Analytical sensitivity of the Rapid Antigen Test kits for detection of SARS-CoV-2 Omicron variant BA.2 sub-lineage

The severe acute respiratory syndrome coronavirus type 2 (SARS‐CoV‐2) Omicron was classified as a variant of concern in November 2021. The sublineage BA.2 spreads rapidly worldwide. Currently, there is a lack of data for the parallel comparison of Rapid Antigen Test (RAT) Kits to detect SARS‐CoV‐2 Omicron BA.2. We evaluated the analytical sensitivity of 12 RAT kits to detect Omicron BA.2 in the present study. Analytical sensitivity was determined by means of the limit of detection (LOD). We prepared a dilution set using a respiratory specimen collected from a COVID‐19 patient infected by Omicron BA.2. The reverse transcription‐polymerase chain reaction was used as a reference method. The LOD results showed that all 12 RAT kits had comparable analytical sensitivity to detect Omicron BA.2. The RAT kits selected in the current study may be used for the first‐line screening of the rapid spreading Omicron BA.2.

"David vs. Goliath": A simple antigen detection test with potential to change diagnostic strategy for SARS-CoV-2

INTRODUCTION

As regard to all pandemics, the current COVID-19 pandemic, could also have been better managed with prudent use of preventive measures coupled with rapid diagnostic tools such as rapid antigen tests, but their efficacy is under question because of projected lower sensitivity as compared to Real Time Reverse Transcriptase Polymerase Chain Reaction, which although considered gold standard has its own limitations.

METHODOLOGY

A prospective, single centre study was carried out to evaluate the performance of Standard Q COVID-19 Ag, a rapid immuno-chromatographic assay for antigen detection, against TrueNat, a chip-based, point-of-care, portable, Real-Time PCR analyzer for diagnosis of COVID-19; on 467 nasal swab samples from suspected subjects at a fever clinic in North India in month of July 2020.

RESULTS

Of the 467 specimens tested, TrueNat showed positive result in 29 (6.2%), majority of whom were asymptomatic (72.4%) while 4/29 (13.9%) had influenza like illness and 2/29 (6.8%) presented with severe acute respiratory illness. Compared to TrueNat, Rapid antigen test gave concordance for 26 samples, while for 2 samples the result was false positive; giving an overall sensitivity of 89.7% (95% CI = 72.6- 97.8) and a specificity of 99.5%, indicating strong agreement between two methods.

CONCLUSION

Community prevalence plays an important role is choosing the laboratory test and result interpretation. Rapid antigen detection tests definitely have a big role to play, especially in resource limited setting, for early diagnosis as well as for source control to halt the spread.

Performance Characteristics of a Rapid Severe Acute Respiratory Syndrome Coronavirus 2 Antigen Detection Assay at a Public Plaza Testing Site in San Francisco

We evaluated the performance of the Abbott BinaxNOW rapid antigen test for coronavirus disease 2019 (Binax-CoV2) to detect virus among persons, regardless of symptoms, at a public plaza site of ongoing community transmission. Titration with cultured severe acute respiratory syndrome coronavirus 2 yielded a human observable threshold between 1.6 × 10⁴-4.3 × 10⁴ viral RNA copies (cycle threshold [Ct], 30.3–28.8). Among 878 subjects tested, 3% (26 of 878) were positive by reverse-transcription polymerase chain reaction, of whom 15 of 26 had a Ct <30, indicating high viral load; of these, 40% (6 of 15) were asymptomatic. Using this Ct threshold (<30) for Binax-CoV2 evaluation, the sensitivity of Binax-CoV2 was 93.3% (95% confidence interval, 68.1%–99.8%) (14 of 15) and the specificity was 99.9% (99.4%–99.9%) (855 of 856).

Performance characteristics of a rapid SARS-CoV-2 antigen detection assay at a public plaza testing site in San Francisco

We evaluated the performance of the Abbott BinaxNOW™ Covid-19 rapid antigen test to detect virus among persons, regardless of symptoms, at a public plaza site of ongoing community transmission. Titration with cultured clinical SARS-CoV-2 yielded a human observable threshold between 1.6×104-4.3×104 viral RNA copies (cycle threshold (Ct) of 30.3-28.8 in this assay). Among 878 subjects tested, 3% (26/878) were positive by RT-PCR, of which 15/26 had a Ct<30, indicating high viral load. 40% (6/15) of Ct<30 were asymptomatic. Using this Ct<30 threshold for Binax-CoV2 evaluation, the sensitivity of the Binax-CoV2 was 93.3% (14/15), 95% CI: 68.1-99.8%, and the specificity was 99.9% (855/856), 95% CI: 99.4-99.9%.