Rates of rapid antigen test positivity after day 5 from a positive COVID-19 test

A recent study posted to the medRxiv* preprint server evaluated the positivity rates of coronavirus disease 2019 (COVID-19) rapid antigen tests (RAT) in infected individuals.

Study: Evaluation of the role of home rapid antigen testing to determine isolation period after infection with SARS-CoV-2. Image Credit: nito/Shutterstock
Study: Evaluation of the role of home rapid antigen testing to determine isolation period after infection with SARS-CoV-2. Image Credit: nito/Shutterstock

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

 

Background

The latest COVID-19 isolation guidelines announced by the United States (US) Centers for Disease Control (CDC) revised the isolation period to five days for non-immunocompromised people developing an asymptomatic or mild infection. The infected individuals must use tight-fitting face masks near other people during this period.

According to some studies, the risk of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) transmission is higher one day before the onset of symptoms and up to three days post-symptom-onset. While these results correspond to the period preceding the emergence of the SARS-CoV-2 Omicron variant, there is limited knowledge regarding the infectious phase of an individual in the Omicron period, given its enhanced transmissibility and extensive vaccination rates. Moreover, the optimal isolation duration for infected people is uncertain.

The study

The present study assessed the performance of RATs after five days of initial confirmed COVID-19 diagnosis by quantifying the test positivity rate and correlating the findings with symptoms and viral culture positivity. Between January 5, 2022, and February 11, 2022, SARS-CoV-2-positive study participants wanting to return to work/campus within ten days of COVID-19 diagnosis were provided with home RAT kits. These participants could return if they remain asymptomatic and/or afebrile for 24 hours with a negative RAT result on any day after five days of initial diagnosis.

The participants were adults (≥18 years) affiliated with the Broad Institute of MIT and Harvard reporting a new COVID-19-positive test. They self-tested with the Flowflex RAT, which is approved for emergency use in asymptomatic infections, and were required to provide pictures of test results in addition to reporting symptoms until they were RAT-negative.

Findings

The researchers enrolled 40 individuals with a new COVID-19 diagnosis during the study period. The mean age of the participants was 32 years, and females constituted about 58% of them. All participants were vaccinated, with about 90% receiving a booster vaccine dose. Most (83%) individuals developed symptoms approximately 1.2 days before testing positive, and no participant required hospitalization. Cycle threshold (Ct) values were available for 29 individuals tested at the Broad Institute with quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The mean Ct value was 26.5, and the median Ct was 28.9.

Ten participants had a negative RAT result on the sixth day; daily positive results declined steadily, and all participants were RAT-negative by day 14. There was no correlation between the first RAT-negative result and time, or time since vaccination and RAT result, and Ct value. Throughout the study period, 90 RATs were performed from the sixth day, and of these, 68% were positive; 10 participants asymptomatic on the sixth day were RAT-positive.

Anterior nasal (AN) and oral swabs were obtained from 17 individuals on the sixth day for the SARS-CoV-2 culture tests. Eight individuals were asymptomatic, 12 subjects were concurrently RAT-positive, and the remaining had a negative result. Six individuals were positive for viral culture and were contemporaneously RAT-positive on that day. Two of them were asymptomatic throughout, with two individuals reporting symptom improvement on day six and two others declaring no change in symptomology. The positive predictive value (PPV) for a symptomatic case with a positive RAT result being culture-positive was 57%. On the sixth day, the negative predictive value (NPV) was 100% for asymptomatic people with a RAT-negative result.

Conclusions

The authors noted that in the cohort of 17 participants with virus culture results, incorporating negative RAT results (with the culture-negative status as a proxy) for ending the isolation period would mean six individuals being isolated longer than needed. A strategy based on improving symptoms alone could risk the premature release of four infectious individuals with positive virus cultures and two individuals in (prolonged) isolation. Based on a negative RAT for asymptomatic cases, one individual would have been released, and the number of people in prolonged isolation could have been minimized to three.

Understanding the risk of transmission in the early stages of infection is critical to guiding policies for containing viral spread and lowering the isolation period for non-infectious individuals. The team observed that 75% of the participants were positive with RAT five days after SARS-CoV-2 infection, and one-third were positive on day 10 of COVID-19 diagnosis. RAT and viral culture positivity rates were poorly correlated with 50% PPV, while a strong correlation was noted with RAT negative results (NPV = 100%).

The sample size was small and included young, healthy vaccinated subjects with a mild infection, presumably the SARS-CoV-2 Omicron variant. Hence, these findings are likely to vary among older people depending on vaccination status and comorbidities. In conclusion, ending isolation on day six of infection could risk the premature release of infectious, virus culture-positive individuals.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

Journal references:

Article Revisions

  • May 12 2023 - The preprint preliminary research paper that this article was based upon was accepted for publication in a peer-reviewed Scientific Journal. This article was edited accordingly to include a link to the final peer-reviewed paper, now shown in the sources section.
Tarun Sai Lomte

Written by

Tarun Sai Lomte

Tarun is a writer based in Hyderabad, India. He has a Master’s degree in Biotechnology from the University of Hyderabad and is enthusiastic about scientific research. He enjoys reading research papers and literature reviews and is passionate about writing.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Sai Lomte, Tarun. (2023, May 12). Rates of rapid antigen test positivity after day 5 from a positive COVID-19 test. News-Medical. Retrieved on July 21, 2024 from https://www.news-medical.net/news/20220309/Rates-of-rapid-antigen-test-positivity-after-day-5-from-a-positive-COVID-19-test.aspx.

  • MLA

    Sai Lomte, Tarun. "Rates of rapid antigen test positivity after day 5 from a positive COVID-19 test". News-Medical. 21 July 2024. <https://www.news-medical.net/news/20220309/Rates-of-rapid-antigen-test-positivity-after-day-5-from-a-positive-COVID-19-test.aspx>.

  • Chicago

    Sai Lomte, Tarun. "Rates of rapid antigen test positivity after day 5 from a positive COVID-19 test". News-Medical. https://www.news-medical.net/news/20220309/Rates-of-rapid-antigen-test-positivity-after-day-5-from-a-positive-COVID-19-test.aspx. (accessed July 21, 2024).

  • Harvard

    Sai Lomte, Tarun. 2023. Rates of rapid antigen test positivity after day 5 from a positive COVID-19 test. News-Medical, viewed 21 July 2024, https://www.news-medical.net/news/20220309/Rates-of-rapid-antigen-test-positivity-after-day-5-from-a-positive-COVID-19-test.aspx.

Comments

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment
Post

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
In-hospital delirium linked to long-term cognitive impairment in COVID-19 patients over 60