Acute-phase coronavirus rapid antigen test

Now available from BioConnections, COVID-19 Ag Respi-Strip detects the presence of SARS-CoV-2 antigens in a nasopharyngeal swab in 15 minutes in more than seven out of 10 patients with the high viral load (Cycle threshold [Ct] <25; an inverse measure of the target [virus] concentration) found in the acute phase of COVID-19.

As Ag Respi-Strip is a simple to perform lateral-flow assay that is rapid and requires no equipment, it can be used anywhere with appropriate safeguards.  Hospitals with laboratories offering 24-hour service for any of the pathology disciplines should be able to process and report a sample in 30 minutes.

An algorithm is proposed whereby patients are screened with Ag Respi-Strip. Decisions concerning isolation and cohorting can be made on positive results, while negative results are submitted for qPCR.

The product has been developed with the co-operation of scientists from several European countries.  Analytical and clinical trials have taken place in Belgium, where the product is manufactured, with satisfactory results.

For the analytical study, 400 observations were recorded using stored samples submitted in transport swabs for qPCR.  This study showed between-observer agreement of 98.3%, and a high level of user friendliness.  There were no cross-reactions when tested against 30 nasopharyngeal swabs infected with other viral pathogens, giving a specificity of 100%.

A multi-centre clinical study was performed based on tests direct from 328 nasopharyngeal swabs in three clinical laboratories.  Overall sensitivity was 57.6% while sensitivity on samples with Ct <22 was 95% and most importantly the positive predictive value was 98.7%.

An algorithm is proposed which utilises Ag Respi-Strip to flag up the patients with a high SARS-Cov-2 viral load within 30 minutes of the sample reaching the laboratory. Negative Ag Respi-Strip samples are forwarded for qPCR testing and results will be available in 24–48 hours.

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