SARS-CoV-2 Test Frequency, Turnaround Time Outperform Sensitivity in Curbing Virus Transmission

A mathematical modeling study concluded that when it comes to COVID-19 surveillance, test frequency and turnaround time are considerably more important than test sensitivity

The investigators determined that testing 75% of individuals every 3 days using a rapid test with a limit of detection (LOD) of 105 copies/mL and same-day results in an environment with 4% SARS-CoV-2 prevalence and a reproduction rate starting at RO 1.5 would “drive the epidemic toward extinction within 6 weeks and reduce the cumulative incidence by 88%.” In contrast, a similar testing frequency using polymerase chain reaction (PCR) with an LOD of 103 copies/mL and a 48-hour results turnaround would reduce infectiousness by 58%.

“When it comes to public health, it’s better to have a less sensitive test with results today than a more sensitive one with results tomorrow,” said lead author Daniel Larremore, in a prepared statement.

Larremore and his colleagues at the University of Colorado and Harvard University hypothesized that given the features of viral increase, infectivity, and decline during SARS-CoV-2 infection, there would be “minimal differences” in effective screening regimens between PCR tests and cheaper, faster tests with higher LODs.

The investigators modeled viral loads and infectiousness curves for 10,000 simulated individuals based on within-host viral kinetics features like latency and growth. They also assessed the impact of repeated screening at different intervals and with tests of different sensitivities in a university-type setting of 20,000 people and in a large city of 8.4 million. In addition, the researchers modeled the impact on transmission dynamics of factors such as delayed results, changed model assumptions like RO, and the effect of repeated population screening.

Even weekly testing using a test with 100 times lower molecular sensitivity than PCR with just half of a population participating would reduce the peak and length of an outbreak.

Based on their findings, the authors suggested that federal and state governments encourage the development and use of rapid, lower cost, and lower sensitivity tests for public health and repeat population screening.