. #5 melbren
    September 18, 2009

    Speaking of what we don’t know….

    I just read yesterday that Richard Shope, the man who first identified the 1918 influenza as a virus, and correctly attributed it to swine, also held a very “controversial” belief. He apparently believed that the difference in virulence between the first and second wave of the 1918 flu, was the virus’ tendency to associate with a nasty bacteria that fall. He did not believe a more virulent strain of swine flu emerged in September–he believed the swine flu remained unchanged. Shope was convinced that the difference between the Spring and the Fall of 1918 was not a change in the flu–it was the addition of a nasty bacteria in the Fall of 1918.

    I am concerned that we are experiencing this now–but we’re not “seeing” it.

    Just look around–most people who are sick with swine flu-like illnesses right now (who probably do indeed have swine flu) have symptoms that are also consistent with strep. But they are not being prescribed antibiotics. Doctors are telling my friends and family one of two things: “it’s just the flu–you get a sore throat with flu” or “the strep test was negative–so it must be viral.“ (How reliable are rapid strep tests?–I honestly don‘t know.)

    Thanks to Revere, I learned early on that it is the secondary bacterial infection that is so dangerous in the swine flu experience–but I pictured a pneumonia. I was not picturing strep. And the idea of strep being dangerous right now really resonates with me–“strep” is somehow less of an abstraction than “pneumonia.”

    And I think the messaging right now ought to include some sort of re-branding of swine flu that specifically references a bacteria. How about, “The swine flu is mild–not much worse than seasonal flu–but it’s the strep that will do you in.” That will get everyone’s attention! Because typical people (like me) and typical doctors (un-like Revere) are not understanding this. We are not “respecting the strep.”

    The human respiratory tract is not the same environment that it was two or three months ago. The human respiratory tract needs to be more vigorously defended for the next few months. It sounds to me like the swine flu has the tendency to make the human respiratory tract–upper and lower—more hospitable to bacteria like strep. It makes sense that those who usually don’t get strep are more likely to get it right now, and for those who tend to get strep–they may be about to have a more severe infection than usual. And a severe bacterial infection, untreated by antibiotics, can kill.

    My family is facing a very serious situation right now with my 26 year old cognitively disabled niece who was very cavalierly dismissed by an urgent care center earlier this week due to a negative rapid strep test. It seems that nothing about the system worked the way it should have.

    I was able to intervene and advocate on my niece’s behalf only because of the excellent information that I have been provided with and/or have been linked to via Effect Measure over the past few months. Had I not aggressively questioned her care…(I can’t even go there.) But thanks Revere, and Effect Measure community.

    And, by the way–if we’re not going to be prescribing antibiotics for the bacterial infections that arise over the next few months–we might want to mention that to people are not planning on having their children vaccinated. They need to be forewarned that there might not be a back-up plan. Especially if they are poor. (because we’re apparently a lot more concerned about “herd immunity” issues when the patient in need of antibiotics is poor.)

  6. #6 ecologist
    September 18, 2009

    This is an interesting discussion. There is a subtle but important distinction between considering handwashing from the medical point of view, focused on the individual, and from the epidemiological point of view, focused on the population. The rate of spread of an epidemic is determined by the net reproductive number R_0 (the expected number of new infections produced by a single infected individual in an otherwise susceptible population). R_0 depends, among other things, on the rate of transmission from individual to individual. Even small changes in the probability of transmission can have important effects at the population level in the rate of spread and the eventual level of infection. [That's why influenza outbreaks track school vacations ... it's not that going to school is bad for you, it's that a population of children in a setting that reduces contact will produce a lower R_0.] The changes in the probablity of transmission produced by handwashing could be hard to detect, or appear trivial, at the individual level, and still have a significant effect at the population level.

    There is also a second level of population effect, which is inherently impossible to detect in a medical study. If R_0 is reduced, the level of infection in the population will be reduced, which will reduce the rate of infection of susceptible individuals. But that reduction will affect both handwashing and non-handwashing individuals alike (assuming that they are equally mixed in the population), and so cannot be detected by any clinical study of handwashing within a single population.

    I suspect that part of the reason that CDC recommends handwashing is that they are concerned with epidemiology as well as individual medicine.

  7. #7 Curious
    September 18, 2009

    Melbren’s comment is interesting. I’m looking forward to seeing comments on it.

    We’re regular users of hand sanitizer (now), mainly because I don’t trust my kids to do the requisite 30 second scrub. Before swine flu, you would have never caught me carrying a bottle of it, though. Despite the practice, it sure doesn’t feel like much of a defense to me, especially since three of us came down with colds this week despite the extra vitamins, sunshine, hand-washing, etc.

    In any case, I have a question: Do the deaths in this chart http://www.cdc.gov/h1n1flu/updates/us/ reflect JUST flu deaths and flu related pneumonia deaths? Or do they include all pneumonia deaths in general (as in the case of an elderly person who didn’t have the flu, for instance). Because 364 H1N1 deaths in one week? That’s alarming.

  8. #8 Phila
    September 18, 2009

    And of course for public health officials, who are always being asked by the public what they should do, it’s nice to have something to say, something that doesn’t even require anything from the public health system. Like any placebo, it works best when both the patient and the doctor believe it works.

    I wonder if it also serves as a reminder for some people? Maybe people who are careful to wash their hands are also more likely to cover their coughs, stay home when sick, and so forth? I think these things are easier to do as part of an overall routine.

    My wife works with small children, and I know she became more immediately conscious of these issues once her client families started buying sanitizer in response to swine flu.

  9. #9 rpsms
    September 18, 2009

    @#7: Perhaps the new reporting system the table references has an impact on the number of reports.

  10. #10 SusanC
    September 18, 2009

    Revere, you’re right. They say it because they think it’s true, and/or because they think it makes people happy.

    Both are (marginally) excusable reasons, but still someone needs to point out what science tells us. Or does not. Thanks for doing it!

  11. #11 Vincent Racaniello
    September 18, 2009

    Influenza is clearly transmitted by contact in the guinea pig. And the virus can remain infectious on inanimate objects. I agree that the gap needs to be filled with experiments in humans but until we know the answer it seems we should err on the safe side.

  12. #12 revere
    September 18, 2009

    Vincent: In the guinea pig, it is transmissible in both droplet and contact experimental set-ups. If it were only the contact set-up one might make a stronger case that the contact cage wasn’t droplet instead. Regarding viral particles staying replicable on inanimate objects, it is certainly true that has been shown. But replicability isn’t disease transmission. Nor does it remain replicable long on the hands. So if someone sneezes or coughs into their hands, shakes your hand and then you put your hand to your nose or eye, there is a good chance you could infect yourself (which is what I said in the post). But the real question is what happens in the real world. As we infect each other, how much of it is via fomites, droplet or suspended particles. That question has not been answered and there is little or no epidemiological evidence of transmission via fomites. That’s the uncomfortable fact that Art Reingold pointed out and he’s correct.

    I’m in favor of good hand hygiene. But I’m also in favor of being clear eyed about things here. Good hand hygiene has been shown to be related to better respiratory disease experience and certainly intestinal disease. But there is little evidence for flu, despite years of looking for fomite outbreaks. They just don’t seem to happen in the real world, at last that we’ve been able to see.

  13. #13 ssal
    September 18, 2009

    Revere:

    Just to make sure I’ve got it straight.

    The following is the much more accurate statement:
    “Scientists have in fact looked hard (with good, controlled experimentation) over the years for significant flu transmission due to inadequate hand hygiene, but can’t find it.”

    And the following is much less accurate:
    “A lot of flu transmission may well be taking place due to inadequate hand hygiene, but it may be that scientists just haven’t done enough experimentation to show it is happening.”

    (Please feel free to put forth what you think would be the best concise statement on that matter.)

  14. #14 revere
    September 18, 2009

    ssal: Here’s what I believe to be an accurate statement. There is almost no epidemiological evidence (including outbreak investigations) that flu has been transmitted from person to person via an inanimate object.

  15. #15 miso
    September 18, 2009

    Well if you believe resistance to Tamiflu was/is/will be a result of overuse and at incorrect dosage and not because Roche and the FDA were in a hurry to test and market Tamiflu in the U.S. to cash in before Relenza established and expanded it’s range(iv zanamivir, an atomized inhalant, and LANIs were being developed in the 90′s but ran out of funds against Tamiflu). Tamiflu was FDA approved despite the unexplored consequences of no resistance to H274Y in seasonal influenza discovered in it’s earliest clinical trials.

    The media should be warning that overuse and incorrect concentration of hand sanitisers and bleach will cause resistance, shouldn’t they?

  16. #16 miso
    September 19, 2009

    Where’s all the evidence that Tamiflu and Relenza resistance is spontaneously generated*, and doesn’t match resistant strains that were to be found in laboratories years ago; strains that have been studied down to atomic structure, chemical bonding behaviour and mechanisms of resistance.

    This influenza pandemic era isn’t going well for us because so little honest science is being done and reported.

    * (a pre-AD theory, re-introduced by the Roche PR team to explain Tamiflu resistant flu strains)

  17. #17 lugon
    September 19, 2009

    I’ve started a thread over at newfluwiki2.com http://newfluwiki2.com/diary/3958/appropriate-handwashing with 2 nice videos.

    It’s obvious hand-washing has a role to play in public health. For a number of diseases, and all over the world. If this pandemic is an opportunity to push that into public concience, so be it.

    Now, how much it will change things in this pandemic, particularly when done in schools where kids stand in line in large numbers? We’ve chosen, wisely in my view, not to dance the proactive student dismissal dance.

    If you ask me, it’s partly because there has not been enough public rehearsal of how such a dance would have been done. So we haven’t identified ways to mitigate mitigation. That way, mitigation stays expensive, and we don’t even want to think about it. (I said it’s partly because of that. It’s also because really, this pandemic is currently a Cat 1, so schools shouldn’t close, or should they.)

    Anyway, we’ve chosen not to send students home. They are getting close to each other and, surprisingly, they don’t stop breathing when they do that. So transmission _is_ happening. Unsurprisingly.

    Simply because if we breathe near each other with clean hands, transmission happens.

    And we may be making things worse when we tell students to queue up to wash hands. Has anyone run the numbers on how many students per bathroom there are in the US or elsewhere? How long are the queues? Or are they using the “appropriate technology” devices I suggest in the above link, with videos included?

    I wonder what people will believe about Public Health when they find that transmission happens anyway. Will they adjust their mental models and think “Ah, well, it might have been worse?”. We do that as individual patients, “I was lucky to have my leg amputated” or whatever, so it _may_ happen.

    Messy, messy world! ;-(

  18. #18 kimw
    September 20, 2009

    Thank you for this blog entry, revere, which is destined to “go viral.” I dislike the nation’s public health agency frequently advocating an activity to stymie the spread of influenza when it knows that hand-washing may very likely have nothing to do with flu transmission. Just to give me “something to do.” I want science from a science agency, not placebos. And not paternalism, either.

    Not that hand-washing is a horrible thing, and as you pointed out, certainly does matter in the transmission of some bacterial infections (I recall reading once about the fecal count in reach-in ice dispensers…yeech). Nevertheless, if the CDC wants to soothe our fears, the last thing they want to do is be found guilty of obfuscating on prevention. I’m sure most people have gotten the message that hand-washing is one proven means to halt the spread of flu. I feel less safe now having learned that the CDC sometimes hands out placebos to the public, rather than genuine, pertinent information.

  19. #19 g336
    September 24, 2009

    Whether or not handwashing does any good preventing the spread of flus, it prevents the spread of diarrheal diseases, and that by itself is sufficient reason to encourage it.

    We do not want people getting the idea that they don’t need to wash their hands, as then we’ll see an increase in intestinal diseases and in flu coinciding with same. The latter may make the intestinal symptoms appear to be part of the flu when they are not.

  20. #20 revere
    September 24, 2009

    g336: I think it’s not correct to say this is about handwashing. It’s about flu. If I said that taking enough vitamins was a good thing and we should do it to ward off the flu that might or might not be true about the flu part but still a good thing to do. Same with voting. It’s good to vote and it might help a lot of things. But we’re talking about flu, and Art Reingold, who raised the issue, raised a legit one. I’m not for encouraging magical thinking to ward off a particular disease, even if that same thinking is science based for other diseases.

  21. #21 kathy
    September 24, 2009

    Well, here is some new evidence about flu transmission, hand washing and touching your eyes nose and mouth.

    http://www.medicinenet.com/script/main/art.asp?articlekey=105689

    Mark Nicas at UC Berkeley School of Public Health just published these results last week.

  22. #22 revere
    September 24, 2009

    kathy: First, thanks for the reference. We’ll all be interested in taking a look when there is finally a paper from this. Frankly, I will say this doesn’t seem even reasonably credible to me. The large droplets are laden with virus and are the source of virus on fomites. So how is it reasonable that fomites are twenty times more likely than large droplets? There is quite a bit of epidemiologic evidence for droplets, less so for airborne, almost none for fomites. No one says it can’t happen. The question is, what are the predominant mode(s) of transmission in the real world. The idea that it is doorknobs and airplane arm rests and desktops in schools doesn’t have epidemiological support. Maybe it;s true. But I’d be pretty surprised. But these folks are presenting an argument (no data, apparently) that we should take seriously when we are able to see it.

  23. #23 Phillip Huggan
    September 26, 2009

    Just give someone with any flu ziplock bags and $1000. Have them rub their nose or cough or sneeze and then rub the ziplock bag.

    Place ziplock bags in negative air pressure hood, have paid volunteers rub the bags and touch noses, face, eyes….

    The negative pressure hoods might not even be necessary if the static snotty plastic bag doesn’t evaporate droplets. This should be easily testable.

    Not conclusive, and doesn’t help with procurement much as copper doorknobs stop staph infections and such. A much bigger test would tell you if surgical gloves are effective here and how much. Then you can use results to test respirators and surgical masks….

    C’mon people this isn’t lateral thinking. It is friggin basic.

  24. #24 Phillip Huggan
    September 26, 2009

    Chlorox and Purell sound like suitable Socially Responsible mutual fund inclusions.

  25. #25 Phillip Huggan
    September 26, 2009

    …have to wash faces and maybe reapply and wash a few times if snot sublimates droplets to any degree. Knowing the ratio of droplet to big drop to snot communicability would allow focus on what respirators and/or full face respirators and/or skin-paper/textile “glue” to develop. A $3T bailout for Baxter would’ve gone a long way here…
    But profit over survival I know the ethic all too well.

  26. #26 Skeptigirl
    September 28, 2009

    So we have multiple studies demonstrating viable flu virus can be recovered from surfaces like doorknobs for hours to days after being deposited depending on the strain/study. We have multiple studies demonstrating pathogenic respiratory viruses can infect people via contaminated hands. There is at least one study demonstrating 30% of influenza cases are spread by hand contamination.

    Shouldn’t the default position here be handwashing until proven otherwise?

    http://www3.interscience.wiley.com/journal/122466317/abstract
    “ABSTRACT

    The relative contribution of four influenza virus exposure pathways—(1) virus-contaminated hand contact with facial membranes, (2) inhalation of respirable cough particles, (3) inhalation of inspirable cough particles, and (4) spray of cough droplets onto facial membranes—must be quantified to determine the potential efficacy of nonpharmaceutical interventions of transmission. We used a mathematical model to estimate the relative contributions of the four pathways to infection risk in the context of a person attending a bed-ridden family member ill with influenza. Considering the uncertainties in the sparse human subject influenza dose-response data, we assumed alternative ratios of 3,200:1 and 1:1 for the infectivity of inhaled respirable virus to intranasally instilled virus. For the 3,200:1 ratio, pathways (1), (2), and (4) contribute substantially to influenza risk: at a virus saliva concentration of 106 mL−1, pathways (1), (2), (3), and (4) contribute, respectively, 31%, 17%, 0.52%, and 52% of the infection risk. With increasing virus concentrations, pathway (2) increases in importance, while pathway (4) decreases in importance. In contrast, for the 1:1 infectivity ratio, pathway (1) is the most important overall: at a virus saliva concentration of 106 mL−1, pathways (1), (2), (3), and (4) contribute, respectively, 93%, 0.037%, 3.3%, and 3.7% of the infection risk. With increasing virus concentrations, pathway (3) increases in importance, while pathway (4) decreases in importance. Given the sparse knowledge concerning influenza dose and infectivity via different exposure pathways, nonpharmaceutical interventions for influenza should simultaneously address potential exposure via hand contact to the face, inhalation, and droplet spray.”

  27. #27 anon
    September 28, 2009

    they just test exposure to the viruses, not whether
    the virus will actually enter cells and infect.

    putting viruses on nose-mucous is not the same as
    inhaling it into the bronchies,lungs.

    test people with flu how/how often thy touch their
    nose,eyes

    does flu enter through eyes at all ?
    say in >1% of infections

    same question for mouth

    same question for nose

    test it in volunteers
    ask people with flu, how they may have got it

  28. #28 revere
    September 28, 2009

    skepti: It is the default position and I have no problem with it. The paper you referenced, however, is not actually infections but a modeling study done with assumptions about transmission based on very uncertain data serially cascaded. No actual measurements of infection or transmission were made. Moreover it is a very special circumstance: personally attending a virally shedding person very closely over a period of days. What we don’t know is what happens in the community. It is very unlikely, IMO, that most virus is transmitted via door knobs etc. while a minority via cough droplet or airborne in the community. There is almost no evidence for this in the epidemiological literature. Transmission depends on the size of the inoculum to the susceptible host cell, among other things. Art Rheingold (and I) were raising a scientific question and CDC’s answer was that they don’t have any info on flu, specifically. You can find viruses everywhere if you look. What we don’t know, epidemiologically, is the significance in causing cases in the real world (just as you can find pathogens in cockroaches but you hardly ever find outbreaks caused by cockroaches in the literature).

    The bottom line is this: we don’t know the relative contributions of the three postulated modes of transmission (and maybe there are more; you can find flu virus in water and in food if you look). That’s because it’s very hard to make that determination. So, yes, by all means make handwashing the default. It will certainly (and with data to back it up) help with other diseases. But the idea that we know for certain that it’s the best way to prevent influenza is not well supported (I’m understating for effect).

  29. #29 Susan Solomon
    December 13, 2009

    It is unlikely that hand washing will reduce the number of cases of Swine Flu or any flu by any appreciable amount. This is true because viruses in general are far more often spread through the air or from membrane to membrane than by hand to hand touch. Even if one could prove, and it hasn’t been proven, that hand to hand touch spreads viruses, and one disinfects hands regularly, that still leaves the more likely airborne method of contagion in place. Since people are going to be exposed to viruses, and hand washing/sanitizing at best is only a dim second place means of prevention, it seems one should concentrate on understanding nutrition and biochemistry, and how to build a strong immune system. This approach was well in place all through the ages, and only in the last 20 years has it been almost entirely eclipsed by medicine. Medicine is not the last word in human health. Nutrition and organic biochemistry are. Get enough protein (0.4 X ideal body weight per day at a minimum) Get enough Vitamin A, C, D. Get enough minerals such as calcium and magnesium in the right balance. Take tons more C when sick. Get moderate fiber, esp fruit, Stay away from canola, sunflower and other unsaturated oils which have been promoted for purely profiteering reasons and are harmful to the liver. (Use olive oil and butter instead) Get plenty of rest and liquids. Etc. It comes down to personal health habits and genes. Someone is making millions on hand sanitizer, something that doesn’t even address the main means of contagion, and will not confer upon you ordinary human health, and no one disagrees with that.