Why Testing Speed Matters
And why the U.S. backlog is not ideal
A new study published in the journal The Lancet Public Health underscores the need for fast testing as a means to control the Covid-19 pandemic. The researchers of the study used mathematical modeling to determine the effectiveness of conventional and app-based contact tracing strategies on Covid-19 transmission. They conclude that the speed of testing is the most important factor for successful contract tracing, and quelling the spread of Covid-19. If Covid-19 testing is delayed by even just three days or more after a person develops symptoms, the researchers say that even the most thorough contact tracing strategy will come up short. The study authors distilled their findings in a press release about the findings, and I’m sharing those findings here (R refers to R0 or “R-naught,” an indicator of how easily a disease spreads from person to person in a community):
- Even if all contacts are successfully traced, a delay of three days or more between symptom onset and testing will not reduce onward transmission of the virus sufficiently to control further spread, according to modeling study.
- In the best-case scenario, with zero delays and at least 80% of contacts traced, the R number is reduced from 1.2 to around 0.8, and 80% of onward transmission per person diagnosed could be prevented.
- For conventional contact tracing to work, test results need to be delivered within a day of an individual developing symptoms.
- Mobile apps can speed up contact tracing and keep R below 1, even if only 20% of the population uses them.
While this study offers helpful information for understanding how to better control the spread of Covid-19, unfortunately the United States is experiencing yet another backlog in tests. Some people are waiting well over a week to get their results back. If speed is indeed one of the most important factors for effective transmission control, then the United States is not well positioned for success right now.
“Turnaround time matters a lot,” Yonatan Grad, MD, PhD, assistant professor of immunology and infectious diseases and a faculty member in the Center for Communicable Disease Dynamics at Harvard University said in a recent presser. “You have to be able to identify cases quickly, and not only for the purposes of contact tracing but generally for management of an epidemic. You really need to move quickly to identify those individuals and place them into quarantine or test them and if they’re positive praise escalation to work to address the spread of infection. The slower the turnaround the less success you’re going to have.”