Surveillance epidemiology of heatstroke in China: when numerators are denominators

In the age of big data, surveillance systems capture vast amounts of information, but the bottleneck lies in interpretation for timely public health action. Heatstroke is a textbook example of surveillance epidemiology of a climate-sensitive illness. A recent analysis based on China CDC's Heatstroke Cases Reporting System reported 86,406 heat-related illness cases from 2010 to 2023.1 From this single case pool, public health professionals derived several key metrics: incidence density and case-fatality rate (CFR).