Modeling effectiveness of testing strategies to prevent COVID-19 in nursing homes -United States, 2020.

Background SARS-CoV-2 outbreaks in nursing homes can be large with high case fatality. Identifying asymptomatic individuals early through serial is recommended to control COVID-19 in nursing homes, both in response to an outbreak (outbreak testing of residents and healthcare personnel) and in facilities without outbreaks (non-outbreak testing of healthcare personnel). The effectiveness of outbreak and isolation with or without non-outbreak was evaluated. Methods Using published SARS-CoV-2 transmission parameters, the fraction of SARS-CoV-2 transmissions prevented through serial (weekly, every three days, or daily) and isolation of asymptomatic persons compared to symptom-based and isolation was evaluated through mathematical modeling using a Reed-Frost model to estimate the percentage of cases prevented (i.e., effectiveness) through either outbreak alone or outbreak plus non-outbreak testing. The potential effect of simultaneous decreases (by 10%) in the effectiveness of isolating infected individuals when instituting strategies was also evaluated. Results Modeling suggests that outbreak could prevent 54% (weekly with 48-hour test turnaround) to 92% (daily with immediate results and 50% relative sensitivity) of SARS-CoV-2 infections. Adding non-outbreak could prevent up to an additional 8% of SARS-CoV-2 infections (depending on test frequency and turnaround time). However, added benefits of non-outbreak were mostly negated if accompanied by decreases in infection control practice. Conclusions When combined with high-quality infection control practices, outbreak could be an effective approach to preventing COVID-19 in nursing homes, particularly if optimized through increased test frequency and use of tests with rapid turnaround.