Antigen Test Positivity After COVID-19 Isolation — Yukon-Kuskokwim Delta Region, Alaska, January–February 2022

Lefferts, Brian; Blake, I. G.; Bruden, Dana; Hagen, Melissa B.; Hodges, Ellen; Kirking, Hannah L.; Bates, Elizabeth E. M.; Hoeldt, Amanda; Lamont, Brenda; Saydah, Sharon; MacNeil, Adam; Bruce, Michael G.; Plumb, Ian D.

doi:10.15585/mmwr.mm7108a3

Cited by 39 publications

(54 citation statements)

References 8 publications

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“…In this study of mostly young, vaccinated individuals with mild COVID-19 and presumed Omicron variant, we found that most (75%) remain positive by rapid antigen testing on day 6, and a third through day 10. This is consistent with two recent cross-sectional studies in health care workers 15 and in a community cohort of mixed-vaccinated individuals 16 . Similar to Lefferts et al, we saw a trend to earlier negative RAT in individuals asymptomatic at diagnosis that did not reach significance in this smaller, fully vaccinated cohort.…”

Section: Discussionsupporting

confidence: 92%

“…Specifically, two recent cross-sectional studies reported 43% and 54% RAT positivity in health care workers and in the community, respectively, after day 5. These results imply that the use of rapid antigen testing would significantly lengthen isolation periods for many people 15,16 . However, we lack systematic data in the Omicron era on the relationship between RATs and viral culture, and thus RATs and infectiousness after day 5, as they were not developed and approved for this use.…”

Section: Introductionmentioning

confidence: 98%

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Evaluation of the role of home rapid antigen testing to determine isolation period after infection with SARS-CoV-2

Cosimi

Kelly

Esposito

et al. 2022

Preprint

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ImportanceRecent CDC COVID-19 isolation guidance for non-immunocompromised individuals with asymptomatic or mild infection allows ending isolation after 5 days if asymptomatic or afebrile with improving symptoms. The role of rapid antigen testing in further characterizing the risk of viral transmission to others is unclear.ObjectiveUnderstand rates of rapid antigen test (RAT) positivity after day 5 from a positive COVID-19 test and the relationship of this result to symptoms and viral culture.DesignIn this single center, observational cohort study, ambulatory individuals newly testing SARS-CoV-2 positive completed daily symptom logs, and RAT self-testing starting day 6 until negative. Anterior nasal and oral swabs were collected on a subset for viral culture.Main Outcomes and MeasuresDay 6 SARS-CoV-2 RAT result, symptoms and viral culture.Results40 individuals enrolled between January 5 and February 11, 2022 with a mean age of 32 years (range 22 to 57). 23 (58%) were women and 17 (42%) men. All were vaccinated. 33 (83%) were symptomatic. Ten (25%) tested RAT negative on day 6. 61 of 90 (68%) RATs performed on asymptomatic individuals after day 5 were positive. Day 6 viral cultures were positive in 6 (35%) of 17 individuals. A negative RAT or being asymptomatic on day 6 were 100% and 78% predictive respectively for negative culture, while improving symptoms was 69% predictive. A positive RAT was 50% predictive of positive culture.Conclusion and RelevanceRATs are suboptimal in predicting viral culture results on day 6. Use of routine RATs to guide end of COVID-19 isolation could result in significant numbers of culture negative, potentially non-infectious individuals undergoing prolonged isolation. However, a negative RAT was highly predictive of being culture negative. Complete absence of symptoms was inferior to a negative RAT in predicting a negative culture result, but performed better than improving symptoms. If a positive viral culture is a proxy for infectiousness, these data may help further refine a safer strategy for ending isolation.

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Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 98%

Evaluation of the role of home rapid antigen testing to determine isolation period after infection with SARS-CoV-2

Cosimi

Kelly

Esposito

et al. 2022

Preprint

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“…Studies of managed isolation programs reported RAT positivity ranging from 31-58% on days 5-9 of isolation and PCR positivity ranging from 39-52% on day 5, 25-33% on day 6, and 13-22% on day 7. 3,[5][6][7] Our results indicate that a 7-day isolation period is required to achieve at least a 90% probability of being negative without exit testing (Figure 1A-C). 5-day and 6-day isolation periods are associated, respectively, with a 53-74% and 78-85% probability of testing negative (range across last negative test categories).…”

Section: Discussionmentioning

confidence: 83%

“…Studies of managed isolation programs through schools or employers found positivity via rapid antigen test (RAT) on days 5-9 ranging from 31-58%, although daily testing among all persons was not conducted. [5][6][7] A near-daily PCR testing study reported a day 5 positivity of ranging from 39-52%. 3 However, key gaps in our understanding persist.…”

Section: Introductionmentioning

confidence: 99%

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

Earnest

Chen

Chaguza

et al. 2022

Preprint

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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.

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“…19 Our findings are similar to early reports in other settings suggesting 30-55% positive antigen RDT between days 5-10 of illness. 20,21,7 One study, using a different antigen test, showed higher antigen RDT positivity (75%), but similar culture positivity (35%) at day 6. 20 Given the similar negative predictive value, the work by Cosimi et al 22 highlights possible differing performance characteristics at the end of infection across tests.…”

Section: Discussionmentioning

confidence: 99%

Viral dynamics of Omicron and Delta SARS-CoV-2 variants with implications for timing of release from isolation: a longitudinal cohort study

Bouton

Atarere

Turcinovic

et al. 2022

Preprint

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BackgroundIn January 2022, United States guidelines shifted to recommend isolation for 5 days from symptom onset, followed by 5 days of mask wearing. However, viral dynamics and variant and vaccination impact on culture conversion are largely unknown.MethodsWe conducted a longitudinal study on a university campus, collecting daily anterior nasal swabs for at least 10 days for RT-PCR and culture, with antigen rapid diagnostic testing (RDT) on a subset. We compared culture positivity beyond day 5, time to culture conversion, and cycle threshold trend when calculated from diagnostic test, from symptom onset, by SARS-CoV-2 variant, and by vaccination status. We evaluated sensitivity and specificity of RDT on days 4-6 compared to culture.ResultsAmong 92 SARS-CoV-2 RT-PCR positive participants, all completed the initial vaccine series, 17 (18.5%) were infected with Delta and 75 (81.5%) with Omicron. Seventeen percent of participants had positive cultures beyond day 5 from symptom onset with the latest on day 12. There was no difference in time to culture conversion by variant or vaccination status. For the 14 sub-study participants, sensitivity and specificity of RDT were 100% and 86% respectively.ConclusionsThe majority of our Delta- and Omicron-infected cohort culture-converted by day 6, with no further impact of booster vaccination on sterilization or cycle threshold decay. We found that rapid antigen testing may provide reassurance of lack of infectiousness, though masking for a full 10 days is necessary to prevent transmission from the 17% of individuals who remain culture positive after isolation.Main PointBeyond day 5, 17% of our Delta and Omicron-infected cohort were culture positive. We saw no significant impact of booster vaccination on within-host Omicron viral dynamics. Additionally, we found that rapid antigen testing may provide reassurance of lack of infectiousness.

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Antigen Test Positivity After COVID-19 Isolation — Yukon-Kuskokwim Delta Region, Alaska, January–February 2022

Cited by 39 publications

References 8 publications

Evaluation of the role of home rapid antigen testing to determine isolation period after infection with SARS-CoV-2

Evaluation of the role of home rapid antigen testing to determine isolation period after infection with SARS-CoV-2

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

Viral dynamics of Omicron and Delta SARS-CoV-2 variants with implications for timing of release from isolation: a longitudinal cohort study

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