Background: Data on severe acute respiratory syndrome coronavirus-2 transmission from a pediatric index patient to others at the school setting are limited. Epidemiological data on pediatric coronavirus disease 2019 (COVID-19) cases after school opening are warranted. Methods: We analyzed data of the pediatric patients with COVID-19 collected from the press release of the Korea Centers for Disease Control and Prevention. Information on the school opening delay and reopening policies were achieved from the press release of the Korean Ministry of Education. Results: The school openings were delayed three times in March 2020. Online classes started from April 9, and off-line (in-person) classes started from May 20 to June 8 at four steps in different grades of students. There was no sudden increase in pediatric cases after the school opening, and the proportion of pediatric cases among total confirmed cases in the nation around 7.0%. As of July 31, 44 children from 38 schools and kindergartens were diagnosed with COVID-19 after off-line classes started. More than 13,000 students and staffs were tested; only one additional student was found to be infected in the same classroom. The proportions of pediatric patients without information on infection sources were higher in older age groups than in younger age groups (17.4% vs. 52.4%, P = 0.014). In the younger age group, 78.3% of children were infected by family members, while only 23.8% of adolescents in the older age group were infected by family members (P < 0.001). Conclusion: Korea had a successful transition from school closure to online and off-line school opening, which did not cause significant school-related outbreak among the pediatric population.

Results of recent studies on gut microbiota have suggested that obesogenic bacteria exacerbate obesity and metabolic dysfunction in the host when fed a high fat diet (HFD). In order to explore obesity-associated bacterial candidates and their response to diet, the composition of faecal bacterial communities was investigated by analyzing 16S rRNA gene sequences in mice. Dietary intervention with probiotics and Garcinia cambogia extract attenuated weight gain and adipocyte size in HFD-fed mice. To identify obesity-causative microbiota, two statistical analyses were performed. Forty-eight bacterial species were found to overlap between the two analyses, indicating the commonly identified species as diet-driven and obesity-associated, which would make them strong candidates for host-microbiome interaction on obesity. Finally, correlation based network analysis between diet, microbe, and host revealed that Clostridium aminophilum, a hyper-ammonia-producing bacterium, was highly correlated with obesity phenotypes and other associated bacteria, and shown to be suppressed by the combination of probiotics and Garcinia cambogia extract. Results of the present study suggest that probiotics and Garcinia cambogia extract alleviate weight gain and adiposity, in part via differentially modulating the composition of gut microbiota in HFD fed mice.

Kawasaki disease (KD) is an acute febrile systemic vasculitis of early childhood with a predilection for the coronary arteries. Since the recent reports from the North America and European countries on Kawasaki-like disease or multisystem inflammatory syndrome in children (MIS-C) possible association with coronavirus disease-19 (COVID-19), 1,2 we explored whether this has been observed in Korean children. The incidence of KD in Korea is estimated to 217.2 per 100,000 children less than 5 years old, 10-30 fold higher than that of KD in North America and Europe. 3 The first patient with COVID-19 in Korea was identified on January 20, 2020, the first pediatric patients was identified on February 19, and the outbreak surge occurred at the end of February. 4 As of May 18, 2020, the number of pediatric cases (≤ 19 years) confirmed with positive severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) polymerase chain reaction (PCR) result was 768 out of 11,065 (6.9%) in the nation and among those, no case of Kawasaki-like clinical manifestations has been documented. 5 In addition, the number of patients with KD among the total new in-patients were searched in two tertiary referral centers in Seoul, Korea during each three months (February to April) from 2015 to 2020 (Fig. 1). A total of 429 children were diagnosed as KD among 14,714 new in-patients during the period. On average, more than 90% of the KD patients were from 0-5 year-age group. For a fair comparison, the proportion of KD patients hospitalized in these two hospitals out of all KD patients in the nation per year was examined. The total numbers of KD patients in the nation per year were retrieved from the Health Insurance Review and Assessment Service website, and proportions were calculated. 6 These proportions were similar with a range of 1.0% to 1.4% during each three months (February to April) from 2015 to 2019. There was no significant increase in KD-related hospitalization. The numbers of children with KD per 100 new in-patients were 3.5 in 2015, 3.2 in 2016, 3.0 in 2017, 2.9 in 2018, and 2.2 in 2019, and 2.6 in 2020. Despite 50 years of search for viral causality, the etiology of KD remains unknown. For example, coronavirus NL63, 229E and even bocavirus have been suggested for the association with KD but failed to clarify the definite association. 7,8 Epidemiologic reports on a sudden rise in MIS-C or Kawasaki-like disease, mainly in older children, are concerning. Direct detection of SARS-CoV-2 from a patient with MIS-C might suggest its contribution to its clinical manifestation. As the COVID-19 pandemic expands over time, however, the presence of the specific SARS-CoV-2 antibody alone may not be sufficient to explain the causal relationship in which

Background Data on SARS-CoV-2 transmission from a pediatric index patient to others at the school setting are limited. Epidemiologic data on pediatric COVID-19 cases after school opening is warranted. Methods We analyzed data of the pediatric patients with COVID-19 collected from the press release of the Korea Centers for Disease Control and Prevention. Information on the school opening delay and re-opening policies were achieved from the press release from Korean Ministry of Education. Findings The school openings were delayed three times in March 2020. Online classes started from April 9, and off-line classes started from May 20 to June 8 at four steps in different grades of students. There was no sudden increase in pediatric cases after the school opening, and the proportion of pediatric cases remained around 7.0% to 7.1%. As of July 11, 45 children from 40 schools and kindergartens were diagnosed with COVID-19 after off-line classes started. More than 11,000 students and staff were tested; only one additional student was found to be infected in the same classroom. Among those 45, 32 (71.1%) patients had available information for the source of infection. Twenty-five (25/45, 55.6%) were infected by the family members. The proportions of pediatric patients without information on infection sources were higher in older age group (middle and high school students) than in younger age group (kindergarten and elementary school students) (47.6% vs 12.5%, p=0.010). In the younger age group, 79.1% of children were infected by family members, while only 28.6% of adolescents in the older age group were infected by family members (p<0.001). Interpretation Korea had a successful transition from school closure to re-opening with online and off-line classes. Although partial, off-line school opening did not cause significant school-related outbreak among pediatric population although young children and adolescents may have different epidemiologic features.

T he exact number of global confirmed cases of coronavirus disease (COVID-19) in children is unknown. Since the first case report in a child, 2.2%-6.7% of reported cases from China, the United States, the European Union, and the United Kingdom have occurred in children (1-3). In South Korea, 14,305 SARS-CoV-2 cases were diagnosed as of July 31, 2020 (4). Of these cases, 1,028 were in children <19 years of age; the proportions of cases for persons <19 years of age was 7.2% and for persons for <9 years of age was 1.7% (4). The proportion of COVID-19 cases in children in South Korea was higher than that for China (2.2%) and the United States (5.1%) (1,2). This proportion was comparable to that for the European Union and the United Kingdom (6.7%) (3).

Background: Chronic urticaria (CU) has an adverse effect on academic achievement and psychosocial development in children.

Background Korean health authority plans to vaccinate adolescents against coronavirus disease 2019 (COVID-19) starting high school seniors during the summer vacation of 2021. However, the myocarditis/pericarditis following COVID-19 vaccine has been reported recently in adolescents and young adults. This study was performed to answer the urgent questions about the basic epidemiology and clinical course of myocarditis/pericarditis in hospitalized patients prior to the introduction of COVID-19 vaccines in pediatric population. Methods A retrospective medical record analysis including frequency, clinical characteristics, etiology and outcome of myocarditis/pericarditis was conducted in 17 years and younger patients who were hospitalized in two referral hospitals in Korea between 2010 and 2019. Results Total 142 patients with myocarditis (n = 119) and/or pericarditis (n = 23) were identified. Median age was 5.4 years (interquartile range, 0.6–12.9 years; range, 11 days–17.8 years), and male was 61%. In adolescents aged 12–17 years, the male to female ratio was 3.2. Myocarditis/pericarditis occurred 0.70 per 1,000 in-patients during the study period: 0.96 (< 1 year), 0.50 (1–5 years), 0.67 (6–11 years) and 1.22 (12–17 years) per 1,000 in-patients, respectively. There was an increasing tendency for the annual frequency from 0.34 in 2010 to 1.25 per 1,000 in-patients in 2019 ( P = 0.021). Among the 56 (40%) proven pathogens at admission, Mycoplasma pneumoniae (n = 11, 8%) and enterovirus (n = 10, 7%) were most common. Of the 142 patients, 99 (70%) required pediatric intensive care unit care and 10 (7%) received heart transplantation. In addition, 61 patients (61/131, 47%) without heart medication at admission needed heart medication when they were discharged. Eleven (7.7%) patients died, of which five patients were previously healthy. The median age of deceased patients was lower than the survival group (0.8 vs. 6.3 years, P = 0.014). Conclusion The frequency of myocarditis/pericarditis was highest among male adolescent in-patients; however, the outcome was favorable in this group without any mortality.

Background Human mesenchymal stem cells (hMSCs) therapy has recently been considered a promising treatment for atopic dermatitis (AD) due to their immunomodulation and tissue regeneration ability. In our previous studies, we demonstrated that hMSCs alleviate allergic inflammation in murine AD model by inhibiting the activation of mast cells and B cells. Also our phase I/IIa clinical trial showed clinical efficacy and safety of hMSCs in moderate-to-severe adult AD patients. However, hMSCs therapy against atopic dermatitis have had poor results in clinical field. Therefore, we investigated the reason behind this result. We hypothesized that drug–cell interaction could interfere with the therapeutic efficacy of stem cells, and investigated whether coadministration with pimecrolimus, one of the topical calcineurin inhibitors, could influence the therapeutic potential of human umbilical cord blood mesenchymal stem cells (hUCB-MSCs) in AD. Methods hUCB-MSCs were subcutaneously injected to AD-induced mice with or without pimecrolimus topical application. To examine whether pimecrolimus influenced the immunomodulatory activity of hUCB-MSCs, hUCB-MSCs were treated with pimecrolimus. Results Pimecrolimus disturbed the therapeutic effect of hUCB-MSCs when they were co-administered in murine AD model. Moreover, the inhibitory functions of hUCB-MSCs against type 2 helper T (Th2) cell differentiation and mast cell activation were also deteriorated by pimecrolimus treatment. Interestingly, we found that pimecrolimus decreased the production of PGE2, one of the most critical immunomodulatory factors in hUCB-MSCs. And we demonstrated that pimecrolimus downregulated COX2-PGE2 axis by inhibiting nuclear translocation of NFAT3. Conclusions Coadministration of pimecrolimus with hMSCs could interfere with the therapeutic efficacy of hMSCs in atopic dermatitis, and this is the first study that figured out the interaction of hMSCs with other drugs in cell therapy of atopic dermatitis. Therefore, this study might give rise to improvement of the clinical application of hMSCs therapy and facilitate the widespread application of hMSCs in clinical field.