Objectives The aim of this study was to investigate the impact of short-term variation of temperature and humidity on the risk of influenza-like illness (ILI).
Methods ILI monitoring data for each week from all sentinel monitoring hospitals in Guangzhou in 2010-2015 were collected from the influenza surveillance system of Guangdong Provincial Center for Disease Control and Prevention. Meteorological data of each week, including mean temperature (TM) and relative humidity (RH), in Guangzhou during the same period were obtained from Guangzhou Meteorological Bureau. Then vapor pressure (VP) was calculated with these indicators representing the absolute humidity (AH). A distributed lag non-linear model (DLNM) was used to assess the short-term (Lag 2 weeks) effect of temperature and humidity on the risk of ILI.
Results The peak season for ILI was mainly in winter, spring and summer. There was a nonlinear relationship between ILI and mean temperature. As temperature rising, the risk of ILI increased at first and then decreased. When the mean temperature was 14℃, the relative risk of ILI was the highest. Compared with the mean temperature at 25℃, the risk of ILI in 14℃ increased 0.053.8% (95%CI:0.035. 1%~0.072.6%). As the absolute humidity rising, the risk of ILI was also increased at first and then decreased. Compared with the absolute humidity at 22 mb, the risk of ILI increased 0.049.1% (95%CI:0.031.8%~0.066.4%) at 10mb. Conversely, the association between relative humidity and ILI was relatively weak. An analysis on the combined effect found that the risk of ILI was higher in low temperature and low humidity.
Conclusions Temperature and absolute humidity were associated with the risk of ILI, and the risk of ILI was higher in low temperature and low humidity.
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