Performance of two rapid antigen tests against SARS-CoV-2 in neighborhoods of socioeconomic vulnerability from a middle-income country

TL;DR

This study evaluated two rapid antigen tests for SARS-CoV-2 in vulnerable neighborhoods in Brazil, finding they had high specificity but lower sensitivity than claimed, especially for people with high viral loads.

Contribution

The study provides real-world diagnostic performance data of two Ag-RDTs in a middle-income country's vulnerable population.

Findings

Both tests had 100% specificity but lower sensitivity (around 53%) compared to manufacturer claims.

Sensitivity improved to over 80% for individuals with CT values <24, indicating higher viral load.

Negative results require clinical and epidemiological context due to lower NPVs.

Abstract

As new and improved antigen-detecting rapid diagnostic tests for SARS-CoV-2 infection (Ag-RDT) continue to be developed, assessing their diagnostic performance is necessary to increase test options with accurate and rapid diagnostic capacity especially in resource-constrained settings. This study aimed to assess the performance of two Ag-RDTs in a population-based study.

We conducted a diagnostic accuracy study in neighborhoods with high socioeconomic vulnerability in Salvador-Brazil, including individuals aged ≥12 years old who attended primary health services, between July and December 2022, with COVID-19 symptoms or who had been in contact with a confirmed case. Two Ag-RDTs were compared in parallel using reverse transcription polymerase chain reaction (RT-PCR) as reference standard, the PanbioTM COVID-19 Ag test (Abbott®) and Immuno-Rapid COVID-19 Ag (WAMA Diagnostic®). Sensitivity, specificity, positive (PPV) and negative predictive values (NPV) were calculated.

For the Abbott test the sensitivity was 52.7% (95% CI: 44.3% - 61.0%), specificity 100% (95% CI: 98.7% - 100%), PPV 100% (95% CI: 95.4% - 100%) and NPV 80.4% (95% CI: 75.9% - 84.4%). For the WAMA test, the sensitivity was 53.4% (95% CI: 45.0% - 61.6%), specificity 100% (95% CI: 98.7% - 100%), PPV 100% (95% CI: 95.4% - 100%) and NPV 80.7% (95% CI: 76.2% - 84.6%). Sensitivity for the group with Cycle Threshold (CT) <24 was 82.3% (95%CI: 72.1–90.0, n = 83) for PanbioTM COVID-19 Ag test and 87.3% (95%CI: 77.9–93.8, n = 83) for Immuno-Rapid COVID-19 Ag test.

Sensitivity for both Ag-RDT was lower than reported by manufacturers. In the stratified analysis, sensitivity was higher among those with lower CT values <24. Specificity was high for both rapid antigen tests. Both Ag-RDT showed to be useful for rapid diagnostic of potential cases of COVID-19. Negative results must be assessed carefully according to clinical and epidemiological information.

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