COVID-19 Rapid Antigen Tests Correlate With Short-term Infectiousness

By Reuters Staff

December 28, 2021

(Reuters) - Rapid antigen tests for COVID-19 might yield false negative results when viral loads are low, but in those cases, the virus may not yet be transmissible, a new study suggests.

Researchers performed rapid antigen tests on swab samples from 181 individuals with PCR-confirmed SARS-CoV-2 infections and then tried to culture the virus on the swabs. When viral loads were below the antigen tests' level of detection, the virus particles were often incapable of growing, according to a report posted on medRxiv ahead of peer review.

People with low viral loads and negative antigen tests may become infectious "a day or two or three days later," said Dr. James Kirby of Beth Israel Deaconess Medical Center in Boston. "Therefore, to be most effective, antigen tests should be used immediately before an event or contact with those at greater risk from infection."

The swabs must be collected for testing carefully, following the instructions provided with the testing kits, he added. "In other words, you want a really good sampling of the inside of your nose."

SOURCE: https://bit.ly/33RrrXk medRxiv, online December 23, 2021.

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