COVID-19 pandemic as an effect modifier on the association between elevated temperatures and emergency department visits: A case-time-series study in a large population

Background: Elevated temperatures are known to be associated with increased risks for temperature-sensitive conditions. This study examines whether the coronavirus disease 2019 (COVID-19) pandemic altered the relationship between high temperatures and emergency department (ED) visits for 13 heat-sensitive conditions. Methods: We collected daily temperature, PM2.5, and ED visits data during May–September 2010–2023 in Veneto Region (4.9 million residents), Italy. We performed a case-time-series analysis using conditional quasi-Poisson and distributed lag nonlinear models. To investigate the effect modification of COVID-19, we included in the model an interaction between the cross-basis of temperature and a dummy indicator for the pre- and post-COVID-19 periods. Results: We observed 1,076,794 ED visits, 721,333 and 355,461 in the pre- and post-COVID-19 periods, respectively. Hypotension and heat illness show increased risks, especially at extreme temperatures, in both periods, with higher risk before the pandemic. This pattern is consistent across all subgroups, except for hypotension in young subjects. In contrast, respiratory diseases show a negative association in both periods, with lower relative risks post-COVID-19, particularly among women and young subjects. Dysrhythmia shows a positive association only during the post-COVID-19 period, especially in women and young people, while no significant risk appears in the pre-COVID-19 period. A similar trend is seen for diabetes in young subjects. Conclusion: These findings underscore how the pandemic has affected the association of high temperatures with ED visits for some heat-sensitive conditions. This change is not uniform across the entire population, with effects varying by specific condition and population subgroups.