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Reducing Testing Delay Crucial for Slowing COVID-19 Transmission

Model shows most efficient strategy cannot reduce R to less than 1 with testing delay of three or more days

MONDAY, July 20, 2020 (HealthDay News) -- Minimizing testing delay has the largest impact on reducing onward transmission of COVID-19, according to a study published online July 16 in The Lancet Public Health.

Mirjam E. Kretzschmar, Ph.D., from the University Medical Center Utrecht in the Netherlands, and colleagues examined the impact of a contact tracing strategy for COVID-19 using a stochastic mathematical model. The effective reproduction numbers of a contact tracing strategy (RCTS) were computed for a population with physical distancing measures and various scenarios for tracing and quarantine.

The researchers found that the estimated effective reproduction number of 1.2 could be reduced to 0.8 by adding contact tracing for the most optimistic scenario (testing and tracing delays of zero days and tracing coverage of 100 percent) and assuming that about 40 percent of transmissions occur before symptom onset. When testing and tracing coverage are reduced to 80 percent, a similar reduction could be achieved. To keep the RCTS values below 1, a testing delay of more than one day required the tracing delay to be at most one day or tracing coverage to be at least 80 percent. Even the most efficient strategy cannot reach an RCTS less than 1 with a testing delay of three days or longer. With decreasing coverage of app use, the effect of minimizing tracing delay declined; however, even with 20 percent coverage, app-based tracing remains more effective than conventional tracing.

"An optimized contact tracing strategy, with short delays and high coverage for testing and tracing, could substantially reduce the reproduction number, which would allow alleviation of more stringent control measures," the authors write.

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