dcyphr | Contact Tracing during Coronavirus Disease Outbreak, South Korea, 2020


This paper covers findings from South Korea’s nationwide contact tracing efforts. These efforts were carried out to monitor and slow COVID-19 infections in the country. The authors analyze reports from the contact tracing and come up with infection statistics for people who got infected at home and for people who got infected elsewhere.


Contact tracing is important for slowing the spread of COVID-19. South Korea has kept track of who has come into contact with whom by looking at GPS locations, credit card purchases, and CCTV footage, as well as by using other traditional contact tracing methods.

The Study

The first confirmed COVID-19 case was reported on January 20th, 2020. Between then and May 13th of the same year, 10,962 total cases were reported.

For the purposes of this study, the authors define an “index patient” as a person with the first known COVID-19 case in their local area. Index patients were grouped by age. The authors also define two types of COVID-19 contacts. “Household” contacts are people who have come into contact with an infected person living in their household. “Non Household” contacts refer to everyone else.

The authors monitored 59,073 people who were known to have been in contact with at least one person infected with COVID-19. Contacts were typically monitored for a bit over a week, and the number of contacts who eventually contracted COVID-19 were recorded. The age and type (household / non household) of all contacts who were later infected were also kept track of.


Index patients who were 40 years old or older spread COVID-19 to their contacts at a greater rate than other age groups. Household contacts contracted COVID-19 more frequently than non household contacts, with a total of 11.8% being infected as opposed to only 1.9% of non household contacts. These numbers may show a possible need for mask-wearing and social distancing to be carried out at home. 

The index patients who transmitted COVID-19 to household contacts at the highest rate were children old enough to attend school. The index patients who transmitted COVID-19 to household contacts at the lowest rate were children whose schools were closed. This reaffirms the importance of closing schools to stop the spread of COVID-19.

The findings of this study are limited by the fact that household contacts and non household contacts were tested at different frequencies. Also, the authors could not feasibly include non-symptomatic patients in the study. However, the sample size of the study was large enough that the results deserve some attention.

This study reinforces the importance of contact tracing and social distancing measures. The authors call for future studies to look into how factors such as hygiene or at-home masking can limit household spread of the virus.