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Performance of the Innova SARS-CoV-2 antigen rapid lateral flow test in the Liverpool asymptomatic testing pilot: population based cohort study.
García-Fiñana, Marta; Hughes, David M; Cheyne, Christopher P; Burnside, Girvan; Stockbridge, Mark; Fowler, Tom A; Fowler, Veronica L; Wilcox, Mark H; Semple, Malcolm G; Buchan, Iain.
  • García-Fiñana M; Department of Health Data Science, Institute of Population Health, University of Liverpool, Liverpool, UK martaf@liverpool.ac.uk.
  • Hughes DM; Department of Health Data Science, Institute of Population Health, University of Liverpool, Liverpool, UK.
  • Cheyne CP; Department of Health Data Science, Institute of Population Health, University of Liverpool, Liverpool, UK.
  • Burnside G; Department of Health Data Science, Institute of Population Health, University of Liverpool, Liverpool, UK.
  • Stockbridge M; Department of Health and Social Care, London, UK.
  • Fowler TA; Department of Health and Social Care, London, UK.
  • Fowler VL; William Harvey Research Institute, Queen Mary University of London, London, UK.
  • Wilcox MH; Department of Health and Social Care, London, UK.
  • Semple MG; Leeds Institute of Medical Research, University of Leeds, Leeds, UK.
  • Buchan I; NIHR Health Protection Research Unit in Emerging and Zoonotic Infections and Institute of Translational Medicine, Faculty of Health and Life Sciences, University of Liverpool, Liverpool, UK.
BMJ ; 374: n1637, 2021 07 06.
Article in English | MEDLINE | ID: covidwho-1299224
ABSTRACT

OBJECTIVE:

To assess the performance of the SARS-CoV-2 antigen rapid lateral flow test (LFT) versus polymerase chain reaction testing in the asymptomatic general population attending testing centres.

DESIGN:

Observational cohort study.

SETTING:

Community LFT pilot at covid-19 testing sites in Liverpool, UK.

PARTICIPANTS:

5869 asymptomatic adults (≥18 years) voluntarily attending one of 48 testing sites during 6-29 November 2020.

INTERVENTIONS:

Participants were tested using both an Innova LFT and a quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) test based on supervised self-administered swabbing at testing sites. MAIN OUTCOME

MEASURES:

Sensitivity, specificity, and predictive values of LFT compared with RT-qPCR in an epidemic steady state of covid-19 among adults with no classic symptoms of the disease.

RESULTS:

Of 5869 test results, 22 (0.4%) LFT results and 343 (5.8%) RT-qPCR results were void (that is, when the control line fails to appear within 30 minutes). Excluding the void results, the LFT versus RT-qPCR showed a sensitivity of 40.0% (95% confidence interval 28.5% to 52.4%; 28/70), specificity of 99.9% (99.8% to 99.99%; 5431/5434), positive predictive value of 90.3% (74.2% to 98.0%; 28/31), and negative predictive value of 99.2% (99.0% to 99.4%; 5431/5473). When the void samples were assumed to be negative, a sensitivity was observed for LFT of 37.8% (26.8% to 49.9%; 28/74), specificity of 99.6% (99.4% to 99.8%; 5431/5452), positive predictive value of 84.8% (68.1% to 94.9%; 28/33), and negative predictive value of 93.4% (92.7% to 94.0%; 5431/5814). The sensitivity in participants with an RT-qPCR cycle threshold (Ct) of <18.3 (approximate viral loads >106 RNA copies/mL) was 90.9% (58.7% to 99.8%; 10/11), a Ct of <24.4 (>104 RNA copies/mL) was 69.4% (51.9% to 83.7%; 25/36), and a Ct of >24.4 (<104 RNA copies/mL) was 9.7% (1.9% to 23.7%; 3/34). LFT is likely to detect at least three fifths and at most 998 in every 1000 people with a positive RT-qPCR test result with high viral load.

CONCLUSIONS:

The Innova LFT can be useful for identifying infections among adults who report no symptoms of covid-19, particularly those with high viral load who are more likely to infect others. The number of asymptomatic adults with lower Ct (indicating higher viral load) missed by LFT, although small, should be considered when using single LFT in high consequence settings. Clear and accurate communication with the public about how to interpret test results is important, given the chance of missing some cases, even at high viral loads. Further research is needed to understand how infectiousness is reflected in the viral antigen shedding detected by LFT versus the viral loads approximated by RT-qPCR.
Subject(s)

Full text: Available Collection: International databases Database: MEDLINE Main subject: Carrier State / COVID-19 Nucleic Acid Testing / COVID-19 Serological Testing / COVID-19 Type of study: Etiology study / Incidence study / Observational study / Prognostic study / Risk factors Topics: Long Covid Limits: Adult / Female / Humans / Male Country/Region as subject: Europa Language: English Journal: BMJ Journal subject: Medicine Year: 2021 Document Type: Article Affiliation country: Bmj.n1637

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Full text: Available Collection: International databases Database: MEDLINE Main subject: Carrier State / COVID-19 Nucleic Acid Testing / COVID-19 Serological Testing / COVID-19 Type of study: Etiology study / Incidence study / Observational study / Prognostic study / Risk factors Topics: Long Covid Limits: Adult / Female / Humans / Male Country/Region as subject: Europa Language: English Journal: BMJ Journal subject: Medicine Year: 2021 Document Type: Article Affiliation country: Bmj.n1637