Influenza outbreaks linked to low “absolute” humidity levels

February 10th, 2009 - 1:51 pm ICT by ANI  

Washington, Feb 10 (ANI): Ever wondered why we catch flu mostly in the winters? Well, Oregon researchers claim to have found the answer.

They have found that influenza virus survives and travels best when “absolute” humidity is low.

According to lead author Jeffrey Shaman, an Oregon State University, It has long been suspected that there is a link between humidity and flu transmission and prevalence; however, these efforts have focused on relative humidity.

During the study the researchers analysed data from a 2007 study published in PLoS Pathogens, which found a tenuous relationship between influenza transmission and relative humidity.

Shaman used the team’’s research data and substituted absolute humidity for relative humidity in analysing potential correlations with flu transmission.

“The correlations were surprisingly strong,” Shaman said.

“When absolute humidity is low, influenza virus survival is prolonged and transmission rates go up, he added.

The researchers showed that relative humidity only explains about 36 percent of influenza virus survival.

The Oregon researchers retested the data using absolute humidity and found a dramatic rise in accounting for both transmission (50 percent, up from 12 percent) and survival (90 percent, up from 36 percent).

The transmission rates increased from 12 pct to 50 pct while the survival increased to 90 percent from 36 percent.

The potential explanations for influenza peaks during the winter in temperate regions are that people spend more time indoors and thus transmit the virus more easily;

Moreover, less sunlight may have a chemical effect on the virus and/or people’’s immune response or there might be an unknown environmental control.

“In some areas of the country, a typical summer day can have four times as much water vapour as a typical winter day a difference that exists both indoors and outdoors,” Shaman said.

“Consequently, outbreaks of influenza typically occur in winter when low absolute humidity conditions strongly favour influenza survival and transmission,” he added.

The results are published in the Proceedings of the National Academy of Sciences (PNAS). (ANI)

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