Study population and setting
This study described a SARS-CoV-2 outbreak in a building with a call center in Seoul, South Korea between February 21 and March 8, 2020. All occupants of the building were offered testing, and those tested were followed up for 14 days for monitoring and subsequent testing. Household contacts were monitored, and cell phone data was used to identify individuals who stayed more than 5 minutes near the building. Notification messages were sent to these 16,628 identified individuals. The investigation included 1145 individuals including 922 employees in commercial offices, 203 residents who lived in the residential apartments, and 20 visitors of the building between February 21 and March 8, 2020. Cases were confirmed using evidence of SARS-CoV-2 RNA by RT-PCR and classified as symptomatic, pre-symptomatic, and asymptomatic at the time of testing, based on follow-up for 14 days following the first test.
Summary of Main Findings
The first known case in this cluster had a symptom onset date of February 22, 2020. The overall attack rate among the 1143 individuals tested within the building was estimated to be 8.5% (95% CI 7.0–10.3). 96.9% of the total confirmed cases in the building were employees of the call center on the 11th floor, almost all of whom were on the same side of the office space. The attack rate on the 11th floor was 43.5% (95% CI 36.9%–50.4%). This extensive investigation to identify transmission shows that it was limited to co-workers who worked in close proximity to one another, and there was no identified transmission among people who shared elevators, or common areas with these workers. Among the 97 confirmed cases 91.7% were symptomatic, 4.1% were pre-symptomatic, and 4.1% were asymptomatic. The secondary attack rate among households of symptomatic cases was 16.2% (95% CI 11.6%– 22.0%).
This study included a 14 day follow up of both cases and their close contacts to identify transmission events and describe the proportion with asymptomatic infections Additionally, this study describes the implementation of contact tracing methods to limit spread through quarantine and case isolation.
Not all clinical information was available for the confirmed cases.
This study describes an outbreak and high attack rate within a high-density work environment, which contributes to the understanding of risk within enclosed offices where people work in close proximity. Additionally, the risk to those who shared common spaces, such as elevators and lobby areas, was very low. Sixteen percent of household contacts of symptomatic cases were infected.
This review was posted on: 10 July 2020