COVID-19: Benefits of Contact Tracing Detailed

By Amy Orciari Herman

Edited by David G. Fairchild, MD, MPH, and Jaye Elizabeth Hefner, MD

Contact tracing of COVID-19 patients early in the outbreak reduced the time secondary cases were in the community by nearly 2 days, according to a retrospective analysis in the Lancet Infectious Diseases.

Researchers studied some 400 patients in China diagnosed with COVID-19 between mid-January and mid-February, plus roughly 1300 of their close contacts. During this time, intensive symptom-based surveillance, contact tracing, and isolation of cases were enforced, as were 14-day quarantine and monitoring of close contacts who tested negative for SARS-CoV-2.

Overall, cases identified through symptom-based surveillance were isolated 4.6 days after symptom onset, whereas those identified via contact tracing were isolated 2.7 days after symptoms began. Some 11% of household contacts of cases became infected, with children and adults at similar risk. Each index case caused, on average, 0.4 additional cases. Of note, an estimated 5% of cases developed symptoms 14 or more days after exposure.

The researchers caution, "The overall impact of isolation and contact tracing ... is uncertain and highly dependent on the number of asymptomatic cases. Moreover, children are at a similar risk of infection to the general population, although less likely to have severe symptoms; hence they should be considered in analyses of transmission and control."