E ffective contact tracing is critical to controlling the spread of coronavirus disease (COVID-19) (1). South Korea adopted a rigorous contact-tracing program comprising traditional shoe-leather epidemiology and new methods to track contacts by linking large databases (global positioning system, credit card transactions, and closed-circuit television). We describe a nationwide COVID-19 contact tracing program in South Korea to guide evidence-based policy to mitigate the pandemic (2). The Study South Korea's public health system comprises a national-level governance (Korea Centers for Disease Control and Prevention), 17 regional governments, and 254 local public health centers. The first case of COVID-19 was identified on January 20, 2020; by May 13, a total of 10,962 cases had been reported.

We describe the epidemiology of a coronavirus disease (COVID-19) outbreak in a call center in South Korea. We obtained information on demographic characteristics by using standardized epidemiologic investigation forms. We performed descriptive analyses and reported the results as frequencies and proportions for categoric variables. Of 1,143 persons who were tested for COVID-19, a total of 97 (8.5%, 95% CI 7.0%–10.3%) had confirmed cases. Of these, 94 were working in an 11th-floor call center with 216 employees, translating to an attack rate of 43.5% (95% CI 36.9%–50.4%). The household secondary attack rate among symptomatic case-patients was 16.2% (95% CI 11.6%– 22.0%). Of the 97 persons with confirmed COVID-19, only 4 (1.9%) remained asymptomatic within 14 days of quarantine, and none of their household contacts acquired secondary infections. Extensive contact tracing, testing all contacts, and early quarantine blocked further transmission and might be effective for containing rapid outbreaks in crowded work settings.

IMPORTANCE There is limited information describing the full spectrum of coronavirus disease 2019 (COVID-19) and the duration of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA detection in children. OBJECTIVE To analyze the full clinical course and the duration of SARS-CoV-2 RNA detectability in children confirmed with COVID-19 in the Republic of Korea, where rigorous public health interventions have been implemented. DESIGN, SETTING, AND PARTICIPANTS This case series of children with COVID-19 was conducted in 20 hospitals and 2 nonhospital isolation facilities across the country from February 18, 2020, to March 31, 2020. Children younger than 19 years who had COVID-19 were included. EXPOSURES Confirmed COVID-19, detected via SARS-CoV-2 RNA in a combined nasopharyngeal and oropharyngeal swab or sputum by real-time reverse transcriptionpolymerase chain reaction. MAIN OUTCOMES AND MEASURES Clinical manifestations during the observation period, including the time and duration of symptom occurrence. The duration of SARS-CoV-2 RNA detection was also analyzed. RESULTS A total of 91 children with COVID-19 were included (median [range] age, 11 [0-18] years; 53 boys [58%]). Twenty children (22%) were asymptomatic during the entire observation period. Among 71 symptomatic cases, 47 children (66%) had unrecognized symptoms before diagnosis, 18 (25%) developed symptoms after diagnosis, and only 6 (9%) were diagnosed at the time of symptom onset. Twenty-two children (24%) had lower respiratory tract infections. The mean (SD) duration of the presence of SARS-CoV-2 RNA in upper respiratory samples was 17.6 (6.7) days. Virus RNA was detected for a mean (SD) of 14.1 (7.7) days in asymptomatic individuals. There was no difference in the duration of virus RNA detection between children with upper respiratory tract infections and lower respiratory tract infections (mean [SD], 18.7 [5.8] days vs 19.9 [5.6] days; P = .54). Fourteen children (15%) were treated with lopinavir-ritonavir and/or hydroxychloroquine. All recovered, without any fatal cases. CONCLUSIONS AND RELEVANCE In this case series study, inapparent infections in children may have been associated with silent COVID-19 transmission in the community. Heightened surveillance using laboratory screening will allow detection in children with unrecognized SARS-CoV-2 infection.

ObjectiveTransmissibility of COVID-19 by children in the household is not clear. Herein, we describe children’s role in household transmission of COVID-19.Design and settingAll paediatric COVID-19 index cases and their household members reported from 20 January to 6 April 2020 in South Korea were reviewed. The secondary attack rate (SAR) from child index case to household secondary case was calculated. Epidemiological and clinical findings of child index case-household secondary case pair was assessed.ResultsA total of 107 paediatric COVID-19 index cases and 248 of their household members were identified. One pair of paediatric index-secondary household case was identified, giving a household SAR of 0.5% (95% CI 0.0% to 2.6%). The index case was self-quarantined at home after international travel, stayed in her room, but shared a meal table with the secondary case.ConclusionThe SAR from children to household members was low in the setting of social distancing, underscoring the importance of rigorous contact tracing and early isolation in limiting transmission within households.

Background We hypothesized that nationwide social distancing and other preventive measures for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were associated with reduced detection of other respiratory viruses in South Korea. Methods We analyzed national surveillance data to compare incidence of respiratory viruses during 2016–2019 vs 2020. Results of multiplex reverse-transcription polymerase chain reaction assays for 8 respiratory viruses were included: adenovirus (ADV), parainfluenza virus (PIV), respiratory syncytial virus (RSV), influenza virus (IFV), human coronavirus (HCoV; non–SARS-CoV-2), human rhinovirus (HRV), human bocavirus (HBoV), and human metapneumovirus (HMPV). Results During 2016–2019, rates of detection of respiratory viruses were relatively stable: ADV, 3.7%–9.2%; PIV, 1.4%–17.0%; RSV, 0.3%–15.3%; IFV, 0.4%–35.6%; HCoV, 1.5%–8.4%; HRV, 7.0%–25.1%; HBoV, 0.6%–6.3%; and HMPV, 0.7%–14.5%. Following implementation of social distancing in February 2020, rates of detection of enveloped viruses (HCoV, HMPV, IFV, PIV, and RSV) were significantly reduced by up to 100%. However, nonenveloped viruses (ADV, HRV, and HBoV) persisted throughout 2020, and HRV rates in hospitalized patients significantly increased. Conclusions After implementation of social distancing for SARS-CoV-2 in South Korea, rates of detection of enveloped respiratory viruses decreased significantly, whereas nonenveloped viruses persisted, suggesting that enhanced infection prevention strategies are required to mitigate spread of these viruses.