Background In the context of global warming, extreme weather events occur frequently across the world, and their influences on the incidences of hand-foot-mouth disease (HFMD) raise concerns.

Objective This study evaluates the effects of extreme meteorological factors on the risk of HFMD in children aged 0-6 years in Xiaoshan District of Hangzhou, and provides scientific evidence for the prevention and control of the disease.

Methods The HFMD cases aged 0-6 years in Xiaoshan District of Hangzhou from 2009 to 2019 were retrieved from the information system of the Chinese Center for Disease Control and Prevention and the follow-up records, and meteorological variables of the same period were sourced from the China Meteorological Data Service Center. The influences of extreme meteorological factors (versus P₅₀) over certain lag time on HFMD incidence were analyzed by a distributed lag nonlinear model (DLNM) adjusting for potential confounders such as secular trend, day of the week, and holidays. All effects were presented as relative risks (RR) for the 90th or 10th percentiles of the meteorological variables using their P₅₀ values as reference. Stratified analysis was performed by gender, age (0-3 and 4-6 years), child-rearing method (sporadic children and institutional preschool children), and residence (village and community).

Results From 2009 to 2019, a total of 21 965 HFMD cases aged 0-6 years were reported in Xiaoshan District of Hangzhou, and the peak incidence was from May to July. The boy-to-girl ratio was 1.14:1. Children of 0-3 years old and of 4-6 years old accounted for 65.86% (14 467 cases) and 34.14% (7 498 cases) of the total cases respectively. There were 76.45% sporadic children and 23.55% institutional preschool children, and 68.12% village children and 31.88% community children. Selected meteorological factors had nonlinear and lagged impacts on the incidence of HFMD. The risk of HFMD of extreme heat (P₉₀, 29.4℃) was the highest (RR=1.54, 95% CI:1.34-1.77) on the current day, and such risk still existed at lag 3-8 days when reference temperature was 18.9℃. Both extreme humidity (P₉₀, 91%) at lag 5 days and extreme precipitation (P₉₀, 14.5 mm) at lag 6 days increased 5% risks of reporting HFMD when relative humidity of 73% and no rainfall were taken as reference respectively. No sunshine exposure (P₁₀) had effects at lag 4-11 days and had the highest effect at lag 5 days (RR=1.04, 95% CI:1.02-1.07) when taking sunshine duration of 4.1 h as reference. The stratified analysis results showed that both extreme heat and extreme humidity had a close harmful effect on all subgroups. Boys, children aged 4-6 years, and children in villages were more vulnerable to the effects of extreme precipitation than girls, children under 3 years, and children in communities, respectively. Children less than 3 years old were more vulnerable to the effects of no sunshine exposure than children of 4-6 years old.

Conclusion Extreme heat, humidity, and precipitation and no sunshine exposure would increase the risk of reporting HFMD among children.