Cold, dry conditions and humid, rainy climates both boost flu virus

With the current seasonal flu epidemic appearing to wind down, scientists published a report that identified two types of environmental conditions that are associated with flu epidemics, one that's cold and dry and the other being a humid and rainy climate.

The researchers at the National Institutes of Health's Fogarty International Center found that temperature and specific humidity, which is different from the relative humidity most people are familiar with, are the best individual predictors of the months of maximum influenza activity, according to a news release from the NIH.

A cold and dry climate encourages the virus' reproduction and expulsion in infected animals, as well as the virus' stability in the environment. That, in turn, increases the probability of transmission, according to the release.

The reasons why humid and rainy environments encourage the spread of the flu are not known, though some speculate it's because people are more likely to be indoors during the rainy season or in a rainy region. More research is suggested.

The current flu season by some gauges is still in an epidemic but indicators point to it being close to over, according to new data from the Centers for Disease Control and Infection.

For the week ended March 2, 17.2% of flu tests were positive, down from a peak of 38.5% during the last week of 2012, according to the CDC.

The CDC also reported that no states have high levels of influenza-like illness activity. Four states had moderate flu-like illness activity, thirteen had low activity and 33 had minimal activity.

Still, the percentage of all deaths attributed to the flu and pneumonia stood at 7.7%, just above the epidemic threshold of 7.5% for the week ended March 2.