Mass rapid diagnostic testing as a public health response to SARS-COV-2 outbreaks in long-term care settings

Introduction: Antigen rapid diagnostic testing (Ag-RDT) is more affordable and less logistically demanding than RT-PCR for SARSCoV- 2 surveillance, but less diagnostically sensitive. This trade-off has fuelled debate about whether Ag-RDT convenience outweighs elevated risk of false negative diagnoses. Objectives: To evaluate the public health performance of reactive population screening using Ag-RDT in response to emerging nosocomial SARS-CoV-2 outbreaks. Methods: We simulated SARS-CoV-2 outbreaks across a range of long-term care facilities (LTCFs) with different Covid-19 interventions in place (social distancing, face masks, vaccination). Assuming that individuals with true positive test results were isolated and no longer transmitted, we evaluated performance of routine RT-PCR testing (tests for all individuals with Covid-19 symptoms and all new hospital admissions) and reactive mass screening using Ag-RDT (population-wide testing upon outbreak detection). Imperfect and time-varying diagnostic sensitivity was accounted for. We reported efficacy as the proportion of nosocomial infections averted in the two weeks following outbreak detection, and efficiency as the number of nosocomial infections averted per 1,000 tests used. Results: Across LTCFs, routine RT-PCR testing prevented a mean 40-47% of nosocomial infections. With the addition of a single round of reactive Ag-RDT screening, 58-63% of infections were averted. This increased to up to 69-75% when conducting a further second round of screening, with greatest performance 4-5 days after the first round. In addition to routine RT-PCR, a single round of well-timed Ag-RDT screening prevented a mean 15.2 infections/1000 Ag-RDT tests in a high-risk LTCF, but in a low-risk LTCF just 0.5 infections/1000 test. Conclusion: For LTCFs alerted to potential SARS-CoV-2 outbreaks, reactive mass Ag-RDT screening is an effective means to detect asymptomatic and pre-symptomatic infections and limit subsequent nosocomial transmission. A well-timed second round of follow-up screening can help overcome limited and time-varying nature of Ag-RDT sensitivity. Health-economic gains of Ag-RDT screening scale with outbreak risk. (Figure Presented).