Abstract
Background: The results of the association between ambient temperature and influenza in previous studies have been inconsistent in different regions. And global, multi-regional studies are lacking.
Methods: Our study used two stages of analysis to further evaluate the association between ambient temperature and influenza activity at regional and global scales. Meteorological data and influenza data were collected in 124 countries during 2014–2019. The country-specific associations between weekly mean temperature and the risk of all types of influenza (Flu-All)), influenza A (Flu-A), and influenza B (Flu-B) were estimated by using a distributed lag non-linear model (DLNM), and the pooled regional and global effects by using multilevel meta-analysis. Climate zones and influenza transmission zones performed stratified analyses.
Results: There was a non-linear curve relating ambient temperature to influenza risk in 124 countries. Within the optimal lag of 2 weeks, a bimodal (M-shaped) relationship was observed between temperature and influenza risk, with two risk peaks at -8°C with two RR of 6.02 (95% CI: 1.92-20.77) and of 3.76 (95% CI: 2.39-5.91), and at 22°C with two RR of 3.08 (95% CI: 1.27-7.49) and 2.08 (95% CI: 1.55-2.80). For Flu-B, it was N-shaped, peaking at 1°C with an RR of 4.48 (95%CI: 1.74-11.55). Risk curves fitted under geographic location-induced influenza transmission pattern zones showed a more characteristic shape than risk curves fitted under climatic zones.
Conclusions: Globally, low temperatures significantly increased the risk of influenza, and Flu-A activity dominated throughout the year with two peaks. Geographic homogeneity was relatively dominant concerning the cumulative association of influenza activity with temperature. The findings have important implications for the development of strategies to control global and regional influenza and respond to climate change.