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

Abstract

Importance: The 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. Objective: To 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. Design: We 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. Setting: A mid-sized university in the United States. Participants: University students in isolation. Main Outcomes and Measures: The 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). Results: We 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 Relevance: A 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.

Quantifying the impact of immune history and variant on SARS-CoV-2 viral kinetics and infection rebound: A retrospective cohort study

“…We found that individuals infected with SARS-CoV-2 often had Ct values <30 beyond the five-day isolation period following SARS-CoV-2 infection currently recommended by the CDC ( Centers for Disease Control and Prevention, 2022 ). This finding is in line with other studies measuring Ct values from upper respiratory tract samples, the duration of antigen test positivity, and the duration of infectious viral load or culturable virus ( Boucau et al, 2022a ; Earnest et al, 2022 ; Ke et al, 2022 ; Landon et al, 2022 ; Lefferts et al, 2022 ). While we do not have data on infectiousness by day to clarify the exact link between Ct and infectiousness, nearly half of the individuals in this cohort had potentially infectious viral loads (Ct <30) five days after their initial detection, even in those detected later in their infection course ( Singanayagam et al, 2020 ).…”

Prevalence of Positive Rapid Antigen Tests After 7-Day Isolation Following SARS-CoV-2 Infection in College Athletes During Omicron Variant Predominance

“…The use of testing before exiting isolation in the 5-to 10-day period to reduce the risk of persistent infectiousness is a common strategy used by universities, including Stanford University, and other organizations. 10,16,17 Although the present study did not evaluate the association between RAT and infectivity, previous studies have shown a good correlation between RAT and viral load. [6][7][8] One recent study found that a positive RAT on day 6 was only 50% predictive of a positive culture; however, a negative RAT on day 6 was 100% predictive of a negative culture.…”

“…These rates are similar to those previously reported for the 5-to 10-day window, ranging from 17% to 58%. 10,15,16 Individuals who tested positive on their first test were more likely to remain positive on subsequent tests with 62% of individuals testing positive on day 7 also testing positive on day 8, and 69% of those testing positive day 7 or 8 also testing positive on day 9 (Figure 1). The timing of antigen…”

Quantifying the impact of immune history and variant on SARS-CoV-2 viral kinetics and infection rebound: a retrospective cohort study

“…( 21 ) This finding is in line with other studies measuring Ct values from upper respiratory tract samples, the duration of antigen test positivity, and the duration of infectious viral load. ( 4, 22 – 24 ) While we do not have data on infectiousness by day to clarify the exact link between Ct and infectiousness, nearly half of the individuals in this cohort had potentially infectious viral loads (Ct<30) five days after their initial detection, even in those detected later in their infection course ( 25 ). By day 10, the number of individuals with Ct<30 was substantially reduced but still high.…”