Hong Kong Med J . Rapid antigen test during a COVID-19 outbreak in a private hospital in Hong Kong

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Hong Kong Med J


. 2022 Mar 17.
doi: 10.12809/hkmj219559. Online ahead of print.
Rapid antigen test during a COVID-19 outbreak in a private hospital in Hong Kong


J S T Zee ^{1 2} , C T L Chan ¹ , A C P Leung ¹ , B P W Yu ² , J R L **** ² , Q W L Chan ² , E S K Ma ¹ , K H Lee ³ , C C Lau ³ , R W H Yung ^{1 2 3}



Affiliations

• PMID: 35307652
• DOI: 10.12809/hkmj219559

Abstract

Introduction: In response to two nosocomial clusters of coronavirus disease 2019 (COVID-19) in our hospital, we adopted a series of strict infection control measures, including regular rapid antigen test (RAT) screening for high-risk patients, visitors, and healthcare workers. We evaluated the diagnostic performance of a locally developed RAT, the INDICAID COVID-19 Rapid Antigen Test (Phase Scientific, Hong Kong), using respiratory samples from both symptomatic and asymptomatic individuals.
Methods: Real-time reverse-transcription polymerase chain reaction (rRT-PCR)-confirmed deep throat saliva (DTS) and pooled nasopharyngeal swab and throat swab (NPS/TS) samples collected from 1 November to 30 November 2020 were tested by INDICAID. Screening RATs were performed on asymptomatic healthcare workers during a 16-week period (1 December 2020 to 22 March 2021).
Results: In total, 20 rRT-PCR-confirmed samples (16 DTS, four pooled NPS/TS) were available for RAT. Using the original sample, RAT results were positive in 17/20 samples, indicating 85% sensitivity (95% confidence interval [CI]=62.11%-96.79%). Negative RAT results were associated with higher cycle threshold (Ct) values. For samples with Ct values <25, the sensitivity was 100%. Of the 49 801 RATs collected from healthcare workers, 33 false positives and one rRT-PCR-confirmed case were detected. The overall specificity was 99.93% (95% CI=99.91%-99.95%). The positive and negative predictive values were 2.94% (95% CI=2.11%-4.09%) and 100%, respectively.
Conclusion: The INDICAID COVID-19 RAT demonstrated good sensitivity for specimens with high viral loads and satisfactory specificity for low-risk, asymptomatic healthcare workers.

Keywords: COVID-19; Mass screening; SARS-CoV-2.