[Effect of temperature on the incidence of hepatitis A in Liaoning Province: a case-crossover study]

Objective: To explore the impact of temperature on the incidence of hepatitis A and assess the incidence risk. Methods: We collected data on hepatitis A cases and meteorological factors in Liaoning, China, from January 2014 to December 2023. The time-stratified case-crossover design, a distributed lag nonlinear model, and the conditional logistic regression model were used to explore the exposure-response relationship between daily average temperature and the incidence of hepatitis A, and to calculate the excess incidence risk associated with temperature changes. Results: Between 2014 and 2023, 14 394 hepatitis A cases were reported in Liaoning, primarily in Dandong, Dalian, and Shenyang (71.86%). The median exposed temperature was 6.76 ℃. Temperature had a lag effect on the incidence of hepatitis A, with the maximum lag period reaching 28 days. The effect sizes were the greatest at a lag of 15 days under extremely low temperature and high temperature conditions (for low temperature, the peak OR=1.14, 95%CI: 1.09-1.19; for high temperature, OR=1.02, 95%CI: 1.01-1.04). The incidence risk increased with the decrease in temperature. For every 1.00 ℃ decrease in temperature, the excess incidence risk of hepatitis A was 5.64% (95%CI: 4.62%-6.64%). Subgroup analysis revealed that the excess incidence risk was higher in males (6.27%) than in females (4.66%), and higher in the cold season (6.87%) than in the warm season (4.43%). Gender and season have an effect modification. The excess incidence risks were 4.87% for those <30 years old and 5.94% for those 30-59 years old. In Dandong and Dalian, the rates were 9.26% and 7.34% respectively (all P<0.05). For individuals aged ≥60 years old (3.75%), in Shenyang (2.46%), and in other cities (1.24%), the impact of temperature on hepatitis A incidence was not statistically significant (all P>0.05). Conclusions: In Liaoning, the exposure-response relationship between temperature and the incidence of hepatitis A indicates that the incidence risk increases with decreasing temperature. The risks are particularly prominent during the cold season, affecting males and young populations, as well as in the regions of Dandong and Dalian. It is recommended to strengthen the monitoring and early warning of hepatitis A incidence by integrating meteorological data.