Accuracy of COVID-19 self-tests with unsupervised nasal or nasal plus oropharyngeal self-sampling in symptomatic individuals in the Omicron period

Abstract

Background Performances of rapid antigen diagnostic tests (Ag-RDTs) with nasal self-sampling, and oropharyngeal plus nasal (OP-N) self-sampling, in the Omicron period are unknown. Methods Prospective diagnostic accuracy study among 6,497 symptomatic individuals aged ≥16 years presenting for SARS-CoV-2 testing at three test-sites. Participants were sampled for RT-PCR (reference test) and received one Ag-RDT to perform unsupervised with either nasal self-sampling (during the emergence of Omicron, and after Omicron share was >90%, phase-1) or with OP-N self-sampling (in a subsequent phase-2; Omicron share >99%). The evaluated tests were Acon Flowflex (Flowflex; phase-1 only), MP Biomedicals (MPBio), and Siemens-Healthineers Clinitest (Clinitest). Findings During phase-1, 45% of Flowflex, 29% of MPBio, and 35% of Clinitest participants were confirmatory testers (previously tested positive by a self-test at own initiative). Overall sensitivities with nasal self-sampling were 79.0% (95% CI: 74.7-82.8%) for Flowflex, 69.9% (65.1-74.4%) for MPBio, and 70.2% (65.6-74.5%) for Clinitest. Sensitivities were substantially higher in confirmatory testers (93.6%, 83.6%, and 85.7%, respectively) than in those who tested for other reasons (52.4%, 51.5%, and 49.5%, respectively). Sensitivities decreased by 6.1 (p=0.16 by Chi-square test), 7.0 (p=0.60), and 12.8 (p=0.025) percentage points, respectively, when transitioning from 29% to >95% Omicron. During phase-2, 53% of MPBio, and 44% of Clinitest participants were confirmatory testers. Overall sensitivities with OP-N self-sampling were 83.0% (78.8%-86.7%) for MPBio and 77.3% (72.9%-81.2%) for Clinitest. Comparing OP-N to nasal sampling, sensitivities were slightly higher in confirmatory testers (87.4% and 86.1%, respectively), and substantially higher in those testing for other reasons (69.3% and 59.9%, respectively). Interpretation Sensitivities of three Ag-RDTs with nasal self-sampling decreased during Omicron emergence but was only statistically significant for Clinitest. Sensitivities were substantially influenced by the proportion of confirmatory testers. Addition of oropharyngeal to nasal self-sampling improved sensitivities of MPBio and Clinitest. Funding Dutch Ministry of Health, Welfare, and Sport.

Diagnostic accuracy of SARS-CoV-2 rapid antigen self-tests in asymptomatic individuals in the Omicron period: cross sectional study

“…We observed a similar trend in symptomatic individuals for Clinitest but not for MPBio. (2) This study is to our knowledge the largest empirical SARS-CoV-2 self-test diagnostic accuracy study among asymptomatic individuals in the Omicron period. Additional strengths include the large numbers of participants recruited at multiple test sites nationwide, the low percentage of missing values, RT-PCR reference test sampling and unsupervised Ag-RDT self-testing by the same individuals within a few hours conform the real-world context of self-testing, blinding of participants for the reference test result and blinding of laboratory staff for the Ag-RDT self-test result, and the use of a viral load cut-off.…”

“…(1,4,11) In addition, it might be more difficult for asymptomatic individuals to self-retrieve sufficient nasal fluid by selfswabbing because of the absence of rhinorrhea. Addition of oropharyngeal self-sampling to the currently applied nasal self-sampling might have led to higher Ag-RDT sensitivities (2,12), but it is very unlikely that the sensitivities would have reached acceptable levels. Finally, we cannot entirely exclude that some of the discordant results (Ag-RDT negative, RT-PCR positive) can be attributed to an undetected prior SARS-CoV-2 infection -in which RT-PCR remain positive for a prolonged period of time -rather than a newly acquired infection.…”

Availability and Advice on Test uptake: a vignette study on Covid-19 self-testing policy.

“…Limitations are that this is, ultimately, a vignette study using expected behaviour as an outcome and that conclusions are based on assumptions about the sensitivity of PCR and self-tests. As self-tests may be somewhat less sensitive for Omicron than Delta 24 , this could affect the relevance of the results. However all results were similar when we assumed a 10% lower sensitivity scores for self-tests than Delta sensitivity scores.…”