Contact Tracing during COVID-19 outbreak, South Korea

Contact Tracing during COVID-19 outbreak, South Korea. Spencer EA, Heneghan C.

Published on August 20, 2020

Reference Park YJ, Choe YJ, Park O, et al. Contact Tracing during Coronavirus Disease Outbreak, South Korea, 2020 [published online ahead of print, 2020 Jul 16]. Emerg Infect Dis. 2020;26(10):10.3201/eid2610.201315. 2020
Study type
Country S Korea
Setting Contract tracing, household and non-household contacts
Funding Details
Transmission mode
Exposures Household and non-household contacts

Bottom Line

During lockdown in South Korea, positive PCR-test cases of COVID-19 were identified among 12% of household contacts and 1.9% of non-household contacts.

Evidence Summary

High-risk contacts (household & healthcare staff) were routinely tested

  • 5,706 positive PCR-tested cases were identified as index cases:
  • 59,073 contacts of these cases were identified: 10,592 household, 48,481 non-household

Non-high risk contacts were tested only if symptomatic

  • Contacts were monitored for an average of 9.9 (8.2 to 12.5) days after index case identification
  • Within the follow-up period, 11.8% (95%CI 11.2 to 12.4)% household contacts tested positive; non-household contacts 1.9 (1.8 to 2.0)% tested positive. Symptomatology was not reported.

What did they do?

This was a study of the transmission of COVID-19, using data from the contact tracing of confirmed cases (confirmed by RT-PCR) in South Korea. 

This study was conducted in the middle of a lockdown period in S Korea. Schools were closed and households largely stayed home except for essential tasks. The authors compared numbers of detected cases among household and non-household contacts, and within ten year age groups. Symptomatology was not reported.

Study reliability

NB: Although this study has been reported as giving data to compare transmission among children of different age groups, it was not designed or powered to make such a comparison. In addition, the context was not in schools, so should not be interpreted to understand risk in schools.

The study had no published protocol, and although moderately large in this context, looking at the subgroups by age brings the numbers to an unreliable level.

Direction of transmission could not be established although the assumption is that the index case passes it to subsequently identified cases.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes Yes Unclear Yes No

What else should I consider?

This study has been cited in the media as the basis for believing that younger children posed low risks of transmission but that children of secondary school age were likely to transmit at rates similar to adults. 

Household transmission was higher than non-household: NB the testing strategies were different for these two groups, and the study was conducted during lockdown when all stayed at home except for essential tasks.

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Elizabeth Spencer

Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.