Heat-related deaths and ambulance transports after typhoon-triggered power outages: a quasi-experimental study in the metropolitan areas of Japan

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BACKGROUND AND AIM Air conditioning use is an effective adaptation measure to prevent heat-related health problems. Any electricity supply disruptions can expose a population to non-optimal temperatures with ill effects. This study examined the mortality and morbidity impacts of sudden disruption to electricity caused by a typhoon Faxai that affected the metropolitan areas of Japan on 9th September 2019. METHODS We collected data on the daily counts of heat-related illness ambulance transport (HIAT) and all-cause deaths in 7 prefectures from July to September 2019. We used the difference-in-differences method to estimate the average treatment effect on the treated of blackout, and effect modification analysis to examine the association of heat with daily HIAT and all-cause deaths by different intensities of electricity reduction using electricity consumption data. Possible nonlinear and delayed effects of temperatures were accounted for using the distributed lag non-linear model with quasi-Poisson regression. RESULTS A total of 14,921 HIAT and 74,064 all-cause deaths were recorded during the study period. In the first three days (9th-11th September) of the blackout, the incidence rate ratio between the blackout and non-blackout areas for HIAT and all-cause deaths were 2.5 (95% confidence interval (CI): 1.8, 3.3) and 1.1 (95% CI: 1.0, 1.2), respectively. Comparing 20% reduction of electricity to no reduction, the ratio of relative risks for heat exposure (95th vs. 50th percentile temperature) was 2.3 (95% CI: 1.4, 3.8) for HIAT and 1.1 (95% CI: 0.9, 1.3) for all-cause deaths. CONCLUSIONS Typhoon-triggered reduction of electricity by 20% was associated with two times higher risk of HIAT attributable to summer heat in the metropolitan areas of Japan, while there was no evidence for all-cause deaths. Our findings suggest that emergency preparedness against blackouts in hot temperature must be activated in the face of climate change. KEYWORDS Disaster epidemiology; Blackout; Heat-related illness

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