Nationwide analysis of cases of emergency transport due to heatstroke in Japan from 2010 to 2024.

Heatstroke has become an increasingly urgent public health concern in Japan, particularly among older adults, as global warming leads to more frequent and intense heatwaves. This study analyzed national trends in heatstroke-related emergency transports from 2010 to 2024 using Fire and Disaster Management Agency surveillance data in Japan, focusing on age distribution, case severity, place of occurrence, and regional variation. Heatstroke transports increased over the study period with clear seasonal peaks in July and August. Older adults (≥ 65 years) consistently represented the largest affected group, accounting for an average of 50.7% of all cases. Despite Japan's widespread use of air conditioning, indoor settings accounted for 39.9% of incidents, most commonly at home. While deaths confirmed at the first examination were rare (< 0.3%), 35.4% of transported patients required hospitalization for moderate or severe heatstroke, including 2.4% classified as severe. In recent years, heatstroke incidence has increased notably in northern Japan, a region historically considered at lower risk, coinciding with particularly high annual temperature deviations in some northern areas. These findings indicate that preventing emergency transports in Japan will require targeted protection of older adults and the strengthening of region-specific preparedness in cooler areas where acclimatization and risk perception may be lower.