Associations between ambient air pollution and daily incidence of pediatric hand, foot and mouth disease in Ningbo, 2014-2016: a distributed lag nonlinear model.

Hand, foot and mouth disease (HFMD) has high prevalence around the world, with serious consequences for children. Due to the long survival period of HFMD virus in ambient air, air pollutants may play a critical role in HFMD epidemics. We collected data on daily cases of HFMD among children aged 0-14 years in Ningbo City between 2014 and 2016. Distributed lag nonlinear models were used to assess the effects of particulate matter (PM2.5), sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O-3) on the daily incidence of HFMD among children, with analyses stratified by gender and age. Compared with moderate levels of air pollution, high SO2 levels had a relative risk (RR) of 2.32 (95% CI 1.42-3.79) and high NO2 levels had a RR of 2.01 (95% CI 1.22-3.31). The RR of O-3 was 2.12 (95% CI 1.47-3.05) and that of PM2.5 was 0.77 (95% CI 0.64-0.92) at moderate levels of air pollution. Specifically, high levels of SO2 and NO2 had RRs of 2.39 (95% CI 1.44-3.96) and 2.02 (95% CI 1.21-3.39), respectively, among 0-4-year-old children, while high O-3 had an RR of 2.31 (95% CI 1.09-4.89) among 5-14-year-old children. Our findings suggest significant associations of high SO2 and NO2 levels and moderate O-3 levels in HFMD epidemics, and also indicate that air pollution causes lagged effects on HFMD epidemics. Our study provides practical and useful data for targeted prevention and control of HMFD based on environmental evidence.