Posted on 02/20/2009 12:40:21 AM PST by neverdem
Winter is flu season in the world's temperate regions, but scientists still aren't sure why. Now, it turns out that the answer may have been staring them in the face all along. A reanalysis of data from past studies suggests that low absolute humidity--not low relative humidity, the factor many scientists have studied--helps the virus survive and the flu spread.
Explanations abound for why flu is king in winter, only to disappear come summer. Researchers have suggested that the virus might survive better in colder temperatures, that people are more exposed when huddled indoors, and that lower melatonin and vitamin-D levels can weaken immune systems. Humidity has also been implicated. Indoor heating makes the air in many homes drier, and several studies have shown that the virus survives better, and is more easily transmitted, when there's less moisture in the air.
As a measure of air moisture, researchers have always taken relative humidity, which is the ratio of actual water content in the air to the maximum possible level. That maximum increases exponentially with temperature, however; a 75% relative humidity at 25°C means much more vapor in the air than at 5°. Climate physicist Jeffrey Shaman of Oregon State University in Corvallis and epidemiologist Melvin Kohn of the Oregon Health Department in Portland believed that what might matter more to the virus is absolute humidity--especially because the evidence for the impact of relative humidity was never all that strong.
The duo first reanalyzed data from a 2007 paper in PloS Pathogens by Peter Palese of Mount Sinai School of Medicine in New York City and his colleagues, who found that virus transmission between two guinea pigs housed in neighboring cages falls as relative humidity rises (ScienceNOW, 19 October 2007). The link was only marginally statistically significant.
When Shaman and Kohn performed a similar analysis using absolute humidity--which is easy to calculate if you know the temperature--they found a much stronger correlation. Then, the researchers reanalyzed the data from several other studies on virus survival and transmission, by Palese's group and others, including some over 40 years old. They found the same pattern, they report online today in the Proceedings of the National Academy of Sciences. Shaman says he has no idea why other researchers never looked at absolute humidity. "Maybe it's because they always see the local weatherman talking about relative humidity," he says.
Palese read the paper at Science's request but declined to comment on it. Raymond Tellier, a microbiologist at the Hospital for Sick Children in Toronto, Canada, says the work is promising but that new studies are needed to confirm it. "In order to make the point definitively, you'd really like to see more data points," he says.
Shaman and Kohn say the data bolster the idea, suggested previously by others, that increasing humidity in nursing homes and emergency rooms might help prevent flu among vulnerable patients. Tellier agrees, but he warns that this might boost the numbers of other pathogens, such as molds.
Reason for the Season
ScienceNOW 2007 (1019), 2.
Absotively.
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This is like the realization moment at the end of the Andromeda Strain.
The answer is painfully evident but hard to believe. Most of these studies are funded by drug companies. Drug companies do not want to find natural solutions which will lower their available market of potential buyers. If humidity levels cause flu and if people knew this and if people and companies controlled humidity levels better to reduce the incidence of flu then the customer base for flu shot recipients, over the counter medicines etc would have a negative impact on the bottom line.
I think that if more scientists looked at the footnotes in the studies done by big drug companies and their nonprofits and looked at the mention of other marginally statistically significant anomalies that they would find more truths hidden from us.
Posilutely.
Would you trust an epidemiologist who consults with a Shaman? ;^)
I suspect the increased humidity levels assists the body in naturally retaining moisture in mucous membranes. Nasal passages and sinus passages do not dry out or become clogged with hardened material as much in higher humidity environments than arid environments.
When such hardening occurs in sinus passages, the surface area of the natural filter media is reduced, resulting in a higher concentration of pathogens in those filters still functioning.
I suspect there are lots of moms out there who have known about this for many years, nicely explaining why so many parents install humidifiers in their toddler’s bedroom, and why most humidifiers at Target are shelved next to baby cribs.
I suffer badly in dry conditions. Sinuses and the skin on my hands, where I have excema.
I have three humidifiers running right now in my apartment, in an effort to keep the relative humidity above 36%, which seems to be my break-even point.
In contrast, my office is at 16% relative right now. Since coming to work an hour ago, I have developed a sore throat, my lips are drying and threatening to begin cracking and I have developed a mild sinus headache. The skin on my hands has roughened and has begun to be painfully dry. I’ve consumed about a quart of water in the past hour, so it can only be attributed to the dry air.
I feel much healthier at home in controlled humidity than I do at work where it is very dry.
Humid radiator heat was better.
A few years ago I saw a study about the survival of pathogens on different surfaces, but haven’t been able to find it since. Another study found that open windows creates far better air circulation than does air conditioning, and thus eliminates pathogens faster from the air.
It seems to me that an equation could be created to determine “how healthy” a room might be, by putting it all together.
Temperature, humidity, relative humidity, type of surfaces (including antiseptic surfaces, some paint coatings are being made that are antiseptic), type of surfaces that are frequently contacted by hand, such as telephone handsets, door knobs, etc. Then air circulation could be measured, and finally judged against the “threat” pathogens.
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