Climate factors influence seasonal influenza activity in Bangkok, Thailand

Analysis by GLM suggests that increased influenza activity occurred twice a year (Fig 3). The first and smaller wave of increased influenza activity was in February, which corresponds to the beginning of hot and dry weather. The second and larger influenza wave occurred between August and September, which coincides with the second half the rainy season. Both periods represented increased influenza A(H1N1)pdm09 and influenza B virus activity. Mean- while, influenza A(H3N2) activity was only associated with the second wave, which coincided with higher relative humidity and rainfall and occurred approximately 5 months after the first influenza A(H1N1)pdm09 peaked. As expected, GLM showed no association between influ- enza activity and temperature. Fig 2. Incidence of influenza virus relative to meteorological factors. Monthly mean temperature (A), relative humidity (B), or rainfall (C) (shaded gray) are shown with the confirmed cases of influenza A(H1N1)pdm09 virus (purple), influenza A(H3N2) virus (yellow), influenza B virus (blue), and all influenza viruses (dashed line). Scale on the right Y-axis denotes the percentage of the influenza virus-positive samples each month. Dotted horizontal line indicates the overall average temperature (28.73˚C), relative humidity (73.32%), and rainfall (9.11 cm3) over nine years (left Y-axis). https://doi.org/10.1371/journal.pone.0239729.g002 PLOS ONE Climate factors influence seasonal influenza activity in Bangkok, Thailand PLOS ONE | https://doi.org/10.1371/journal.pone.0239729 September 29, 2020 6 / 15