COVID-19: Contact Tracing, Isolation Have Impact, Study Shows

Richard Mark Kirkner

April 29, 2020

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A far-reaching surveillance initiative was implemented in Shenzhen, China, to isolate and contact trace people suspected of having the COVID-19 coronavirus. This initiative led to faster confirmation of new cases and reduced the window of time during which people were infectious in the community. This potentially reduced the number of new infections that arose from each case, according to a study of patients and contacts over 4 weeks (Lancet Infect Dis. 2020 Apr 27. doi: 10.1016/S1473-3099[20]30287-5).

"The experience of COVID-19 in the city of Shenzhen may demonstrate the huge scale of testing and contact tracing that's needed to reduce the virus spreading," said study coauthor Ting Ma, PhD, of Harbin Institute of Technology at Shenzhen.

Dr. Ma acknowledged that some of the measures the program used, such as isolating people outside their homes, may be difficult to impose in other countries, "but we urge governments to consider our findings in the global response to COVID-19."

The study followed 391 coronavirus cases and 1,286 close contacts identified by the Shenzhen Center for Disease Control and Prevention from Jan. 14 to Feb. 12 this year. The study showed that contact tracing led to confirming new diagnoses within 3.2 days on average vs. 5.5 for symptom-based surveillance, and reduced the time it took to isolate newly infected people by 2 days, from an average of 4.6 to 2.7 days.

Eighty-seven people were diagnosed with COVID-19 after they were contact traced and tested. Twenty percent of them had no symptoms, and 29% had no fever. Three deaths occurred in the group during the study period.

The surveillance program was comprehensive and intense. On Jan. 8, the Shenzhen CDC started monitoring travelers from Hubei province, of which Wuhan is the capital, for symptoms of COVID-19. Shenzhen is a city of about 12.5 million people in southeastern China, near Hong Kong, and is about 560 miles south of Wuhan. Over the next 2 weeks, the Shenzhen CDC expanded that surveillance program to all travelers from Hubei regardless of symptoms, along with local hospital patients and people detected by fever screenings at area clinics.

Suspected cases and close contacts underwent nasal-swab testing at 40 different locations in the city. The program identified close contacts through contact tracing, and included anyone who lived in the same dwelling, shared a meal, traveled, or had a social interaction with an index 2 days before symptoms appeared. Casual contacts and some close contacts, such as clinic nurses, who wore masks during the encounters were excluded.

"To achieve similar results, other countries might be able to combine near-universal testing and intensive contact tracing with social distancing and partial lockdowns," said Dr. Ma. "Although no lockdown measures were introduced in Shenzhen until the end of our study period, Wuhan's lockdown could have significantly restricted the spread of coronavirus to Shenzhen."

The researchers noted that children are as susceptible to the virus as are adults, even though their symptoms are not as severe as those of adults. The rate of infection in children 10 and younger was similar to the overall infection rate, 7.4% vs. 6.6%, so the researchers noted that surveillance measures should target them as well.

"This study to me confirms a lot of what we've already known," Aaron E. Glatt, MD, chairman of medicine and an epidemiologist at Mount Sinai South Nassau in Oceanside, N.Y., said in an interview. "It's an elegant study, but at the same time it sends us a message that we're at a critical point of time for us to intervene and prevent cases at the very beginning."

He acknowledged that the Shenzhen effort was intense. "It's always a resource-intense requirement to do such extensive contact tracing, but that doesn't mean it shouldn't be done to the best of your ability to do so," he said.

He was struck by the low relative rate of infection among contacts in the study — around 7%. "There are differences obviously in infection rates in every outbreak," he said. "Every individual has their own particular infection rate. While we can take ranges and statistical guesses for every individual patient, it could be very high or very low, and that's most critical to nip it in the bud."

Lead author Qifang Bi and study coauthors had no financial relationships to disclose.

SOURCE: Bi Q et al. Lancet Infect Dis. 2020 Apr 27. doi: 10.1016/S1473-3099(20)30287-5.

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