Background: Patients with coronavirus disease 2019 (COVID-19) can unknowingly spread the virus to several people during the early subclinical period. Methods: We evaluated the viral dynamics in various body fluid specimens, such as nasopharyngeal swab, oropharyngeal swab, saliva, sputum, and urine specimens, of two patients with COVID-19 from hospital day 1 to 9. Additional samples of the saliva were taken at 1 hour, 2 hours, and 4 hours after using a chlorhexidine mouthwash. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load was determined by real-time reverse transcriptase polymerase chain reaction (rRT-PCR). Results: SARS-CoV-2 was detected from all the five specimens of both patients by rRT-PCR. The viral load was the highest in the nasopharynx (patient 1 = 8.41 log 10 copies/mL; patient 2 = 7.49 log 10 copies/mL), but it was also remarkably high in the saliva (patient 1 = 6.63 log 10 copies/mL; patient 2 = 7.10 log 10 copies/mL). SARS-CoV-2 was detected up to hospital day 6 (illness day 9 for patient 2) from the saliva of both patients. The viral load in the saliva decreased transiently for 2 hours after using the chlorhexidine mouthwash. Conclusion: SARS-CoV-2 viral load was consistently high in the saliva; it was relatively higher than that in the oropharynx during the early stage of COVID-19. Chlorhexidine mouthwash was effective in reducing the SARS-CoV-2 viral load in the saliva for a short-term period.

Objectives We aimed to compare epidemiologic features of second and third COVID-19 pandemic waves in South Korea. Methods Nationwide COVID-19 data was collected during the study period (May 6–December 30). The degree of social activities was also estimated using the internet searching trend analysis program for leisure-related keywords including “eating-out,” “trip,” and “get directions” (transportation). We compared the demographics, transmission chains, case fatality rates, social activity level, and public health responses between second (August 13–September 18) and third (November 4–present) waves. Results Compared to the second wave, the third wave was characterized by delayed social distancing reinforcement (3 vs. 15 days), longer duration (36 vs. > 56 days) and higher fatality rates (0.91% vs. 1.26%). There was a significant difference in transmission chains of the second and third waves of the COVID-19 pandemic (p < 0.01). During the third wave compared with the second wave, the proportion of local clusters (24.8% vs. 45.7%) was lower, while those of personal contact transmission (38.5% vs. 25.9%) and unknown routes of transmission (23.5% vs. 20.8%) were higher. Conclusion Early and timely interventions with strengthened social distancing policies should be implemented to effectively suppress and control the COVID-19 pandemic.

Asymptomatic infection and atypical manifestations of COVID-19: Comparison of viral shedding duration Dear Editor, Coronavirus disease 2019 (COVID-19) bears several challenging problems, including insidious symptom onset, subclinical manifestations and highly transmissible property during early stage of infection. 1 In the recent study by Huang et al., SARS-CoV-2infection presented strong infectivity during the incubation period with rapid transmission. 2 Some patients with COVID-19 are asymptomatic, while others complain of atypical symptoms including loss of smell and taste sense. 3 However, there is insufficient data on the prevalence of asymptomatic infection and atypical manifestations of COVID-19. In this study, we aimed to evaluate the prevalence of asymptomatic infection, anosmia (smell loss) and ageusia (taste loss) among patients with mild COVID-19 in a residential treatment center (RTC). We also compared the duration of SARS-CoV-2 viral shedding between groups with different clinical manifestations. An observational cohort study was conducted for 199 patients with COVID-19 in a RTC at Gyeongju, Gyeongsangbuk province, Republic of Korea (ROK). The RTC was introduced to care patients with mild COVID-19 for the efficient distribution of limited medical resources during large epidemic in early March 2020. Data on demographic findings, symptoms, and duration of viral shedding were collected. The patients were interviewed about initial symptoms and their duration in detail. Real-time PCR (RT-PCR) to detect SARS-CoV-2 was performed every 2-7 days. Duration of viral shedding was considered as time from diagnosis date to the day before first negative conversion of two consecutive negative results of RT-PCR. RT-PCR was conducted using Allplex 2019-nCoV assay (Seegene, Seoul, South Korea). Statistical analyses were performed using SPSS 20.0 program. Mann-Whitney U test was performed to compare the duration of viral shedding between groups with different clinical manifestations. P-value < 0.05 was considered statistically significant. This study was approved by the Institutional Review Board of Korea University Guro Hospital (approval number: 2020GR0135). Among 199 patients with COVID-19, male was 34.7% and mean age of the patients was 38.0 years (Table 1). Most patients (187, 94.0%) were healthy without chronic medical conditions. Among 199 patients, 26.6% were asymptomatic. In the early study, asymptomatic cases accounted for 10.7% (3/28) of COVID-19 cases in the ROK. 1 Asymptomatic proportion of COVID-19 was estimated as 17.9% (95% credible interval, 15.5-20.2%) on the Diamond Princess cruise ship, Japan. 4 Among clinical manifestations, cough (41.2%) was most common, followed by rhinorrhea and nasal stuffiness (30.2%). Of note, 26.1% (52/199) of patients presented anosmia, and 22.6% (45/199) complained of ageusia. Thirty-eight (19.1%) patients complained of both anosmia and ageusia. Duration of anosmia and

Social distancing has been adopted as one of basic protective measures against coronavirus disease 2019 (COVID-19). During 2019-2020 season, influenza epidemic period was exceptionally short and epidemic peak was low in comparison with previous seasons in Korea. Influenza epidemic pattern was bimodal in 2016-2017 and 2018-2019 seasons, however, influenza viruses have rarely been circulating in spring, 2020 in Korea. Although multiple factors could affect the size of influenza epidemic, extensive application of nonpharmaceutical interventions including mask wearing and social distancing in response to COVID-19 seems to be a major factor of reduced influenza epidemic. Social distancing measures with high feasibility and high acceptability should be implemented even if severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are developed in the future. Establishment of guideline for workplace social distancing is needed and it would contribute to reduce disease burden of influenza, especially in vaccine mismatch year.

Serosurveillance studies reveal the actual disease burden and herd immunity level in the population. In Seoul, Korea, a cross-sectional investigation showed 0.07% anti-severe acute respiratory syndrome coronavirus-2 antibody seropositivity among 1,500 outpatients of the university hospitals. Low seroprevalence reflects well-implemented social distancing. Serosurveillance should be repeated as the pandemic progresses.