Unraveling meteorologically influenced recurrence and sequential infection risks among influenza, mumps, scarlet fever, and hand-foot-and-mouth disease: evidence from Shenzhen, China.

BACKGROUND: Meteorological factors are key triggers for infectious diseases in high-density cities, yet their influence on the acute disease patterns of influenza, mumps, scarlet fever, and hand-foot-and-mouth disease (HFMD) remains unclear. This study aims to reveal the variations in relative risk and secondary infection associated with meteorological factors, thereby providing clues for further confirmatory research. METHODS: We analyzed city-wide incidence data from 2012 to 2020 alongside daily meteorological observations. Distributed lag non-linear models (DLNM) were used to quantify exposure-lag-response relationships. Andersen-Gill models assessed effects on disease recurrence, and Cox models evaluated risks of sequential infections between disease pairs, stratified by season. RESULTS: The peak-risk temperatures were 14.5 °C for influenza, 18.5 °C for mumps, 17 °C for scarlet fever, and 28.5 °C for hand-foot-and-mouth disease (HFMD). Average temperature (AT) increase raised influenza recurrence risk (e.g., 1.3% higher risk per 1 °C in children aged 0-14 years). Greater temperature variability reduced sequential infection risk for influenza after HFMD in the cold season (Hazard Ratio [HR] = 0.16) and warm season (HR = 0.14). Increased diurnal temperature range also lowered this risk in the cold season (HR = 0.09). Higher AT in warm season reduced sequential infection risks from influenza to HFMD (HR = 0.61). Increased relative humidity was protective in the cold season but became a risk factor in the warm season in specific disease. CONCLUSION: Meteorological factors are pivotal in modulating the dynamics of common infections, and influencing both recurrence and sequential transmission. The protective effect of increased temperature variability against secondary infections highlights a complex climate-susceptibility interaction at the population level.