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

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 PM(2.5)/CO/O(3) and HFMD risk showed moderate or substantial heterogeneity among cities ( [Formula: see text] statistics: 48.5%, 53.1%, and 61.1%). Temperature conditions significantly modified the PM(2.5)-HFMD association, while relative humidity and rainfall modified the O(3)-HFMD association. Low temperatures enhanced the protective effect of PM(2.5) exposure against HFMD risk [PM(2.5) <32.7 μg/m(3) or PM(2.5) >100 μg/m(3), at the 99th percentile: relative risk (RR) = 0.14, 95% CI: 0.03–0.60]. Low relative humidity increased the adverse effect of O(3) exposure on HFMD risk (O(3) >128.7 μg/m(3), at the 99th percentile: RR = 2.58, 95% CI: 1.48–4.50). However, high rainfall decreased the risk of HFMD due to O(3) exposure (O(3): 14.1–41.4 μg/m(3)). 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 PM(2.5) or O(3) exposure and HFMD risk.