Background In recent years, regional high-temperature weather in summer occurs frequently in China. Heat stroke is the most representative meteorological disease caused by high temperature. In order to improve monitoring, early warning, prevention, and control of heat stroke, it is of great significance to understand the epidemiological characteristics of heat stroke and the associated impact of heatwave.

Objective To understand the epidemiological characteristics of heat stroke cases in Jinan City, and to explore the effects of heatwave exposure on heat stroke.

Methods Case reports of heat stroke and daily data of meteorological factors in Jinan City from 2017 to 2022 were collected. We described the temporal, population, and regional distribution characteristics of heat stroke cases in Jinan City, and used a time-stratified case-crossover design combined with conditional logistic regression model to explore the effects of heatwave exposure on heat stroke under 12 heatwave definitions (different combinations of intensity and duration). The cut-off percentiles used for heatwave definitions were the 90th (P₉₀), 95th (P₉₅), 97.5th (P_97.5), and 99th (P₉₉) percentiles of daily mean temperature; the durations were ≥ 2 d, ≥ 3 d, and ≥ 4 d, respectively. P_i(k), where i is temperature threshold, and k is duration. For example, the definition of a heatwave was notated as P₉₀(2), indicating that the daily mean temperature is ≥ P₉₀ and lasts for ≥ 2 d. Alternatively, lag01 denotes the cumulative lag effect with a 1 d lag, and so on.

Results A total of 1394 cases of heat stroke were reported in Jinan City from 2017 to 2022, including 581 mild cases and 813 severe cases, and 85 deaths were reported, with a cumulative fatality rate of 6.10%. The cases of heat stroke reported each year during the study period were concentrated from June to August and peaked in July (665 cases, 47.70%). The sex ratio of males to females in heat stroke cases was 2.02:1. A high incidence of heat stroke was in 50-89 years, with a smaller peak occurring in the age group of 50-59 years and a larger peak in the age group of 70-79 years, respectively. The high-incidence areas of heat stroke were distributed in the western part of Jinan City where city centers situated (Tianqiao District, 274 cases, 19.66%; Huaiyin District, 223 cases, 16.00%) and in the surrounding rural areas (Pingyin County, 254 cases, 18.22%). The effect of heatwave exposure on heat stroke was statistically significant during the study period. The largest effect estimates for the effect on heat stroke occurred under the heatwave definitions of P₉₉(2), P_97.5(3), and P_97.5(4) at lag04, lag03, and lag04, where corresponding OR (95%CI) values were 9.27 (4.71, 14.24), 8.95 (6.17, 12.98), and 8.22 (4.91, 13.78), respectively. The exposure-response curve showed that the risk of heat stroke tended to increase with the increase of average daily temperature.

Conclusion July is the key period for the occurrence of heat stroke among Jinan City residents, while male cases are predominant, more serious cases, age concentration in the 50-89 years. The occurrence of heatwave can further increase the risk of heat stroke with a significant lag effect.