Coronavirus Disease Outbreak in Call Center, South Korea.

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.

A Silent Outbreak of Hepatitis E Virus (HEV) Infection or False-Positive Reaction of Anti-HEV IgM after COVID-19 Vaccination? Epidemiological Investigation of an Outbreak in a Korean Factory Complex in 2022.

Background/Aims: To investigate a reported outbreak of presumed hepatitis E virus (HEV) infection in a Korean food manufacturing facility and to explore the association between anti-HEV immunoglobulin M (IgM) positivity and coronavirus disease 2019 (COVID-19) infection or vaccination. Methods: Twenty-four cases of anti-HEV IgM positivity were reported among 646 workers at the facility in 2022. An epidemiological investigation was conducted, comprising HEV-RNA testing of blood and environmental samples, analysis of group meal records, and an association between anti-HEV IgM positivity and confirmed COVID-19 infection or vaccination. Results: All 24 patients were asymptomatic, with cases spread sporadically across the facility. HEV RNA was not detected in the serum or environmental samples. Four out of 340 meals (1.2%) showed a significantly higher proportion of anti-HEV positivity in each meal intake group than in the non-intake group on certain days. Although the cumulative rate of COVID-19 infection showed no difference, the anti-HEV IgM positive group showed significantly higher proportions of >2 doses of COVID-19 vaccination (83.3% vs 48.7%, p=0.021), vaccination within 90 days (45.8% vs 19.7%, p=0.008), and having the Moderna vaccine administered as the last vaccine (75.0% vs 14.5%, p<0.001) than those of the anti-HEV negative group. In four multivariable models, three or more COVID-19 vaccinations and the Moderna vaccine as the last vaccine were consistently associated with anti-HEV IgM positivity, while the specific day group meal intake was also a significant factor. Conclusions: This epidemiological investigation showed that anti-HEV IgM positivity may occur as a false-positive result related to COVID-vaccination over three times and use of the Moderna vaccine, although a portion of true HEV infection may not be excluded.

Hepatitis A Outbreak in a Facility for the Disabled, Gyeonggi Province, Korea: An Epidemiological Investigation.

OBJECTIVES: The number of cases of hepatitis A virus (HAV) infections has sharply increased in Korea, especially among young adults. In this study, an HAV outbreak in a facility for disabled people was investigated, and we found epidemiological differences both between 2 different generations and between generally abled and disabled groups. METHODS: We analyzed the incubation period and attack rate of an HAV outbreak and investigated the prevalence of HAV antibodies among the staff and residents of a facility for the disabled. We performed a retrospective cohort study during the HAV outbreak, which lasted from February 8 to 25, 2019, including examinations of HAV antibody tests and post-exposure HAV vaccination for the staff or residents of the facility. RESULTS: There were 9 confirmed cases in 2 staff members and 7 residents. Among 53 people (30 staff and 23 residents), except for the 9 confirmed cases and 1 staff member with a known history of HAV infection, HAV seroprevalence was seen in 16.7% of the staff under 40 years of age and 95.2% of those over 40 years of age, while the corresponding rates in the residents were 0.0% and 58.8%, respectively. CONCLUSIONS: This result implies that it is necessary to prioritize HAV vaccination for vulnerable groups and workers of residential care facilities.