Predicting Ambulance Transport for Heat-Related Illness in Working Populations Under Climate Change and Evaluating...

Since June 2025, Japan has mandated countermeasures to prevent outdoor laborers from developing heat-related illness at work. However, the extent to which preventive behaviors can reduce the actual heatstroke risk has not been quantified. The present study aimed to (i) project future trends in the daily number of heat-related ambulance transports in the working population under climate change, and (ii) evaluate the population-level preventive impact of workplace-adopted preventive behaviors using effect estimates from observational data.

Using daily maximum wet-bulb globe temperature, a long-term future projection of heat-related ambulance transports was performed in the working population. A cross-sectional survey was carried out to infer the effect size of behavioral interventions. The effectiveness of taking preventive behaviors was evaluated by increasing the coverage rate of workers adhering to all four behaviors (current: 23%): (i) regular hydration, (ii) use of an air-cooling vest, (iii) checking their own health condition before work, and (iv) recognizing warning signs. Theoretical scenarios in which workplace instructions to workers or teams increased adherence by 50%, 100%, and 300% relative to baseline were considered, corresponding to coverage rates at 34%, 45%, and 91%, respectively, and we evaluated the associated reduction in heatstroke risk.

Many future years were projected to have higher annual levels of heat-related ambulance transports than the median value from 2018-2024, indicating a long-term increasing trend. Even when all four possible countermeasures were implemented at an additional 50%, 100% or 300% from the current rate, the expected relative risk reduction in transports was 3.2%, 6.3%, and 19.0%, respectively, indicating only a small effect on future projected heat-related illnesses.

The number of heat-related ambulance transports is expected to increase; however, the relative risk reduction with behavioral intervention is likely limited. A fundamental overhaul of working regulations and environment (e.g., drastic shift in working hours to earlier morning) is required via adaptation policies, and mitigation of climate change is vital.