Optimal testing can reduce Covid-19 transmission

Four-panel figure comparing likelihood of onward transmission when combining negative rapid antigen test with timing of test at entrance to or exit from quarantine. (Courtesy of the authors)

New findings compare the performance of commercially available rapid antigen and rt-PCR tests for COVID-19 to assess their effectiveness in reducing transmission. Burton Singer, a UF College of Liberal Arts and Sciences mathematician with expertise in modeling disease dynamics, and an EPI faculty member, coauthored the paper which is available at medRxiv while it awaits formal publication.

The researchers built a model to compare how these various tests could be used optimally with quarantine and surveillance efforts to reduce transmission of the SARS-CoV-2 virus that causes COVID-19. Their model included data on the infectiousness of the disease’s course over time. It also included data on the specificity and sensitivity of rapid antigen and rt-PCR tests. They used the model to evaluate the optimal testing frequencies and quarantine lengths needed to reduce transmission to extremely low levels (when the virus’ effective reproduction number, Re, is less than 1).

In general, they found that both kinds of tests could be effective in reducing transmission after quarantine. (See figure above.) But the degree of transmission reduction depended upon the quarantine length, the timing of tests, and how quickly test results could be made available.  More specifically, they found:

  • Quarantines of five days or less suggest that giving a rapid antigen test when a person enters and leaves quarantine reduces onward transmission more than a single rt-PCR test given upon exit from quarantine.
  • When rt-PCR tests were conducted every six days with results available within 24-hours, and people with positive test results were isolated, onward transmission was effectively reduced.
  • Rapid antigen tests conducted every six to eight days could also significantly drive transmission down effectively to R<1.

But when results were delayed beyond 24 hours, transmission continued. They also found that false positives were more common with the rapid antigen tests than with the rt-PCR tests.

Written by: DeLene Beeland