Aurelio Tobias, Yasushi Honda, Lina Madaniyazi, Barrak Alahmad, Erik Lavigne, Dominic Royé, Shilu Tong, Micheline de Sousa Zanotti Stagliorio Coelho, Veronika Huber, Ales Urban, Susana das Neves Pereira da Silva, Souzana Achilleos, Robbie M. Parks, Carmen Íñiguez, Pierre Masselot, Ana M. Vicedo-Cabrera, Ben Armstrong, Antonio Gasparrini, Masahiro Hashizume, Rosana Abrutzky, Souzana Achilleos, Fiorella Acquaotta, Barrak Alahmad, Ben Armstrong, Hanne Krage-Carlsen, Gabriel Carrasco, Paul Lester Carlos Chua, Micheline de Sousa Zanotti Stagliorio Coelho, Valentina Colistro, Susana das Neves Pereira da Silva, Francesca d e'Donato, Bertil Forsberg, Antonio Gasparrini, Yue Leon Guo, Yuming Guo, Iván Gutiérrez-Ávila, Masahiro Hashizume, Iulian-Horia Holobaca, Yasushi Honda, Veronika Huber, Magali Hurtado Diaz, Carmen Íñiguez, Haidong Kan, Ho Kim, Yoonhee Kim, Wissanupong Kliengchuay, Jan Kyselý, Eric Lavigne, Whanhee Lee, Yuanyu Lu, Lina Madaniyazi, Joana Madureira, Pierre Masselot, Patricia Matus Correa, Paola Michelozzi, Chris Fook Sheng Ng, Samuel Osorio, Ala Overcenco, Shih‐Chun Pan, Robin Park, Robbie M. Parks, Mathilde Pascal, Martina S. Ragettl, Dominic Royé, Paulo Hilario Nascimento Saldiva, Alexandra Schneider, Joel Schwartz, Noah Scovronick, Xerxes Seposo, Francesco Sera, Muhammad Abdul Basit Ahmad Tajudin, Kraichat Tantrakarnapa, Aurelio Tobias, Shilu Tong, Ales Urban, Nicolás Valdés Ortega, Ana M. Vicedo-Cabrera, Antonella Zanobetti
BACKGROUND: Heatstroke represents the most severe manifestation of heat exposure. Heatstroke is rare and under-reported, resulting in limited empirical data on its global incidence and burden. This study aimed to examine geographical variations and temporal trends in reported heatstroke mortality across multiple countries. METHODS: We collected annual heatstroke mortality data from 34 countries participating in the Multi-Country Multi-City Collaborative Research Network between 2000 and 2022, using the ICD-10 code X30. Country-specific mortality rates were estimated using Poisson regression, alongside analyses of annual trends and associations with mean warm-season temperature. We also assessed the proportion of heatstroke deaths relative to both overall heat and extreme heat-attributable all-cause mortality. FINDINGS: Heatstroke mortality rates varied widely across countries, with Japan reporting the highest rate (5·81 per 1 million population; 95% CI 4·43-7·62), followed by Cyprus (2·51; 1·36-4·61), and China (2·42; 1·21-4·85). By contrast, most countries in Europe, South America, and southeast Asia reported rates of less than one death per 1 million population. Heatstroke mortality increased over time in several countries and was associated with warm-season temperatures in most regions. The proportion of heatstroke deaths relative to overall heat-attributable mortality ranged from less than 1% in many countries to as close to 24% in Japan. When analyses were restricted to deaths attributable to extreme heat, the proportion of heatstroke deaths increased substantially. INTERPRETATION: Our broad international assessment of heatstroke mortality highlights its distinct patterns compared with overall heat-attributable mortality. The observed variability likely reflects differences in recognition, reporting, and diagnostic practices, while climate exposure and health system capacity influence whether heat-related deaths are identified and recorded as heatstroke. FUNDING: The Japan Society for the Promotion of Science and the Environment Research and Technology Development Fund of the Environmental Restoration and Conservation Agency provided by the Japanese Ministry of the Environment.