City-level meteorological conditions modify the relationships between exposure to multiple air pollutants and the risk of pediatric hand, foot, and mouth disease in the Sichuan Basin, China.

ABSTRACT

Background: Several studies have examined the effects of city-level meteorological conditions on the associations between meteorological factors and hand, foot, and mouth disease (HFMD) risk. However, evidence that city-level meteorological conditions modify air pollutant-HFMD associations is lacking. Methods: For each of the 17 cities in the Sichuan Basin, we obtained estimates of the relationship between exposures to multiple air pollutants and childhood HFMD risk by using a unified distributed lag nonlinear model (DLNM). Multivariate meta-regression models were used to identify the effects of city-level meteorological conditions as effect modifiers. Finally, we conducted subgroup analyses of age and sex to explore whether the modification effects varied in different subgroups. Results: The associations between PM2.5/CO/O3 and HFMD risk showed moderate or substantial heterogeneity among cities (I2 statistics 48.5%, 53.1%, and 61.1%). Temperature conditions significantly modified the PM2.5-HFMD association, while relative humidity and rainfall modified the O3-HFMD association. Low temperatures enhanced the protective effect of PM2.5 exposure against HFMD risk [PM2.5 <32.7 µg/m3 or PM2.5 >100 µg/m3, at the 99th percentile relative risk (RR) = 0.14, 95% CI 0.03-0.60]. Low relative humidity increased the adverse effect of O3 exposure on HFMD risk (O3 >128.7 µg/m3, at the 99th percentile RR = 2.58, 95% CI 1.48-4.50). However, high rainfall decreased the risk of HFMD due to O3 exposure (O3 14.1-41.4 µg/m3). In addition, the modification effects of temperature and relative humidity differed in the female and 3-5 years-old subgroups. Conclusion: Our findings revealed moderate or substantial heterogeneity in multiple air pollutant-HFMD relationships. Temperature, relative humidity, and rainfall modified the relationships between PM2.5 or O3 exposure and HFMD risk.