Reliability of SARS-CoV-2 Rapid Antigen Tests
SARS-CoV-2 rapid antigen tests have been touted as having the potential to significantly reduce the spread of COVID19, if used regularly by a high percentage of the population. However, experimental and observational studies have not shown them to be effective.
A preprint study recently posted to medRxiv raised even more questions about the reliability of at-home rapid antigen tests in the early days of infection with the highly mutated Omicron variant. The small real-world study examined test results from 30 people who were tested with either Abbott BinaxNOW or Quidel QuickVue rapid antigen tests and RT-PCR on a daily basis. Nasal samples were collected for rapid antigen testing and saliva was collected for RT-PCR.
On days 0 and 1 following a positive PCR test, the at-home rapid antigen tests produced false-negative results despite the presence of viral loads high enough for transmission. RT-PCR cycle threshold (Ct) values for the N gene target ranged between 23 and 28.
On average, it took 3 days for people to test positive on a rapid antigen test after testing positive on a PCR test. At least four of the people with false negative test results transmitted SARS-CoV-2 to others.
This small study suggested that rapid antigen tests might not prevent community spread of SARS-CoV-2 even if they were readily available.
Reference
Adamson B et al. Discordant SARS-CoV-2 PCR and Rapid Antigen Test Results When Infectious: A December 2021 Occupational Case Series, medRXIV, January 5, 2022, doi: https://doi.org/10.1101/2022.01.04.22268770
