Estimating transmission pathways of COVID-19 in U.S. nursing homes

BackgroundPathogen transmission dynamics in nursing homes are unique due to the interactions between staff and residents. Understanding the differences in transmission rates between and among staff and residents can identify the transmission pathways that contributed most to the spread of SARS-CoV-2 in U.S. nursing homes during the pandemic. MethodsWe used publicly available U.S. National Healthcare Safety Network (NHSN) surveillance data on resident and staff cases, vaccination, and resident deaths during June 2020-June 2022, to estimate SARS-CoV-2 transmission between and among residents and staff. We used a Bayesian inversion transmission model to produce the estimates. We categorized nursing homes by the number of beds, average length of stay, or community social vulnerability. We estimated weekly transmission events for three periods: pre-Delta (June 2020--March 2021), Delta (April 2021--October 2021), and Omicron (November 2021--June 2022). ResultsWeekly transmission events within each nursing homes category were highest between residents in homes with >299 beds during Omicron (0.66, 95% Credible Interval (CrI): 0.13-0.93), from staff to residents in homes with average length of stay >10 weeks during pre-Delta (0.88, 95% CrI: 0.06-1.85), and between residents in homes in communities with the lowest social vulnerability index during pre-Delta (0.89, 95% CrI: 0.07-1.16). ConclusionsTransmission from staff to residents and between residents may have contributed more to SARS-CoV-2 spread in nursing homes than resident-to-staff and staff-to-staff transmission. Interventions interrupting these transmission pathways and that consider community exposures could reduce the size or duration of future outbreaks.