Influenza peaks, specific humidity and precipitation.

<p>(A) Estimated U-shaped relationship between the likelihood of an influenza peak and average monthly specific humidity across all sites, based on logistic regression (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003194#ppat-1003194-t001" target="_blank">Table 1</a>). The left side of the curve is strongly correlated with the relationship between specific humidity and influenza survival and transmission observed in laboratory studies <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003194#ppat.1003194-Shaman3" target="_blank">[17]</a>, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003194#ppat.1003194-Shechmeister1" target="_blank">[32]</a>, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003194#ppat.1003194-Schaffer1" target="_blank">[33]</a>. However, the mechanism that causes the pattern on the right side of the curve is not readily explained. (B) The relationship between average monthly specific humidity and precipitation across all sites. Influenza peaks clustered in months associated with low specific humidity and high precipitation conditions. This suggests that precipitation may explain the occurrence of humid-rainy influenza peaks and may be responsible for the right hand side of the U-shaped curve between specific humidity and influenza (A).