Background Heat stroke is a severe heat-related illness, and it is necessary to explain in depth the effect of high temperature on heat stroke in the context of global warming.

Objective To describe the epidemiological characteristics of reported heat stroke cases in Shanghai from 2013 to 2022, analyze the influence of daily mean temperature threshold on heat stroke, and identify susceptible populations, so as to provide data support for the development of relevant social and public policies.

Methods Data from case reports on heat stroke were collected in Shanghai from 2013 to 2022. Heat stroke associated daily mean temperature threshold, lag effects, and susceptible populations were estimated using piecewise regression model and distributed lag non-linear model.

Results Among the 3479 cases reported from June to August of 2013—2022 in Shanghai, the male-to-female ratio was 3.34. A positive association between daily mean temperature and heat stroke was found, the association was strongest on the day of exposure and persisted until lag day 2, with an estimated threshold at 33.1 ℃. Using the median value of daily mean temperature as the reference value (28.1 ℃), the peak cumulative effect of extreme high temperature (33.1 ℃) appeared at lag 0-2 days with a relative risk (RR) value and its 95%CI of 25.32 (17.49-36.64) for all included cases; the RRs for male and female were 26.33 (17.78, 38.98) and 25.20 (12.52, 50.72), respectively, and no statistically significant difference was found between sexes (P＞0.05); the RRs were much greater in population aged 45-64 years (25.17, 95%CI: 15.54, 40.78) and 65 years and above (76.98, 95%CI: 34.80, 170.30), significantly higher than the values in those aged 16-44 years (20.22, 95%CI: 12.22, 33.44) (P＜0.05); urban areas showed a greater RR (49.09, 95%CI: 19.60, 122.95) than rural areas (23.65, 95%CI: 16.13, 34.67) (P＜0.05).

Conclusion High temperature is significantly associated with heat stroke cases reported in Shanghai, with a threshold of 33.1℃ for daily mean temperature. The middle-aged and elderly adults and urban residents are more vulnerable to heat stress than those younger and living in rural areas.