Daily Rapid Antigen Testing in a University Setting to Inform COVID-19 Isolation Duration Policy

ImportanceThe suitability of the currently recommended 5-day COVID-19 isolation period remains unclear in an Omicron-dominant landscape. Early data suggest high positivity via rapid antigen test beyond day 5, but evidence gaps remain regarding optimal isolation duration and the best use of limited RATs to exit isolation. ObjectiveTo determine the percentage of SARS-CoV-2 infected persons who remain positive via RAT on isolation day 5+ and assess possible factors associated with isolation duration. DesignWe evaluated daily rapid antigen test case series data from 324 persons in a managed isolation program who initially tested positive between January 1 and February 11, 2022, an Omicron-dominant period. Arrival tests and twice-weekly screening were mandated. Positive persons isolated and began mandatory daily self-testing on day 5 until testing negative. Trained staff proctored exit testing. SettingA mid-sized university in the United States. ParticipantsUniversity students in isolation. Main Outcomes and MeasuresThe percentage of persons remaining positive on isolation day 5 and each subsequent day. The association between possible prognostic factors and isolation duration as measured by event-time-ratios (ETR). ResultsWe found 47% twice-weekly screeners and 26-28% less frequent screeners remained positive on day 5, with the percentage approximately halving each additional day. Having a negative test [≥] 10 days before diagnosis (ETR 0.85 (95% CI 0.75-0.96)) and prior infection > 90 days (ETR 0.50 (95% CI 0.33-0.76)) were significantly associated with shorter isolation. Symptoms before or at diagnosis (ETR 1.13 (95% CI 1.02-1.25)) and receipt of 3 vaccine doses (ETR 1.20 (95% CI 1.04-1.39)) were significantly associated with prolonged isolation. However, these factors were associated with duration of isolation, not infection, and could reflect how early infections were detected. Conclusions and RelevanceA high percentage of university students during an Omicron-dominant period remained positive after the currently recommended 5-day isolation, highlighting possible onward transmission risk. Persons diagnosed early in their infections or using symptom onset as their isolation start may particularly require longer isolations. Significant factors associated with isolation duration should be further explored to determine relationships with infection duration. Key PointsO_ST_ABSQuestionC_ST_ABSWhat percentage of SARS-CoV-2 infected persons remain positive via rapid antigen test on days 5+ of isolation? FindingsIn this case series of 324 university students, 47% of twice-weekly screeners and 26-28% of less frequent screeners remained positive via rapid antigen on isolation day 5, with the percent still positive approximately halving with each subsequent day. MeaningWhile isolation duration decisions are complex, our study adds to growing evidence that a 5-day isolation may be 1-2 days too short to sufficiently reduce the onward transmission risk, particularly for those in dense settings or among vulnerable populations.