Rapid COVID Tests Reliable in Close Contacts Without Symptom
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Two widely used SARS-CoV-2 rapid antigen tests can reliably be used to test close contacts for infectiousness from the fifth day after infection, even when have not yet developed symptoms, according to a Dutch study. The Veritor and Biosensor lateral-flow rapid SARS-CoV-2 antigen tests are used by the Dutch public health service in people with mild to moderate symptoms of COVID-19 with no requirement for retesting with reverse-transcriptase polymerase chain reaction (PCR).

Less is known about their reliability in asymptomatic or presymptomatic close contacts of COVID-19 patients, researchers explain in The BMJ. To investigate, they assessed the diagnostic accuracy of the two tests on the fifth day after exposure to an index case in 4,274 close contacts (identified through the test-and-trace program or contact-tracing app) aged 16 years or older and asymptomatic for COVID-19.

The sensitivity of both tests for detecting SARS-CoV-2 in this population topped 60% and increased to more than 85% after a viral-load cut-off was applied as a proxy of infectiousness, report Dr. Karel Moons of University Medical Center Utrecht, in the Netherlands, and colleagues. "Specificities and positive and negative predictive values were high in analyses for both tests," they note.

"The results suggest that close contacts of people with confirmed SARS-CoV-2 infection can accurately be tested for SARS-CoV-2 using either rapid antigen test from day five onwards, even when they have not (yet) developed symptoms," they write. However, these rapid antigen tests "should not be used when the consequences of missed infections will be severe," they note.