Interaction Effects Between COVID-19 Outbreak and Fever on Mortality Among OHCA Patients Visiting Emergency Departments.

: Fever in patients who have suffered an out-of-hospital cardiac arrest (OHCA) has been linked to poor clinical outcomes, as a fever can exacerbate neurological damage, increase metabolic demands, and trigger inflammatory responses. This study evaluates the impact of the COVID-19 outbreak and associated fevers on OHCA outcomes and examines how they can worsen patient prognosis. : Our retrospective observational analysis used data from the National Emergency Department Information System (NEDIS), comprising adult OHCA patients at 402 EDs in Korea between 27 January and 31 December 2020 (COVID-19 pandemic period) and the corresponding period in 2019 (pre-COVID-19). The primary outcome was in-hospital mortality, with the COVID-19 outbreak as the main exposure variable and fever as an important interaction variable. We employed multilevel multivariate logistic regression with an interaction term (year of visit × fever) to examine the effects of COVID-19 and fever on mortality. Risk-adjusted mortality rates were calculated, and a difference-in-difference analysis evaluated the impact of COVID-19 on excess mortality by fever status. : During COVID-19, in-hospital mortality was higher among OHCA patients compared to the pre-pandemic period (adjusted OR 1.22, 95% CI 1.11-1.34), particularly among febrile patients (adjusted OR 1.40, 95% CI 1.24-1.59). Interaction analysis revealed that COVID-19 disproportionately increased mortality in febrile OHCA patients compared with non-febrile patients (difference-in-difference: 0.8%, 95% CI 0.2-1.5). : Our study found that the COVID-19 pandemic significantly increased mortality among OHCA patients, with febrile patients experiencing disproportionately worse outcomes due to systemic delays and pandemic-related disruptions.