Control of nosocomial transmission of SARS-COV-2 in the service of internal medicine in Lausanne university hospital

Introduction: Transmission of SARS-CoV-2 inside the hospital has significant implications for patients and healthcare workers. Objectives: We describe a nosocomial outbreak of SARS-CoV-2 infections in the Service of Internal Medicine, the implemented infection prevention and control (IPC) measures and their impact. Methods: We report all consecutive nosocomial cases in a 206-bed service from February 8 until April 8, 2021 (weeks 6-14). Nosocomial COVID-19 cases were defined as microbiologically documented cases by PCR, diagnosed ≥ 5 days after admission. A cluster was defined based on the detection of ≥ 2 nosocomial COVID-19 cases within a given period (< 72 h) or geographically linked. IPC measures implemented on week 10 to control SARS-CoV-2 transmissions in all non- COVID units were: systematic screening at day 3 after admission;weekly screening of all patients by PCR on saliva;and decreasing the occupancy of all patient rooms with 5 patients to 3. Results: 69 cases were identified, with 57 attributed to 21 clusters and 12 cases considered isolated. Median age was 74 years (IQR 65, 80) and 40.6% were female. All cases had a previous negative test and median time from admission to positive test was 12 days (IQR 8, 17). 45.1% of nosocomial cases were completely asymptomatic. 60.9% of patients stayed in rooms with 5-patients. Death occurred in 23.2% of cases. The incidence of nosocomial cases was the highest between weeks 8 and 10 with 18 and 17 new cases per week, respectively. After the introduction of IPC measures on week 10, there was a rapid decrease in the number of cases until complete absence of new cases on week 14. Conclusion: Nosocomial infections were frequently asymptomatic, potentially hampering fast diagnosis which is crucial for control of transmission, and were associated with high mortality rate. The implementation of additional IPC measures led to a gradual decrease in nosocomial transmissions and allowed controlling the outbreak.