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Rapid antigen testing for COVID-19 has largely replaced RT-PCR testing in the ambulatory setting, but accuracy data are limited. Dutch investigators performed a prospective assessment of rapid antigen testing at public testing facilities using self-collected nasal or nasal plus oropharyngeal swabs; three commercial kits were compared with RT-PCR.
In all, 6497 individuals were enrolled from December 21, 2021, to February 10, 2022, a period when the proportion of SARS-CoV-2 infections caused by Omicron rose from 29% to 99% in the Netherlands. The sensitivities for nasal samples with the three kits ranged from 77%–86% over the entire study period, but this range fell to 70%–81% when Omicron became predominant. For the two assays with combined oropharyngeal and nasal testing, the samples had up to 10% higher sensitivity over nasal samples alone. Subset analysis found an increase in sensitivity for individuals having a confirmatory rapid antigen test secondary to a prior positive test, and a slight decrease in sensitivity for individuals with previous COVID-19.
Schuit E et al. Diagnostic accuracy of covid-19 rapid antigen tests with unsupervised self-sampling in people with symptoms in the omicron period: Cross sectional study. BMJ 2022 Sep 14; 378:e071215. (https://doi.org/10.1136/bmj-2022-071215)
Comment
This large study shows that three different rapid antigen tests had similar sensitivities against the original Omicron variant, from which the BA.4 and BA.5 variants have evolved. That 20% to 30% of infections were missed with a single test is in keeping with more recent anecdotal reports; indeed, the current FDA guidance states that individuals who have COVID-19 symptoms should perform two or three antigen tests spaced every 48 hours if the initial test(s) are negative. The authors note that the lower sensitivity seen in individuals with prior infection could be related to either a lower viral load in subsequent infections or test interference linked to the presence of circulating anti-nucleocapsid protein antibodies.