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Background@#The largest outbreak of enterohemorrhagic Escherichia coli (EHEC) O157:H7 occurred at a preschool in South Korea from June 12 to 29, 2020. This study aimed to analyze the epidemiological and clinical characteristics of EHEC infection in this outbreak. @*Methods@#Epidemiological investigation was performed on all 184 children and 19 workers at the preschool using a standard questionnaire to assess symptoms, food intake, attendance, and special activity history. Pulsed-field gel electrophoresis analysis of confirmed cases was performed to determine genetic relevance. @*Results@#During this outbreak, 103 children were affected, whereas only one infection was identified in adults. Of the 103 pediatric patients, 85 had symptoms (82.5%), including diarrhea, abdominal pain, bloody stool, fever, and vomiting. Thirty-two patients (31.1%) were hospitalized, 15 (14.6%) were diagnosed with hemolytic uremic syndrome, and 4 (3.9%) received dialysis treatment. Pulsed-field gel electrophoresis analysis identified 4 genotypes with high genetic relevance (92.3%). Epidemiological investigation revealed that this outbreak might have occurred from ingesting foods stored in a refrigerator with a constant temperature above 10°C, which was conducive to bacterial growth. Despite several measures after outbreak recognition, new infections continued to appear. Therefore, the preschool was forced to close on June 19 to prevent further person-to-person transmission. @*Conclusion@#Our findings from the response to the largest outbreak will help prepare countermeasures against future EHEC outbreak.
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Background@#We 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. @*Methods@#A 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. @*Results@#The 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. @*Conclusion@#Immunisation of household members may help to mitigate the current pandemic.
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BackgroundOmicron variant viruses spread rapidly, even in individuals with high vaccination rates. This study aimed to determine the utility of the antibody against the spike protein level as a predictor of the disease course of COVID-19 in vaccinated patients. MethodsBetween 11 December 2021 and 10 February 2022, we performed a prospective observational cohort study in South Korea, which included patients infected with delta -and -omicron variants. Multivariable logistic regression analysis to determine the association between antibody levels and the outcomes was conducted.The relationship between antibody levels and cycle threshold (Ct) values was confirmed using a generalised linear model. ResultsFrom 106 vaccinated patients (39 delta and 67 omicron), the geometric mean titres of antibodies in patients withfever ([≥]37.5 {degrees}C), hypoxia ([≤]94% of SpO2), pneumonia, C-reactive protein (CRP) elevation (>8 mg/L), or lymphopenia (<1,100 cells/L) were 1,201.5 U/mL, 98.8 U/mL, 774.1 U/mL, 1,335.1 U/mL, and 1,032.2 U/mL, respectively. Increased antibody levels were associated with a decrease in the fever occurrence (adjusted odds ratio [aOR], 0.23; 95% confidence interval [CI], 0.12-0.51), hypoxia (aOR, 0.23; 95% CI, 0.08-0.7), CRP elevation (aOR, 0.52; 95% CI, 0.29-0.0.94), and lymphopenia (aOR, 0.57; 95% CI, 0.33-0.98). Ct values showed a positive correlation between antibody levels (P =0.02). ConclusionAntibody levels are predictive of the clinical course of COVID-19 in vaccinated patients with delta and omicron variant infections. Our data highlight the need for concentrated efforts to monitor patients with SARS-CoV-2 infection who are at risk of low antibody levels. SummaryIn this prospective observation cohort study, antibody level predicts clinical course of breakthrough infection of COVID-19. Fever (aOR 0.23[0.12-0.51], hypoxia (aOR 0.23[0.08-0.7]), CRP elevation(aOR 0.52[0.29-0.0.94] and lymphopenia (aOR 0.57[0.33-0.98]) were inversely correlated with antibody levels.
