key: cord-1024116-rvz9afqo
authors: Jung, Chan-Young; Park, Haeyong; Kim, Dong Wook; Choi, Yoon Jung; Kim, Seong Woo; Chang, Tae Ik
title: Clinical Characteristics of Asymptomatic Patients with COVID-19: A Nationwide Cohort Study in South Korea
date: 2020-08-06
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2020.08.001
sha: f931408543e997b067351b12ff09bd67ec47d6d8
doc_id: 1024116
cord_uid: rvz9afqo

OBJECTIVES: To delineate clinical characteristics of asymptomatic and symptomatic patients confirmed with COVID-19 in South Korea. METHODS: Data were obtained from the Korean National Health Insurance Service database linked to the Korea Centers for Disease Control and Prevention data. RESULTS: Among 10,237 patients (mean [SD] age, 45.0 [19.8] years; 60.1% female) who met the eligibility criteria for the study, 6,350 (62.0%) patients were asymptomatic, and 3,887(38.0%) patients were symptomatic. The mean and median age was similar between asymptomatic and symptomatic patients. Notably, we observed a U-shaped association between age group and the proportion of asymptomatic patients, with the nadir at 57.3% in the 40-49 age group. This U-shaped distribution was largely similar between men and women. The overall prevalence of asymptomatic individuals was higher, regardless of sex, residential area, income levels, and comorbid conditions. CONCLUSIONS: In this national cohort of over 10,000 patients with COVID-19, more than 60% of all cases in South Korea reported no symptoms at the time of diagnosis. Expanding criteria for contact tracing and testing to capture potential transmission before symptom onset should be urgently considered to inform control strategies for COVID-19.

 Our findings suggest that a significant proportion of confirmed COVID-19 cases are asymptomatic at the time of confirmation, and therefore, symptom-based screening alone may fail to control transmission during the infected but asymptomatic stage.

 Expanding criteria for contact tracing and testing should be urgently considered.

J o u r n a l P r e -p r o o f

In South Korea, the first coronavirus disease 2019 (COVID-19) case was confirmed on January 20, 2020. 1 With proactive containment efforts, comprehensive contact tracing, and extensive testing of symptomatic or high risk individuals for COVID-19, South Korea was able to flatten the curve of new COVID-19 infections by mid-March. 1, 2 However, studies of various sub-populations have raised important concerns regarding possible transmission of the virus by asymptomatic or presymptomatic infected persons. [2] [3] [4] Hence, to better inform the global medical community during the current worldwide pandemic, we sought to delineate the clinical characteristics of asymptomatic and symptomatic patients in a national cohort comprised of over 10,000 patients confirmed with COVID-19 from the Korean National Health Insurance Service (NHIS) database linked to Korea Centers for Disease Control and Prevention (KCDC) data.

The cohort included all patients confirmed with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections by a positive result on polymerase chain reaction test of a nasopharyngeal or oropharyngeal sample between January 24, 2020 and April 9, 2020, in South Korea. After excluding 207 patients who were not enrolled in the 2015-2019 NHIS database (e.g., foreigners or long-term foreign residents), a total of 10,237 patients were included in the final analysis. We characterized patients by socio-demographics, comorbid conditions, and presence/absence of symptoms. Information on presenting symptoms was collected by telephone interviews within the first 24 hours following a positive test for SARS-CoV-2 as part of contact tracing. Comorbidities were assessed using the International Classification of Disease, Tenth Revision, which were ascertained by the presence of at least J o u r n a l P r e -p r o o f two or more diagnostic codes identified up to five years prior to diagnosis of COVID-19. The Charlson comorbidity index score was also calculated as a proxy of disease burden and illness severity. 5 Data from descriptive analyses were summarized using means (standard deviations, SD), medians (inter-quartile range), or proportions. The Institutional Review Board of the NHIS Ilsan Hospital approved this study and waived the requirement for informed consent as only deidentified data were examined.

As of May 28 July 23, 2020, South Korea had confirmed 13,938 11,344 cases (including 2,145 1,232 imported cases) of SARS-CoV-2 infection. 1 (table 1) . The mean and median age was similar between asymptomatic and symptomatic patients. Notably, we observed a U-shaped association between age group and the proportion of asymptomatic patients, with the nadir at 57.3% in the 40-49 age group. This U-shaped distribution was largely similar between men and women ( Figure 1 ). The overall prevalence of asymptomatic individuals was higher, regardless of sex, residential area, income levels, and comorbid conditions.

Despite deployment of aggressive public health measures, COVID-19 has infected more than ten fifteen million people and continues to spread rapidly around the world. 1 A major challenge to containing the spread of COVID-19 is that asymptomatic people are also infectious, with proportions of these asymptomatic cases as high as 80%, depending on different clinical contexts. 6 where half of the patients eventually showed symptoms within the 14-day quarantine period, and only 4 case-patients remained asymptomatic even after 14 days of isolation. 8 Hence, it is important to note that detailed information including chronological follow-up of symptoms is essential in differentiating "asymptomatic" from "pre-symptomatic" patients. 9 In this national cohort of over 10,000 patients with COVID-19, more than 60% of all cases in South Korea reported no symptoms at the time of diagnosis. While it is uncertain whether these patients eventually went on to develop symptoms, our findings suggest again highlight that a significant proportion of confirmed COVID-19 cases are asymptomatic at the time of testing, and therefore, symptom-based screening alone may fail to control transmission during the infected but asymptomatic stage. Expanding criteria for contact tracing and testing to capture potential transmission before symptom onset should be urgently considered to inform control strategies for COVID-19. Definition of abbreviations: SD = standard deviation; IQR = inter-quartile range; CCI = Charlson comorbidity index.

Center for Disease Control and Prevention. The updates on COVID-19 in Korea: for press release. 2020. Available from

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