Short‐Term Effects of Temperature and Relative Humidity on Hand, Foot, and Mouth Disease in Guiyang, China, From 2022 to 2024: Distributed Lag Nonlinear Model–Based Analysis

ABSTRACT Background Meteorological factors, including temperature and relative humidity, have been associated with the incidence of hand, foot, and mouth disease (HFMD). However, these associations vary across regions. Guiyang, a city characterized by a subtropical plateau humid climate, remains understudied with respect to the short‐term associations of temperature and relative humidity with HFMD incidence. This study aimed to quantify the short‐term associations of these meteorological factors with HFMD risk in this understudied setting. Methods Daily HFMD surveillance and meteorological data (temperature and relative humidity) from Guiyang, China (2022–2024) were analyzed using a distributed lag nonlinear model to characterize exposure–lag–response associations over a maximum lag of 14 days. Relative risks (RRs) with 95% confidence intervals (CIs) were estimated to quantify the effects. Subgroup analyses by sex, age group, and the population category were also performed to identify susceptible populations. Results A total of 42,910 HFMD cases among children aged 0–14 years were included. Both temperature and relative humidity exhibited nonlinear associations with HFMD risk. For temperature, risk peaked at 27.00°C with a 3‐day lag (RR = 1.10; 95% CI: 1.06–1.15). For relative humidity, the highest point estimate of risk occurred at 94% relative humidity on the exposure day (RR = 1.10; 95% CI: 0.92–1.34). The high‐temperature–high‐relative‐humidity condition was associated with the highest cumulative risk (RR = 1.30; 95% CI: 1.04–1.64). The condition involving extremely low temperature and relative humidity was associated with persistent protective effects. Subgroup analyses revealed that children younger than 3 years and scattered children were more susceptible to the effects of the high‐temperature–high‐relative‐humidity condition. Conclusions Temperature and relative humidity were associated with HFMD incidence in Guiyang, with nonlinear and lagged associations observed, and the highest cumulative risks were observed under the high‐temperature–high‐relative‐humidity condition. These findings support the consideration of meteorological factors in HFMD early warning systems and suggest the need for targeted interventions during high‐risk weather conditions.