Too hot and too humid in the Caribbean: Impacts of extreme heat events and non-accidental mortality in the tropical island of Puerto Rico (2015-2020)

Background: The complex interactions between heat and public health in tropical environments are not well understood, limiting the integrated understanding of heat-related impacts on the sustainability and resilience of the affected populations. Objectives: To provide evidence on the impact of heat stress on mortality in Puerto Rico by means of indices that are based on physiologically relevant environmental factors. Methods: Daily data on non-accidental mortality for the period of 2015-2020 were obtained from the Puerto Rico Department of Health. We obtained 2 meter ambient air temperature data across the whole geographical extent of Puerto Rico and for the 2015-2020 period at an hourly step from the ERA5 climate reanalysis dataset. We employed two indices derived from thermo-physiological models: the Universal Thermal Climate Index (UTCI) and the Heat Index (HI). Poisson regression models were fitted to explain the total number of deaths as a function of UTCI and HI while adjusting for sex and age. Results: We observed an increase in overall non-accidental mortality in the days categorized as the highest tertile of both HI (IRR: 1.23, 95% CI: 1.21; 1.25) and UTCI (IRR:1.47, 95% CI: 1.44; 1.49) in the adjusted model. Myocardial infarction, ischemic heart disease, heart failure, and cerebrovascular disease were some of the primary causes of death. Conclusion: Results will provide local decision-makers with sufficient evidence on heat stress impacts and valuable information on vulnerability that can be translated into heat adaptation strategies in Puerto Rico.