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1/ As COVID-19 cases continue to surge, a missing testing metric can help explain the ineffectiveness of our containment efforts. The public discussion around testing has been relating to testing volume, but turnaround time (TAT) is at least as important as volume. (THREAD)
2/ One of the key developments over the past few months is understanding the high level of asymptomatic (or pre-symptomatic) positives in the population.
3/ As we published a week ago, close to 80% of positives we are finding exhibit mild or no symptoms. There is also evidence that individuals are most contagious right before or at symptom onset. https://www.color.com/new-covid-19-test-data-majority-of-people-who-test-positive-for-covid-19-have-mild-symptoms-or-are-asymptomatic
4/ So, many individuals will spread the virus BEFORE developing symptoms (especially because we can be reasonably effective at isolating people once they’re obviously sick).
6/ This means that rapid turnaround on testing for mitigation/surveillance is fundamental to the value of testing. The primary purpose of testing for mitigation is so that you can identify individuals who are infected, but not yet showing symptoms, before they infect others.
7/ Telling someone that they were an asymptomatic positive 5 days ago is close to worthless - by then, they have already done the damage.
8/ @michaelmina_lab told @TheAtlantic “if you don’t get results back in a day or so, outbreaks really can’t be stopped without isolating and quarantining all contacts preemptively.” https://www.theatlantic.com/science/archive/2020/06/us-coronavirus-testing-could-fail-again/613675/
9/ A recent pre-print from @michaelmina_lab, @DanLarremore, et al found TAT and frequency of testing are more important for controlling outbreaks than analytic test sensitivity (limit of detection). A rapid TAT (0-1 days) is necessary to control outbreaks. https://www.medrxiv.org/content/10.1101/2020.06.22.20136309v2
10/ Comparing TAT of 0-2 days, different testing cadences (daily, 3 days, weekly & 14-days) and the limit of detection for tests, they found a 0-1 day TAT and/or frequent testing can keep the R0 below 1, controlling the epidemic.
11/ When TAT is 3+ days, the R0 rises above 1, sustaining the outbreak. Because people are not self-isolating while waiting for results, we increase the number of cases and make contract tracing more difficult.
12/ Sidenote: self-isolation while waiting for results places an economic burden on individuals who need to work and decreases the chance people are willing to get tested. This story from Dallas shows the importance of rapid turnaround on testing. https://www.nbcdfw.com/news/coronavirus/covid-19-test-results-taking-a-week-or-more-for-some/2397875/
13/ tl;dr: While test sensitivity does have an impact on R0, it can be offset by more frequent testing and/or faster TAT. Delays result in greater distribution and higher levels of infectiousness in individuals.
14/ This is why TAT is something we ( @color) prioritized since the beginning of our COVID-19 work. In June, while our volume more than tripled, 42% of COVID-19 results were released in under 24 hours, and 89% were released in under 48 hours - and we still need to do better.
15/ As we move into the next phase of the crisis, public health efforts need to consider a way to quantify the value/cost of long wait times for results. Four months into the crisis, national labs showing week-long TAT’s is a huge problem that needs to be resolved.
16/ Have a safe 4th of July weekend. Stay safe, don’t be too social and make sure to wear a mask!
