Background Coronavirus disease 2019 (COVID-19) has been the most important global issue since December 2019. Although the clinical course of COVID-19 is known to be milder in children than in adults, associated hospitalizations among children have increased since the emergence of contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants and the achievement of a high vaccination rate in adults. Considering these global and domestic situations, we believe that risk stratification in children with COVID-19 is urgently needed for decision making regarding hospitalization priority in children infected with SARS-CoV-2 and vaccination priority against COVID-19. Methods This systematic review and meta-analysis was performed by comprehensively searching the PubMed, EMBASE, Scopus and KoreaMed databases through August 25, 2021. The criteria for enrollment were “severe COVID-19” as poor outcomes (intensive care unit admission, invasive mechanical ventilation, and/or death) and underlying comorbidities before SARS-CoV-2 infection. Results Among 872 screened studies, 17 articles were included in the systematic review, and 10 articles were included in the meta-analysis. Neonate (risk ratio [RR], 2.69; 95% confidence interval [CI], 1.83–3.97), prematurity in young infants (RR, 2.00; 95% CI, 1.63–2.46), obesity (RR, 1.43; 95% CI, 1.24–1.64), diabetes (RR, 2.26; 95% CI, 1.95–2.62), chronic lung disease (RR, 2.62; 95% CI, 1.71–4.00), heart disease (RR, 1.82; 95% CI, 1.58–2.09), neurologic disease (RR, 1.18; 95% CI, 1.05–1.33), and immunocompromised status (RR, 1.44; 95% CI, 1.01–2.04) were significant risk factors for severe COVID-19 in children. In the subgroup analysis, age younger than 3 months (RR, 0.26; 95% CI, 0.11–0.66), asthma (RR, 1.08; 95% CI, 0.98–1.20), and neurodevelopmental disorders (RR, 0.88; 95% CI, 0.75–1.04) were not risk factors for severe COVID-19. Conclusion Children with comorbidities such as obesity, diabetes, heart disease, chronic lung diseases other than asthma, seizure disorders, and an immunocompromised status had a high prevalence of severe COVID-19. Neonate and premature infants had a high risk of severe COVID-19. Defining the high-risk group for severe COVID-19 could help to guide hospital admission and priority for vaccination against SARS-CoV-2.

Mycoplasma pneumoniae is the major pathogen of community-acquired pneumonia in children. The prevalence of macrolide-resistant M. pneumoniae (MRMP) is important owing to the limited alternative therapies for children. We analyzed 111 M. pneumoniae obtained from 107 children admitted for lower respiratory tract infection at Jeju National University Hospital between 2010 and 2015. Macrolide resistance of M. pneumoniae was searched for using polymerase chain reaction (PCR) and sequencing. Of 107 clinical M. pneumoniae, 11 (10.3%) carried macrolide resistance mutations in the 23S rRNA gene. All macrolide resistance mutations were A2063G transitions. We found an acquired A2063G mutation of M. pneumoniae from a patient during macrolide treatment. Patients' characteristics and clinical severity did not differ between those with MRMP and macrolide-sensitive M. pneumoniae, with the exception of frequent pleural effusion in the MRMP group. The prevalence of MRMP (10.3%) in Jeju Island was relatively lower than those of surrounding countries in East Asia. Previous antimicrobial usage and timing of diagnostic test should be considered when determining of macrolide resistance of M. pneumoniae.

Background Parainfluenza virus type 3 (PIV3) and respiratory syncytial virus (RSV) B epidemics occurred in South Korea in late 2021. We investigated epidemiological changes of PIV3 and RSV B infections in Korean children before and during the coronavirus disease 2019 (COVID-19) pandemic. Methods In this multicenter retrospective study, we enrolled patients aged less than 19 years with PIV3 or RSV infection in four university hospitals from January 2018 to January 2022. Demographic and clinical data were extracted from the subject’s medical records and analyzed for each virus. Results A total of 652 children with PIV3 were identified including three epidemics: 216 in 2018, 260 in 2019, and 167 in 2021. Among 627 RSV B cases, 169 were identified in 2017/2018, 274 in 2019/2020, and 115 in 2021/2022. The peak circulation of PIV3 and RSV B epidemics were delayed by 6 and 2 months, respectively, in 2021, compared with those in the pre-COVID-19 period. The median age of PIV3 infections increased in 2021 (21.5 months in 2021 vs. 13.0–14.0 in 2018–2019; P < 0.001), whereas that of RSV B infections remained unchanged (3.6–4.0 months). During the COVID-19 pandemic, less frequent hospitalization rates were observed for both PIV3 and RSV B infections, but more children needed respiratory assistance for RSV B infection in 2021/2022 epidemic (32.5%) than before (14.7–19.4%, P = 0.014). Conclusion We observed changes in the epidemiology and clinical presentation of PIV3 and RSV B infections in Korean children during the COVID-19 pandemic.

Background Data on the clinical characteristics of pediatric patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant infection are limited. We aimed to evaluate the clinical features and outcomes of children with SARS-CoV-2 infection before and after omicron variant dominance in Korea. Methods A multicenter retrospective cohort study was conducted in hospitalized patients aged ≤ 18 years with laboratory-confirmed SARS-CoV-2 infection at five university hospitals in South Korea. The study periods were divided into the delta (from August 23, 2021 to January 2, 2022) and omicron (from January 30 to March 31, 2022). Results In total, 612 hospitalized patients were identified (211, delta; 401, omicron). During the omicron and delta periods, the proportions of individuals with serious illness (moderate, severe, and critical severity) were 21.2% and 11.8%, respectively ( P = 0.034). Compared with the delta period, the proportions of patients with moderate illness increased significantly in the age groups of 0–4 years (14.2% vs. 3.4%) and 5–11 years (18.6% vs. 4.2%) during the omicron period. During the two periods, the proportions of patients with complex chronic diseases (delta, 16.0% vs. 4.3%, P = 0.040; omicron, 27.1% vs. 12.7%; P = 0.002), respiratory diseases except for asthma (delta, 8.0% vs. 0.0%, P = 0.013; omicron, 9.4% vs. 1.6%; P = 0.001), and neurologic diseases (delta, 28.0% vs. 3.2%, P < 0.001; omicron, 40.0% vs. 5.1%, P < 0.001) were significantly higher in patients with serious illness than in those with non-serious illness. During the delta period, the risk for serious illness was higher among patients with obesity (adjusted odds ratio [aOR], 8.18; 95% confidence interval [CI], 2.80–27.36) and neurologic diseases (aOR, 39.43; 95% CI, 6.90–268.3) and aged 12–18 years (aOR, 3.92; 95% CI, 1.46–10.85). However, the presence of neurologic disease (aOR, 9.80; 95% CI, 4.50–22.57) was the only risk factor for serious illness during the omicron period. During the omicron period, the proportions of patients with croup (11.0% vs. 0.5%) and seizures (13.2% vs. 2.8%) increased significantly compared with the delta period. Conclusion Compared with the delta period, the proportions of young children and patients with complex comorbidities were higher during the omicron period in Korea. Patients with complex chronic diseases, especially neurologic diseases, had a high risk of severe coronavirus disease 2019 in the two distinct variant-dominant periods.

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