Hospital-Onset and Community Delta and Omicron SARS-CoV-2 Infections

BACKGROUND: Previous studies indicated an increased risk of hospital-onset SARS-CoV-2 infections during the Delta and Omicron waves. Limitations in past research included the failure to compare hospital and general population infection rates and inadequate criteria for defining hospital-onset infections. OBJECTIVE: To assess the risk of hospital-onset SARS-CoV-2 infections during the Delta and Omicron waves, comparing rates in the hospital setting to the general population. METHODS: The study was conducted at Laniado Hospital, Israel during the Delta wave (August-September 2021) and Omicron wave (January 1-31, 2022). Patients admitted with respiratory symptoms or positive tests were isolated in a dedicated ward. Hospital-onset infections were identified as patients testing negative upon admission but positive during their stay. Rates were compared with community infection rates and those reported in other centers. RESULTS: Hospital-onset infections were higher during the Omicron wave but were consistently lower than expected based on general population data. Relative to the general population, in-hospital onset infections were below 50% during the Delta wave and below 15% during the Omicron wave. The rate was lower than that reported elsewhere that used methods that didn't include patient segregation. CONCLUSIONS: Despite not universally using high-filtration masks or conducting repeated PCR testing, hospital-acquired infections were minimized by segregating patients in dedicated wards. The study suggests patient segregation in specialized wards is the most effective component in preventing in-hospital transmission.