# 4176
Figuring out why influenza is (primarily) a winter disease has been a goal for scientists for many years. There are a number of theories out there, but the science – while not non-existent – has been a bit sparse.
Over the years we’ve touched on this subject a number of times.
In October of 2007, a study appeared in PLoS Pathogens entitled Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature by Anice C. Lowen, Samira Mubareka, John Steel, and Peter Palese. I covered this story in a blog called Cold And Dry Statistics.
Using a guinea pig as a model host, they showed that airborne spread of the influenza virus was at least partially dependent upon both ambient relative humidity and temperature.
The link was significant, but not overwhelming.
A little more than a year later, a study appeared in PNAS (Proceedings Of the National Academy of Sciences) that took another look at the data and found an even stronger correlation between the AH (Absolute Humidity) and the survival, and transmission of the virus., entitled:
Absolute humidity modulates influenza survival, transmission, and seasonality
Jeffrey Shaman, Melvin Kohn
I wrote about that study last February in It's Not So Much The Heat, It's The Humidity.
Today Jeffrey Shaman from Oregon State University, returns with the aid of 4 other researchers, to correlate the incidence and spread of influenza in the human population with the levels of absolute humidity.
This admittedly math and statistics heavy paper appears in:
A moderated collection for rapid and open sharing of useful new scientific data, analyses, and ideas.
I’ve just posted the abstract (slightly reformatted for readability). The entire article is freely available at the link below.
Absolute Humidity and the Seasonal Onset of Influenza in the Continental US
By Jeffrey Shaman, Virginia Pitzer, Cecile Viboud, Marc Lipsitch et al (5 authors)
Much of the observed wintertime increase of mortality in temperate regions is attributed to seasonal influenza. A recent re-analysis of laboratory experiments indicates that absolute humidity strongly modulates the airborne survival and transmission of the influenza virus.
Here we extend these findings to the human population level, showing that the onset of increased wintertime influenza-related mortality in the United States is associated with anomalously low absolute humidity levels during the prior weeks. We then use an epidemiological model, in which observed absolute humidity conditions temper influenza transmission rates, to successfully simulate the seasonal cycle of observed influenza-related mortality.
The model results indicate that direct modulation of influenza transmissibility by absolute humidity alone is sufficient to produce this observed seasonality. These findings provide epidemiological support for the hypothesis that absolute humidity drives seasonal variations of influenza transmission in temperate regions.
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