ABSTRACT
Background. Omicron rapidly replaced delta as the predominant strain causing COVID-19 related illness in the United States (US) in December 2021, the same month the US CDC reduced the recommended isolation period from 10 to 5 days for asymptomatic individuals or those with resolving symptoms. New evidence suggests some asymptomatic individuals with omicron remain culture positive beyond 5 days from diagnosis. We sought to evaluate the performance of a SARS-CoV-2 antigen rapid diagnostic test (RDT) in predicting persistent potential for transmission at the end of a five-day isolation period among young, fully vaccinated individuals in a university community setting. Methods. A subgroup of participants enrolled in a longitudinal COVID-19 cohort were asked to self-perform RDTs on days 4 to 6 from diagnostic test date in addition to a separate self-collected anterior nasal swab used for culture and RT-PCR, and a daily symptom screen (15 COVID-19 symptom questions on a 4-point scale). We calculated the daily and overall sensitivity and specificity of the RDTs in comparison to SARS-CoV-2 culture result. We also compared the N1 cycle threshold (CT) values and symptom score on each day of the study by RDT results. Results. Of 23 participants, the mean age was 20 years, all had completed their primary COVID-19 vaccine series, and 13 (65.0%) had received a booster vaccine (Table 1). Compared to culture, sensitivity and specificity of the RDTs were 100% and 62% respectively (Table 2). Compared to participants with negative RDTs, median CT values were lower in those with positive RDTs on each day of the study (Figure 1). Participants who had positive RDTs on all three days had higher symptom scores (Figure 2) than those without. Conclusion. RDTs have a high sensitivity in detecting culture positive SARS-CoV-2 on Days 4 to 6 from initial diagnostic test. However, the high false positive rate of 38% means that over a third of culture negative individuals will stay in isolation longer than necessary if RDTs are used in test to release from isolation protocols. Viral loads (CT values) and symptom scores were higher for participants with persistently positive RDT result. An approach that uses a combination of RDTs, CT values and symptom score may prove useful in guiding isolation duration.
ABSTRACT
Background. Vaccination is a fundamental element of pandemic control;however, insufficient data exists on vaccine's impact on SARS-CoV-2 viral dynamics. We aimed to evaluate the relationship between time to negative viral culture conversion after diagnosis and time since most recent COVID-19 vaccination. Scatterplot illustrating relationship between time since completion of initial COVID-19 vaccine series and time to culture conversion among un-boosted participants. The vaccine type received has also been designated by plot labels. The black solid line shows the best fit for the Spearman correlation model;gray shading denotes 95% confidence interval around this estimate. Spearman correlation coefficient, R, and p-value were estimates for the model. Methods. CoViD Post-vax is longitudinal cohort study collecting baseline clinical questionnaires, and daily anterior nasal swabs and symptom screens on enrolled Boston University SARS-CoV-2 PCR-positive cases detected through a serial screening testing program or symptomatic testing. Data was collected from November 2021 to March 2022. Participants were excluded from analysis if they lacked at least one positive culture or did not culture convert during their study involvement. Scatter plots comparing time to culture conversion to time from initial vaccine series were created.We calculated spearman correlation coefficients to determine the relationship between time to culture conversion and time from last vaccination for all participants, those who completed the initial vaccine series (unboosted), and those who were boosted. Scatterplot illustrating relationship between time since receiving a booster COVID-19 vaccine dose and time to culture conversion among boosted participants. The vaccine type received has also been designated by plot labels. The black solid line shows the best fit for the Spearman correlation model;Gray shading denotes 95% confidence interval around this estimate. Spearman correlation coefficient, R, and p-value were estimates for the model. Results. Of 54 CoViD Post-Vax participants included in this analysis, the mean age was 21 years (SD=2) and culture conversion occurred after a median of 4 days (IQR=3-5.75). There was no association between time to culture conversion and time since last dose of a COVID-19 vaccination (R= -0.13, p= .34). When stratified by vaccination status, there was no association between time to culture conversion and time since initial COVID-19 vaccine series (R= -0.25, p= .21, n=26) or time since COVID-19 booster vaccination (R= -0.24, p= .22, n=28). Conclusion. Our results show no significant relationship between time to culture conversion and time since most recent dose of COVID-19 vaccination in an initially culture positive, young, University-based cohort. More work needs to be done to understand the impact of symptom severity, disease burden, SARS-CoV-2 variants, and COVID-19 vaccine status on duration of transmissible SARS-CoV-2 infection. (Figure Presented).