Interactive and joint effects of multiple meteorological and air pollution exposures on hand, foot and mouth disease risk in western China: a time-series analysis

Introduction Hand, foot and mouth disease (HFMD) is influenced by meteorological and air pollution factors. However, few studies have evaluated their joint and interactive effects under real-world multi-exposure conditions. This study examined the health impacts of environmental mixtures and identified susceptible populations in western China.Methods A total of 484 928 HFMD cases in children under 6 years old were collected from western China. Bayesian kernel machine regression was used to estimate the effects of simultaneous exposure to temperature, precipitation, shortwave radiation, pressure, fine particulate matter (PM2.5) and ozone (O3). Subgroup analyses were conducted by age, sex and region type.Results Temperature, precipitation, shortwave radiation, PM2.5 and O3 were associated with HFMD risk. Notable non-linear interactions were detected between temperature, shortwave radiation or O3 and other exposures. For instance, under median temperature conditions, increasing shortwave radiation was associated with a higher HFMD risk, with relative risks (RRs) of 1.20 (95% credible interval (95% CrI) 0.95 to 1.51), 1.91 (1.54 to 2.37) and 3.16 (2.05 to 4.87) at the 25th, 50th and 75th percentiles, respectively. In contrast, O₃ appeared to attenuate the risk, with RRs decreasing from 4.19 (3.06 to 5.73) at the 25th percentile to 1.33 (1.03 to 1.72) at the 75th. Joint exposure analysis further revealed a protective association under low combined exposure levels, with the RR of 0.46 and an elevated risk under high exposure levels, with an RR of 1.62. Subgroup analyses indicated higher susceptibility among boys, children aged 0–2 years and residents of ethnic minority-concentrated regions.Conclusion This study enhanced understanding of the joint and interactive effects of meteorological and air pollution factors on HFMD risk under real-world conditions and identified vulnerable subgroups, supporting future research and targeted prevention efforts.