Mortality risk and burden associated with non-optimum temperatures in Puerto Rico

The effects of a changing climate are already evident in Caribbean small island developing states (SIDS) like Puerto Rico, where heat episodes have become more frequent. Despite reports of increasing heat-related death rates, robust epidemiological evidence on the health impacts of high temperatures, as well as the effects of low temperatures, remains scarce, particularly outside of urban settlements in Caribbean SIDS. In this study, we conducted a case time-series study on municipality-level mortality and temperature in Puerto Rico from 2015-2023. We modeled the relationship between daily mortality count and mean temperature using a conditional quasi-Poisson regression, combined with a distributed lag non-linear model (dlnm) with a 21 d lag, adjusting for relative humidity, seasonality, and day of the week. We estimated the minimum mortality temperature (MMT)-the optimal temperature associated with the lowest mortality risk-and calculated the relative risk associated with extreme low and high temperature, defined as the 2.5th and 97.5th percentiles of daily temperature. Additionally, we estimated the municipality- and island-level excess mortality fractions attributable to both low and high temperatures, relative to MMT. Our findings indicate that exposure to non-optimum temperatures (both low and high temperatures) is significantly associated with increased mortality risk. Specifically, extreme low temperature was associated with a 1.23 (95% CI: 1.07-1.40) times risk of all-cause mortality, while extreme high temperature was associated with a 1.16 (95% CI: 1.05-1.27) times risk. We estimated that temperature-related mortality accounted for 3.88% of the total 280 568 deaths (95% eCI: 3.39%-4.29%), with low temperatures contributing 2.02% (95% eCI: 1.69%-2.32%) and high temperatures contributing 1.86% (95% eCI: 1.35%-2.35%). Furthermore, we found substantial spatial variability in temperature-related mortality burdens across municipalities. Our study identifies the vulnerable municipalities to temperature-related deaths in Puerto Rico, providing evidence to inform municipality-specific climate adaptation and mitigation strategies.