Associations of ambient temperature and heat waves with risks of hepatitis E in Jiangsu, China (2010-2023): A time-stratified case-crossover study.

BACKGROUND

Hepatitis E virus (HEV) causes substantial morbidity globally, with frequent outbreaks in low-resource settings due to fecal-oral transmission. Temperature and extreme heat may influence waterborne pathogens, but their impact on HEV risk is unclear.

METHODS

We performed a time-stratified case-crossover study using 42,481 laboratory-confirmed hepatitis E cases reported in Jiangsu Province (2010-2023). Daily mean, maximum, and minimum temperatures were obtained from fixed-site monitoring data. We examined associations of short-term temperature (single-day and cumulative lags up to 21 days) and heat wave episodes with hepatitis E risk using conditional logistic regression. Heat waves were defined using percentile-based thresholds for consecutive days. Analyses were adjusted for relative humidity and time trends, and stratified by sex, age, residence, and occupation. Sensitivity analyses used alternative heat wave definitions and lag structures.

RESULTS

Higher ambient temperature was associated with increases in hepatitis E risk. Each 1 °C rise in daily mean temperature (lag 0-1 days) was linked to a 0.6 % higher odds of hepatitis E (OR 1.006, 95 % CI 1.002-1.010). Similar associations were observed for maximum and minimum temperatures (e.g. OR 1.005 [1.002-1.009] per 1 °C at lag 0-1 for max temperature; OR 1.009 [1.004-1.014] at lag 0-3 for min temperature). Heat waves defined by more extreme and prolonged thresholds showed stronger effects. For example, a three-day daytime heat wave above the 95th percentile (Day_HW95_3d) was associated with an 18 % higher hepatitis E risk (OR 1.18, 95 % CI 1.08-1.29), and a four-day compound heat wave >90th percentile had an OR of 1.14 (95 % CI 1.04-1.24).

CONCLUSIONS

Short-term exposure to higher ambient temperatures and heat wave events was associated with increased risk of hepatitis E in Jiangsu, China. These results suggest that climate warming and extreme heat may elevate transmission of HEV, underscoring the need for strengthened water and sanitation interventions and targeted public health planning during hot weather.