Abstract
Antigen detection rapid diagnostic tests have been developed for first-line large-scale screening given their rapidity, simplicity, and accuracy. This study evaluates the diagnostic performance of an antigen detection rapid diagnostic test (BLOK BioScience, London, UK) detecting SARS-CoV-2 nucleocapsid protein. Serially diluted SARS-CoV-2 isolate and 110 NPS from COVID-19 patients were tested to determine the test’s sensitivity, and other viral isolates and 20 NPS from non-infected individuals were, for specificity, also tested. Ten clinical samples from COVID-19 patients with SARS-CoV-2 variants, including alpha, beta, gamma, delta, and eta variants, were collected to evaluate the test’s potential application in detecting emerging variants. Overall sensitivity was 92%, and stratifying into viral loads yielded 100% for Ct < 25 samples including SARS-CoV-2 variants, but 11.11% for Ct ≥ 30 samples. The analytical sensitivity of log10 TCID50/mL 2.0 was identified for SARS-CoV-2. Ninety-seven percent specificity with only SARS-CoV cross-reactivity lead to the Youden index of 0.89. The rapid diagnostic test has a high sensitivity for detecting SARS-CoV-2 in high viral load samples, possibly including emerging SARS-CoV-2 variants, but reduced sensitivity in low viral load samples suggests its optimized usage as a complementary testing method to other tests, including RT-PCR or a point-of-care test for large-scale screening, particularly for pandemic areas or airport border infection control.
Highlights
As for the false-negative results, the sample with the highest viral load that yielded negative rapid diagnostic tests (RDT) results had Ct value of 28.9, and the minimum viral load of the reverse transcription-polymerase chain reaction (RT-PCR) positive sample tested with RDT had Ct value of 37.8
The analytical sensitivity is important for the evaluation of RDT, given that the minimum viral load required for reliable detection of a positive result is clinically relevant, with each 10-fold rise in the detection limit of SARS-CoV-2 leading to an additional 13%
Positive predictive value (PPV) of RDT (BLOK BioScience) was high at 99%, and Negative predictive value (NPV) was lower due to false-negative results, yet their calculations depend on disease prevalence, which was 76% in the tested samples
Summary
December 2019, SARS-CoV-2 infections in humans were documented across all seven continents by 22 December 2020, leading to the coronavirus disease 2019 (COVID-19) pandemic with more than 245 million confirmed cases and 4.9 million deaths by 1 November 2021 that requires active interventions to prevent the continuation of spreading [8,9,10]. Given its high transmissibility with a propensity to spread in asymptomatic or presymptomatic stages due to the long incubation period reaching above 14 days [11,12,13], and the peak viral load at symptom onset [14,15,16,17], the early detection of cases of SARS-CoV-2 infection is essential to prevent further spread from infected patients, as well as permanent physical damage and long-term complications due to delayed treatment [18].
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