Rates of COVID-19 Infection Among Healthcare Workers in Designated COVID-19 Wards and General Wards

BackgroundTo evaluate the effects of isolating coronavirus disease 2019 (COVID-19) patients in general wards, we compared the rates of COVID-19 infection in nurses and nursing assistants working in COVID-19 designated wards and in general wards of our hospital from 1 October 2021 to 21 April 2022.MethodsThis study was conducted in a 2,700-bed tertiary care hospital in Seoul, Korea. Designated wards comprised single, negative pressure rooms and a 100% outdoor air system.ResultsDuring the study period, a total of 2,698 nurses and nursing assistants were employed at our hospital, of whom 310 (11%) were working in the designated wards, and the remaining 2,388 (89%) in the general wards, and among whom 1,158 (43%) were diagnosed with COVID-19. The healthcare workers (HCWs) in the designated wards were less frequently diagnosed with COVID-19 than those in the general wards (31% vs. 45%, P < 0.001). During the period before patients with COVID-19 were isolated in general wards, and during the period after these cases were isolated in general ward, HCWs in designated wards were less frequently infected with the virus than those in general wards (7% vs. 11%, P = 0.039; and 23% vs. 33%, P < 0.001, respectively).ConclusionHCWs in designated wards have a lower rate of contracting COVID-19 than those in general wards. A lack of exposure to undiagnosed cases and their caregivers, greater care with social distancing outside the hospital, higher rates of 3-dose vaccinations, and the use of isolation rooms with negative pressure may be associated with this finding.     

Strong SARS-CoV-2 Antibody Response After Booster Dose of BNT162b2 mRNA Vaccines in Uninfected Healthcare Workers

Despite strict guidelines for coronavirus disease 2019 (COVID-19), South Korea is facing its fourth pandemic wave. In this study, by using an automated electrochemiluminescence immunoassay assay, we tracked anti-spike protein receptor-binding domain (anti-S-RBD) antibody titer from the second dose to 2 weeks after the booster dose vaccination. After the second dose, 234 participants had their anti-S-RBD antibody titers decrease over time. We also showed the booster dose (the third dose) increased antibody titer by average 14 (min–max, 2–255)-fold higher compared to the second dose among the 211-booster group participants, therefore, the booster dose could be recommended for low responders to the second dose. Our findings showed a distinct humoral response after booster doses of BNT162b2 mRNA vaccines and may provide further evidence of booster vaccination efficacy. These data will also be helpful in vaccination policy decisions that determine the need for the booster dose.     

Prevalence of SARS-CoV-2 Antibody in 2,935 Healthcare Workers at 6 Major Hospitals,Daegu, Korea

BackgroundIn Korea, the first community outbreak of coronavirus disease 2019 (COVID-19) occurred in Daegu on February 18, 2020. This study was performed to investigate the prevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antibodies in healthcare workers (HCWs) at 6 major hospitals in Daegu.MethodsBlood specimens of 2,935 HCWs at 6 major hospitals in Daegu from January 2021 to February 2021 were collected. Every specimen was tested for antibody against SARS-CoV-2 using both Elecsys Anti-SARS-CoV-2 electrochemiluminescence immunoassay (Roche Diagnostics, Rotkreuz, Switzerland) and R-FIND COVID-19 IgG/M/A enzyme-linked immunosorbent assay kit (SG medical Inc., Seoul, Korea) as screening tests. If 1 or more of these screening test results was positive, 2 additional antibody tests were performed using Abbott Anti-SARS-CoV-2 IgG assay (Abbott, Abbott Park, IL, USA) and cPass SARS-CoV-2 Neutralization Antibody Detection Kit (GenScript USA Inc., Piscataway, NJ, USA). If 2 or more of the total 4 test results were positive, it was determined as positive for the antibody against SARS-CoV-2.ResultsAccording to the criteria of SARS-CoV-2 antibody positivity determination, 12 subjects were determined as positive. The overall positive rate of the SARS-CoV-2 antibody was 0.41% (12/2,935). Of the 12 subjects determined as positive, 7 were diagnosed with COVID-19, and the remaining 5 were nondiagnosed cases of COVID-19.ConclusionIn early 2021, the overall seroprevalence of SARS-CoV-2 antibody among HCW located in Daegu was 0.41%, and 0.17% excluding COVID-19 confirmed subjects. These results were not particularly high compared with the general public and were much lower than HCWs in other countries.     

Transmission of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) from pre and asymptomatic infected individuals: a systematic review

BackgroundThe role of SARS-Cov-2-infected persons who develop symptoms after testing (presymptomatics) or not at all (asymptomatics) in the pandemic spread is unknown.ObjectivesTo determine infectiousness and probable contribution of asymptomatic persons (at the time of testing) to pandemic SARS-CoV-2 spread.Data sourcesLitCovid, medRxiv, Google Scholar, and WHO Covid-19 databases (to 31 March 2021) and references in included studies.Study eligibility criteriaStudies with a proven or hypothesized transmission chain based either on serial PCR cycle threshold readings and/or viral culture and/or gene sequencing, with adequate follow-up.ParticipantsPeople exposed to SARS-CoV-2 within 2–14 days to index asymptomatic (at time of observation) infected individuals.InterventionsReliability of symptom and signs was assessed within contemporary knowledge; transmission likelihood was assessed using adapted causality criteria.MethodsSystematic review. We contacted all included studies' corresponding authors requesting further details.ResultsWe included 18 studies from a diverse setting with substantial methodological variation (this field lacks standardized methodology). At initial testing, prevalence of asymptomatic cases was 12.5–100%. Of these, 6–100% were later determined to be presymptomatic, this proportion varying according to setting, methods of case ascertainment and population. Nursing/care home facilities reported high rates of presymptomatic: 50–100% (n = 3 studies). Fourteen studies were classified as high risk of, and four studies as at moderate risk of symptom ascertainment bias. High-risk studies may be less likely to distinguish between presymptomatic and asymptomatic cases. Six asymptomatic studies and four presymptomatic studies reported culturing infectious virus; data were too sparse to determine infectiousness duration. Three studies provided evidence of possible and three of probable/likely asymptomatic transmission; five studies provided possible and two probable/likely presymptomatic SARS-CoV-2 transmission.ConclusionHigh-quality studies provide probable evidence of SARS-CoV-2 transmission from presymptomatic and asymptomatic individuals, with highly variable estimated transmission rates.     

Human Type II Taste Cells Express Angiotensin-Converting Enzyme 2 and Are Infected by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Chemosensory changes are well-reported symptoms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The virus targets cells for entry by binding of its spike protein to cell-surface angiotensin-converting enzyme 2 (ACE2). It is not known whether ACE2 is expressed on taste receptor cells (TRCs), or whether TRCs are infected directly. in situ hybridization probe and an antibody specific to ACE2 indicated presence of ACE2 on a subpopulation of TRCs (namely, type II cells in taste buds in taste papillae). Fungiform papillae of a SARS-CoV-2⁺ patient exhibiting symptoms of coronavirus disease 2019 (COVID-19), including taste changes, were biopsied. Presence of replicating SARS-CoV-2 in type II cells was verified by in situ hybridization. Therefore, taste type II cells provide a potential portal for viral entry that predicts vulnerabilities to SARS-CoV-2 in the oral cavity. The continuity and cell turnover of a patient''s fungiform papillae taste stem cell layer were disrupted during infection and had not completely recovered 6 weeks after symptom onset. Another patient experiencing post–COVID-19 taste disturbances also had disrupted stem cells. These results demonstrate the possibility that novel and sudden taste changes, frequently reported in COVID-19, may be the result of direct infection of taste papillae by SARS-CoV-2. This may result in impaired taste receptor stem cell activity and suggest that further work is needed to understand the acute and postacute dynamics of viral kinetics in the human taste bud.     

Vaccine Effect on Household Transmission of Omicron and Delta SARS-CoV-2 Variants

BackgroundWe evaluated the household secondary attack rate (SAR) of the omicron and delta severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, according to the vaccination status of the index case and household contacts; further, in vaccinated index cases, we evaluated the effect of the antibody levels on household transmission.MethodsA prospective cross-sectional study of 92 index cases and 197 quarantined household contacts was performed. Tests for SARS-CoV-2 variant type and antibody level were conducted in index cases, and results of polymerase chain reaction tests (during the quarantine period) were collected from contacts. Association of antibody levels in vaccinated index cases and SAR was evaluated by multivariate regression analysis.ResultsThe SAR was higher in households exposed to omicron variant (42%) than in those exposed to delta variant (27%) (P = 0.040). SAR was 35% and 23% for unvaccinated and vaccinated delta variant exposed contacts, respectively. SAR was 44% and 41% for unvaccinated and vaccinated omicron exposed contacts, respectively. Booster dose immunisation of contacts or vaccination of index cases reduced SAR of vaccinated omicron variant exposed contacts. In a model with adjustment, anti-receptor-binding domain antibody levels in vaccinated index cases were inversely correlated with household transmission of both delta and omicron variants. Neutralising antibody levels had a similar relationship.ConclusionImmunisation of household members may help to mitigate the current pandemic.     

Relative Effectiveness of COVID-19 Vaccination in Healthcare Workers: 3-Dose Versus 2-Dose Vaccination

The omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is known to have high infectivity and is more likely to evade vaccine immunity. However, booster vaccination is expected to strengthen cross-reactive immunity, thereby increasing the vaccine effectiveness (VE). This study aimed to evaluate the relative VE of the 3-dose (booster) vaccination compared with the 2-dose primary series vaccination in healthcare workers during omicron variant-dominant periods. During the omicron-dominant period from February 1, 2022 to February 28, 2022, a 1:1 matched case-control study was conducted. Healthcare workers with positive SARS-CoV-2 test results were classified as positive cases, whereas those with negative results served as controls. Compared with the 2-dose primary series vaccination, booster vaccination with mRNA vaccine showed moderate VE (53.1%). However, in multivariate analysis including the time elapsed after vaccination, the significant VE disappeared, reflecting the impact of recent vaccination rather than the third dose itself.     

Evidence of Long-Distance Droplet Transmission of SARS-CoV-2 by Direct Air Flow in a Restaurant in Korea

BackgroundThe transmission mode of severe acute respiratory syndrome coronavirus 2 is primarily known as droplet transmission. However, a recent argument has emerged about the possibility of airborne transmission. On June 17, there was a coronavirus disease 2019 (COVID-19) outbreak in Korea associated with long distance droplet transmission.MethodsThe epidemiological investigation was implemented based on personal interviews and data collection on closed-circuit television images, and cell phone location data. The epidemic investigation support system developed by the Korea Disease Control and Prevention Agency was used for contact tracing. At the restaurant considered the site of exposure, air flow direction and velocity, distances between cases, and movement of visitors were investigated.ResultsA total of 3 cases were identified in this outbreak, and maximum air flow velocity of 1.2 m/s was measured between the infector and infectee in a restaurant equipped with ceiling-type air conditioners. The index case was infected at a 6.5 m away from the infector and 5 minutes exposure without any direct or indirect contact.ConclusionDroplet transmission can occur at a distance greater than 2 m if there is direct air flow from an infected person. Therefore, updated guidelines involving prevention, contact tracing, and quarantine for COVID-19 are required for control of this highly contagious disease.     

How COVID-19 Affected Healthcare Workers in the Hospital Locked Down due to Early COVID-19 Cases in Korea

BackgroundThe healthcare workers (HCWs) were exposed to never-experienced psychological distress during the early stage of the coronavirus disease 2019 (COVID-19) pandemic. The aim of this study was to investigate how the COVID-19 pandemic affected the mental health of HCWs during the hospital lockdown period due to mass healthcare-associated infection during the early spread of COVID-19.MethodsA real-time online survey was conducted between April 14–18, 2020 among HCWs who worked at the university hospital where COVID-19 was confirmed in a patient, and the hospital was shut down for 3 weeks. Along with demographic variables and work-related information, psychological distress was measured using the Generalized Anxiety Disorder-7 (GAD-7), the Patient Health Questionnaire-9 (PHQ-9), the Maslach Burnout Inventory-General Survey scale, and the Stress and Anxiety to Viral Epidemics-9.ResultsThe HCWs working in the cohort ward and those who have experienced social discrimination had significantly higher level of depression (PHQ-9 score; 5.24 ± 4.48 vs. 4.15 ± 4.38; P < 0.01 and 5.89 ± 4.78 vs. 3.25 ± 3.77; P < 0.001, respectively) and anxiety (GAD-7 score; 3.69 ± 3.68 vs. 2.87 ± 3.73; P < 0.05 and 4.20 ± 4.22 vs. 2.17 ± 3.06; P < 0.001, respectively) compared to other HCWs. Worries regarding the peer relationship and the skepticism about job were associated with depression (odds ratio [OR], 1.39; 95% confidence interval [CI], 1.07–1.79; P < 0.05 and OR, 1.69; 95% CI, 1.31–2.17; P < 0.001, respectively) and anxiety (OR, 1.73; 95% CI, 1.21–2.49; P < 0.01 and OR, 1.54; 95% CI, 1.09–2.17; P < 0.05, respectively), while fear of infection or worsening of health was not. Path analysis showed that work-related stress associated with the viral epidemic rather than anxiety about the viral epidemic mainly contributed to depression.ConclusionThe present observational study indicates that mental health problems of HCWs exposed to COVID-19 are associated with distress in work and social relationship. Early intervention programs focusing on these factors are necessary.     

Genomic Evolution of Severe Acute Respiratory Syndrome Coronavirus 2 in India and Vaccine Impact

Recent emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and subsequent containment procedures have impacted the world as never seen before. Therefore, there is considerable curiosity about the genome evolution related to the origin, transmission and vaccine impact of this virus. We have analysed genome sequences of SARS-CoV-2 isolated from Indian patients to gain an in-depth understanding of genomic evolution and transmission in India. Phylogenetic analysis and mutation profiling revealed major lineages being evolved by characteristic mutations. As the mutation frequency in spike protein is comparatively lesser, the candidate vaccines expected to have wide coverage worldwide including India.     

Evidence of increasing diversification of emerging Severe Acute Respiratory Syndrome Coronavirus 2 strains

On 30th January 2020, an outbreak of atypical pneumonia caused by a novel betacoronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was declared a public health emergency of international concern by the World Health Organization. For this reason, a detailed evolutionary analysis of SARS-CoV-2 strains currently circulating in different geographic regions of the world was performed. A compositional analysis as well as a Bayesian coalescent analysis of complete genome sequences of SARS-CoV-2 strains recently isolated in Europe, North America, South America, and Asia was performed. The results of these studies revealed a diversification of SARS-CoV-2 strains in three different genetic clades. Co-circulation of different clades in different countries, as well as different genetic lineages within different clades were observed. The time of the most recent common ancestor was established to be around 1st November 2019. A mean rate of evolution of 6.57 × 10⁻⁴ substitutions per site per year was found. A significant migration rate per genetic lineage per year from Europe to South America was also observed. The results of these studies revealed an increasing diversification of SARS-CoV-2 strains. High evolutionary rates and fast population growth characterizes the population dynamics of SARS-CoV-2 strains.     

Work Restrictions for Healthcare Personnel with Potential In-hospital Exposure to SARS-CoV-2: Experience at a Tertiary Hospital

Applying work restrictions for asymptomatic healthcare personnel (HCP) with potential exposure to coronavirus disease 2019 (COVID-19) is recommended to prevent transmission from potentially contagious HCP to patients and other HCP. However, it can lead to understaffing, which threatens the safety of both patients and HCP. We evaluated 203 COVID-19 exposure events at a single tertiary hospital from January 2020 to June 2021. A total of 2,365 HCP were potentially exposed, and work restrictions were imposed on 320 HCP, leading to the loss of 3,311 working days. However, only one of the work-restricted HCP was confirmed with COVID-19. During the study period, the work restriction measures might be taken excessively compared to their benefit, so establishing more effective standards for work restriction is required.     

Importation and Transmission of SARS-CoV-2 B.1.1.529 (Omicron) Variant of Concern in Korea,November 2021

In November 2021, 14 international travel-related severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.529 (omicron) variant of concern (VOC) patients were detected in South Korea. Epidemiologic investigation revealed community transmission of the omicron VOC. A total of 80 SARS-CoV-2 omicron VOC-positive patients were identified until December 10, 2021 and 66 of them reported no relation to the international travel. There may be more transmissions with this VOC in Korea than reported.     

Positivity of SARS-CoV-2 Antibodies among Korean Healthy Healthcare Workers 1 and 2 Weeks after Second Dose of Pfizer-BioNTech Vaccination

The antibody titer of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was observed in 289 healthy healthcare workers who had completed the second dose of the Pfizer-BioNTech coronavirus disease 2019 (COVID-19) vaccine. Antibody tests were performed using both the automated electrochemiluminescence immunoassay (ECLIA) and the chromatographic lateral flow immunoassay (LFIA). All subjects had antibodies against the receptor binding domain of the spike protein of SARS-CoV-2 only one week after completing the vaccination, and the antibody titer became significantly higher after another week (P < 0.001). Since there was a large amount of antibody formation within two weeks after completion of vaccination, the less sensitive method, LFIA, also showed high sensitivity. There was no significant difference between whole blood and serum in detecting SARS-CoV-2 antibodies after vaccination. This is an early study of vaccinations among Koreans and is expected to contribute to the establishment of national guidelines on COVID-19 vaccination.     

SARS-CoV-2 host diversity: An update of natural infections and experimental evidence

Coronavirus disease-19 (COVID-19) caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is now a pandemic threat. This virus is supposed to be spread by human to human transmission. Cellular angiotensin-converting enzyme 2 (ACE2) is the receptor of SARS-CoV-2 which is identical or similar in different species of animals such as pigs, ferrets, cats, orangutans, monkeys, and humans. Moreover, a recent study predicted that dogs might be secondary hosts during the evolution of SARS-CoV-2 from bat to human. Therefore, there is a possibility of spreading SARS-CoV-2 through domestic pets. There are now many reports of SARS-CoV-2 positive cases in dogs, cats, tigers, lion, and minks. Experimental data showed ferrets and cats are highly susceptible to SARS-CoV-2 as infected by virus inoculation and can transmit the virus directly or indirectly by droplets or airborne routes. Based on these natural infection reports and experimental data, whether the pets are responsible for SARS-CoV-2 spread to humans; needs to be deeply investigated. Humans showing clinical symptoms of respiratory infections have been undergoing for the COVID-19 diagnostic test but many infected people and few pets confirmed with SARS-CoV-2 remained asymptomatic. In this review, we summarize the natural cases of SARS-CoV-2 in animals with the latest researches conducted in this field. This review will be helpful to think insights of SARS-CoV-2 transmissions, spread, and demand for seroprevalence studies, especially in companion animals.     

Progression and Resolution of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection in Golden Syrian Hamsters

To catalyze severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) research, including development of novel interventive and preventive strategies, the progression of disease was characterized in a robust coronavirus disease 2019 (COVID-19) animal model. In this model, male and female golden Syrian hamsters were inoculated intranasally with SARS-CoV-2 USA-WA1/2020. Groups of inoculated and mock-inoculated uninfected control animals were euthanized at 2, 4, 7, 14, and 28 days after inoculation to track multiple clinical, pathology, virology, and immunology outcomes. SARS-CoV-2–inoculated animals consistently lost body weight during the first week of infection, had higher lung weights at terminal time points, and developed lung consolidation per histopathology and quantitative image analysis measurements. High levels of infectious virus and viral RNA were reliably present in the respiratory tract at days 2 and 4 after inoculation, corresponding with widespread necrosis and inflammation. At day 7, when the presence of infectious virus was rare, interstitial and alveolar macrophage infiltrates and marked reparative epithelial responses (type II hyperplasia) dominated in the lung. These lesions resolved over time, with only residual epithelial repair evident by day 28 after inoculation. The use of quantitative approaches to measure cellular and morphologic alterations in the lung provides valuable outcome measures for developing therapeutic and preventive interventions for COVID-19 using the hamster COVID-19 model.

In December 2019, a novel β coronavirus was isolated from patients who presented with severe and ultimately fatal pneumonia in Wuhan, China.¹ The virus was designated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and rapidly spread through human-to-human transmission, causing the current global pandemic of coronavirus disease 2019 (COVID-19). As of September 2021, there have been >218 million confirmed cases and >4.5 million deaths globally attributed to SARS-CoV-2 infection [World Health Organization: Coronavirus Disease (COVID-19) Pandemic, https://www.who.int/emergencies/diseases/novel-coronavirus-2019, last accessed September 2, 2021).Although many organ systems can be affected by SARS-CoV-2 infection, pulmonary disease has been most frequently associated with severe and fatal cases of COVID-19.² The earliest stage of disease is characterized by edema and vascular damage, including endothelial cell degeneration and necrosis, with neutrophilic infiltration of alveolar septa and capillaries (endothelialitis and capillaritis) and microthrombosis.2, 3, 4, 5 This is followed by an exudative phase of diffuse alveolar damage, with fibrinous edema in the alveolar spaces, increased numbers of macrophages and epithelial multinucleated giant cells, hyaline membrane formation, and epithelial necrosis, followed by type 2 pneumocyte hyperplasia. In addition, vascular changes occur, including endothelial necrosis, hemorrhage, thrombosis of capillaries and small arteries, and vasculitis.^4,6 In turn, the organizing stage of diffuse alveolar damage and the final fibrotic stage of diffuse alveolar damage ensue, which may include proliferation of myofibroblasts within the lung interstitium and deposition of collagen, leading to fibrosis. Squamous metaplasia has also been observed.^2,7The emergent and widespread nature of this pandemic necessitated the rapid development of multiple animal models and biological systems to study various aspects of pathogenesis, treatment, and prevention of disease. To date, reported animal models of COVID-19 pathology include human angiotensin-converting enzyme 2 transgenic mice,8, 9, 10, 11 golden Syrian hamsters,11, 12, 13, 14, 15, 16, 17 nonhuman primates,^18,19 and ferrets.^20,21 Recent comprehensive reviews of animal models of COVID-19 were provided by Zeiss et al²² and Veenhuis and Zeiss²³ in 2021. Each model species has advantages and limitations with respect to similarity to disease in humans, expense, and practicality. The hamster model offers several advantages over other animal models: it is a relatively small, immunocompetent animal that is susceptible to infection with varied SARS-CoV-2 clinical isolates and readily develops pulmonary disease. Specifically, hamsters consistently develop moderate to severe bronchointerstitial pneumonia characterized by acute inflammation, edema, and necrosis 2 to 4 days after SARS-CoV-2 challenge, progressing to proliferative interstitial pneumonia with type II pneumocyte hyperplasia by 7 days after challenge. Pulmonary lesions have been reported to resolve around 10 to 14 days after inoculation, with little to no evidence of residual damage.^12,17,19,24Although several studies have provided an overview of pulmonary pathology during acute infection, comprehensive longitudinal assessments of pulmonary pathology are lacking, including chronic time points. Likewise, there is a dearth of information integrating clinical, pathology, virology, and immunology findings or reporting systemic pathologic findings associated with SARS-CoV-2 infection in hamsters. Accordingly, the current study provides in-depth, longitudinal, pathologic characterization of multisystemic disease manifestation caused by SARS-CoV-2 infection in male and female golden Syrian hamsters. Furthermore, tissue damage and inflammatory responses were measured by digital image analysis using an open-source platform, QuPath.^25,26 The current results show that inoculating hamsters intranasally with SARS-CoV-2 reliably induces acute damage to the respiratory tract with initial viral replication, followed by a macrophage-dominant pulmonary immune response. In turn, a reparative phase follows, with abundant type II pneumocyte hyperplasia restoring the alveolar lining, mirroring SARS-CoV-2 infection in humans.     

Infectivity of Coronavirus Disease 2019: A Prospective Cohort Study in the Korean Metropolitan Area

BackgroundAlthough several characteristics of coronavirus disease 2019 (COVID-19), an ongoing pandemic disease, have been identified, data on the infectivity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are limited.MethodsThis prospective cohort study was conducted to analyze the infectivity of SARS-CoV-2 based on data of all patients diagnosed with COVID-19 confirmed using real-time polymerase chain reaction test from January to April 2020 in Gyeonggi-do, the largest province in Korea.ResultsOf the 502 patients, 298 consisting of 106 clusters with 5,909 contacts were included. Of these, 277 (93.0%) were symptomatic, and the most common symptoms were cough, fever, sputum, sore throat, and headache. A total of 94 patients (31.5%) had pneumonia, while 8 (2.7%) died during the follow-up period. The secondary attack rate (SAR) in the study population was 3.5% (204/5,909). In exposure settings, the SAR was higher in religious gathering (13.5% [95% confidence interval, 10.7–16.8%]), workplaces (8.49% [95% CI, 6.08–11.74%]), and schools (6.38% [95% CI, 3.39–11.69%]) than in health care facilities (1.92% [95% CI, 1.45–2.55%]). Sore throat at any period, dyspnea at diagnosis or any period, lower cycle threshold value in the lower respiratory tract samples, leukocytosis, and higher bilirubin levels were associated with higher infectivity of COVID-19. The presence of symptoms was not related to the infectivity.ConclusionIn establishing the infection control strategies for COVID-19, the variables associated with high infectivity may be considered.