LAUSR

Objectives PCR on nasopharyngeal exudates, the cornerstone of the detection of SARS-CoV-2, is time-consuming and commonly unavailable at primary health care centres. Detection of viral nucleocapsid antigens using lateral flow point-of-care tests is helpful for the early triage of patients who attend health care facilities. Methods Prospective study carried out in clinically suspected cases and close asymptomatic contacts who attended a primary care centre (Madrid, Spain) for SARS-CoV-2 detection. Patients were divided into three 300-patient cohorts (n=200 symptomatic cases and n=100 close asymptomatic contacts per cohort). Three antigen detection tests (SGTI-Flex COVID-19 Ag, PanbioTM COVID-19 Ag Rapid Test Device, and GSD NovaGen SARS-CoV-2 Ag Rapid Test) were used and compared. Paired nasopharyngeal exudates were obtained, one swab for PCR and the other for antigen detection. Each antigen detection test was evaluated on one cohort. Results All tests showed invariably 100% specificity. Sensitivity in clinically suspected patients was 68.9% (95 %CI: 55.7 - 80) (SGTI-Flex), 71.1% (95 %CI: 55.6 - 83.6) (PanbioTM), and 84.6% (95 %CI: 72 - 93.1) (NovaGen) and 84.6% (95 %CI: 54.5 - 98.1), 33.3% (95 %CI: 11.8 - 61.6), and 55.6% (95 %CI: 30.7 - 78.4) in close asymptomatic contacts, respectively. Sensitivity was systematically higher in samples yielding positive PCR results with Ct ≤20. Conclusions We found considerable test-to-test antigen detection variations among patients with clinical suspicion of COVID-19 and close asymptomatic contacts. Negative antigen results, regardless the test used, should be confirmed by PCR.