Risk of heat-related illnesses and preventive measures at mass gathering rock festivals in the summer of 2023 in Japan.

BACKGROUND: Mass gatherings during the peak summer months pose a notable risk for heat-related illnesses due to extreme heat and humidity. We aimed to identify trends in preventive measures taken against heat-related illnesses at mass gathering rock festivals in Japan during the summer of 2023, in terms of associations with online sources regarding the event details and heat risk communication; daily maximum wet bulb globe temperature (WBGT) values; and emergency heat-related illness transport data. METHODS: Four rock festivals (festivals A-D), held in July and August 2023, were analyzed. Publicly available online sources were reviewed to examine the event details, heat risk communication, and preventive measures. Daily maximum WBGT values were obtained from the meteorological observation points closest to each festival venue. Emergency heat-related illness transport data were assessed to identify trends during the rock festivals. RESULTS: Three festivals (festivals A, B, and D) recorded daily maximum WBGT values at or above the "Danger" threshold (≥31 °C), while festival C reached the "Severe Warning" level (≥28 °C and <31 °C). Despite the high WBGT, no heat advisories were issued on the websites of festivals A and B. Festival C gave a basic advisory on heat precautions. Festival D implemented more comprehensive countermeasures, including public warnings and recommendations to carry hats, towels, and portable fans. Notably, emergency transport for heat-related illnesses increased in the regions hosting festivals B and D. CONCLUSIONS: All festivals posed substantial heat-related health risks. Enhanced public risk communication and consistent preventive measures are essential for mitigating preventable incidents during mass gatherings in extreme heat.