Extensive contact tracing, isolation key to control COVID-19 spread, says study

Extensive contract tracing, isolating cases, and testing may reduce the spread of the novel coronavirus, a study carried out in China has suggested.

The impact of contact tracing, however, depends on identifying asymptomatic cases.

The new study, published in The Lancet Infectious Diseases journal, found that contact tracing increased the speed at which new cases were confirmed by two days -- an average of 5.5 days initially, reduced to 3.2 with contact tracing. It also reduced the amount of time it took to isolate infected people by two days -- from an average of 4.6 days down to 2.7.

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The length of time for which a person remains infectious is not yet known, but reducing the amount of time that infected people interacted with others appears to have helped reduce the virus spreading, the researchers said.

For the current study, the researchers analysed data from 391 people diagnosed with COVID-19 after they showed symptoms, and 1,286 of their close contacts. The contacts were tested irrespective of whether they had symptoms in order to identify infected people who were asymptomatic.

The study found that contact tracing reduced the length of time people were infectious in the community over 4 weeks in Shenzhen, China.

According to results from In Shenzhen, authorities identified whom to isolate based on their contact with confirmed cases, as well as isolating people who already had symptoms.

There were only three deaths in the study group during the study period, the researchers said.

To achieve similar results, the researchers noted that other countries might be able to combine near-universal testing and intensive contact tracing with social distancing and partial lockdowns.

Although no lockdown measures were introduced in Shenzhen until the end of the study period, Wuhan's lockdown could have significantly restricted the spread of coronavirus to Shenzhen.

Close contacts were defined as people who shared a household with infected patients up to 2 days before they started showing symptoms, or interacted with them socially by travelling or eating together.

For people who were isolated because they showed symptoms of COVID-19, it took an average of 4.6 days for them to be isolated following the first signs of infection. Contact tracing reduced this to an average of 2.7 days.

For people diagnosed with COVID-19 after being contact traced and tested (87 people), a fifth (17 out of 87 people) had not yet developed any symptoms, and 30 per cent (25 out of 87) did not have a fever.

Their contacts might, however, have been missed if they were asymptomatic, because the PCR test is not sensitive enough to pick up every case, according to the researchers.