Effect of meteorological factors on the incidence of Mycoplasma pneumoniae pneumonia in Japan: a time series analysis.

Mycoplasma pneumoniae (M. pneumoniae) is a major cause of upper and lower respiratory tract infections and respiratory tract disease in humans. While accumulated pieces of epidemiological evidence suggest an association between meteorological factors and the risk of M. pneumoniae pneumonia, comprehensive nationwide studies on this topic are lacking. We aimed to systematically assess the effect of meteorological factors such as mean temperature and relative humidity on the incidence of M. pneumoniae pneumonia in Japan over a 15-year period from 2005 to 2019. The exposure - response relationships between incidence of M. pneumoniae pneumonia, mean temperature, and relative humidity in all 47 Japanese prefectures (covering whole country) for 2005 - 2019 were quantified by using a distributed lag non-linear model for each prefecture and the estimates from all the prefectures were then pooled using a multivariate mete-regression model to derive nationwide average associations. The study encompassed a total of 162,845 M. pneumoniae pneumonia cases. Our findings indicate that seasonal variations in weekly mean temperature and relative humidity were positively associated with the incidence of M. pneumoniae pneumonia. Specifically, when considering - 1.3 °C as the reference, the relative risk (RR) peaked at 16.8 °C (with RRs of 1.50, 95% confidence interval (CI): 1.32-1.70). Similarly, when using 45.5% relative humidity as the reference, the RR reached its peak at 87.7% (with RRs of 1.49, 95% CI: 1.33-1.67). These results emphasize the necessity of implementing climate change adaptation strategies and public health interventions in regions vulnerable to M. pneumoniae pneumonia.