Healthcare-associated COVID-19 infections and mortality

Background: It is crucial to quantify the impact of healthcare-associated COVID-19 infections (HAIs) and the resulting mortality to evaluate the requirement for implementing infection prevention and control (IPC) strategies within the healthcare setting. Aim: To investigate the occurrence of HAIs and associated mortality among hospitalized patients in Norway. Methods: A retrospective registry-based study was conducted using national health data in Norway. The study included patients hospitalized between January 1st, 2019, and January 1st, 2023, comparing those with HAI and community-associated COVID-19 infections (CAIs). In all, 54,885 COVID-19 cases were identified, of which 1188 cases met our HAI definition. A total of 742 hospitalized patients with HAI were matched to 2583 hospitalized patients diagnosed with COVID-19 at a later stage by age, sex, length of stay, and hospital unit. HAI was defined as a registered positive SARS-CoV-2 test at least seven days after hospitalization, but before hospital discharge. The primary outcome was 365-day mortality, categorized by HAI or CAI status, quantified by Cox regression and adjusted for age, sex, and diagnoses. Secondary outcomes included mortality variations based on vaccination status and causes of death. Findings: Mortality rates were consistently higher among HAI patients compared to CAI patients, the difference being highest shortly after infection. Vaccination significantly reduced all-cause and COVID-19 mortality risk. Conclusion: HAI consistently led to higher mortality than CAI, especially during the Omicron phase. Vaccination effectively reduced mortality across both groups. These findings emphasize the importance of IPC measures and vaccination in mitigating the impact of HAIs.