Epidemiology of Respiratory Viruses in Korean Children Before and After the COVID-19 Pandemic: A Prospective Study From National Surveillance System

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic led to a decrease in the seasonal incidence of many respiratory viruses worldwide due to the impact of nonpharmaceutical interventions (NPIs). However, as NPI measures were relaxed, respiratory viral infections re-emerged. We aimed to characterize the epidemiology of respiratory viruses in Korean children during post-COVID-19 pandemic years compared to that before the pandemic.

METHODS

A nationwide prospective ongoing surveillance study has been conducted for detection of respiratory viruses between January 2017 and June 2023. We included data on adenovirus (AdV), human bocavirus (HBoV), human coronavirus (HCoV), human metapneumovirus (HMPV), human rhinovirus (HRV), influenza virus (IFV), parainfluenza virus (PIV), and respiratory syncytial virus (RSV), which were detected in children and adolescents younger than 20 years. We analyzed the weekly detection frequency of individual viruses and the age distribution of the affected children. The study period was divided into prepandemic (2017-2019) and postpandemic (2021-2023) periods.

RESULTS

A total of 19,589 and 14,068 samples were collected in the pre- and postpandemic periods, respectively. The overall detection rate of any virus throughout the study period was 63.1%, with the lowest occurring in the 2nd half of 2020 (50.6%) and the highest occurring in the 2nd half of 2021 (72.3%). Enveloped viruses (HCoV, HMPV, IFV, PIV, and RSV) almost disappeared, but nonenveloped viruses (AdV, HBoV, and HRV) were detected even during the peak of the COVID-19 pandemic. The codetection rate increased from 15.0% prepandemic to 19.1% postpandemic (P < 0.001). During the postpandemic period, a large out-of-season PIV and HMPV epidemic occurred, but the usual seasonality began to be restored in 2023. The mean age of children with each virus detected in 2023 was significantly greater than that in prepandemic years (P = 0.003 and 0.007 for AdV and HCoV, respectively; P < 0.001 for others). The mean age of children with IFV increased in 2022 (11.1 ± 5.2 years) from prepandemic years (7.9 ± 4.6 years) but decreased to 8.7 ± 4.1 years in 2023.

CONCLUSION

With the relaxation of NPI measures, several seasonal respiratory viruses cocirculated with unusual seasonal epidemic patterns and were associated with increasing age of infected children.

Clinical Characteristics and Severity of Respiratory Syncytial Virus Infection in Korean Children during the Post-COVID-19 Pandemic Period

We aimed to evaluate the clinical features of respiratory syncytial virus (RSV) infection and risk factors for severe RSV disease among Korean children in 2022/2023. A total of 235 children were identified, and 84.3% were hospitalized. Patients under 3 months and 2 years of age accounted for 20.9% and 54.5%, respectively. Pneumonia was diagnosed in 40.9% of children and bronchiolitis in 23.8%. Respiratory support and intensive care were required in 43.4% and 7.7% of patients, respectively. Haemophilus influenzae nasopharyngeal colonization and the presence of underlying disease showed a significant correlation with severity indicators. The clinical impact of RSV infection was high on infants and toddlers, even those having no underlying disease or not being indicated for palivizumab.

Community-acquired pneumonia in children: updated perspectives on its etiology, diagnosis, and treatment

Pneumonia is a common pediatric infectious disease that is familiar to pediatricians and a major cause of hospitalization worldwide. Recent well-designed epidemiologic studies in developed countries indicated that respiratory viruses are detected in 30%-70%, atypical bacteria in 7%-17%, and pyogenic bacteria in 2%-8% of children hospitalized with community-acquired pneumonia (CAP). The etiological distribution of CAP varies widely by child age and the epidemiological season of the respiratory pathogen. Moreover, diagnostic tests, particularly for the detection of Streptococcus pneumoniae and Mycoplasma pneumoniae, the 2 major bacterial pathogens involved in pediatric CAP, have several limitations. Therefore, management and empirical antimicrobial therapy for children with CAP should be applied in a stepwise manner based on recent epidemiological, etiological, and microbiological evidence.

First Detection of Enterovirus D68 in Korean Children, September 2022

BACKGROUND

Enterovirus D68 (EV-D68) is a re-emerging pathogen that is particularly common in children and may cause asthma-like respiratory infection and acute flaccid myelitis. However, in Korea, EV-D68 has never been reported thus far. This study aimed to identify EV-D68 from nasopharyngeal aspirates (NPAs) in Korean children with a respiratory tract infection.

MATERIALS AND METHODS

The EV-D68 reference strain was purchased and blindly used to assess the detection ability of three commercial and one in-house mRT-PCR kit in 2018. Then, we selected children whose specimens were positive for human rhinovirus (HRV) and/or enterovirus (EV) by Allplex mRT-PCR (Seegene, Inc., Seoul, Korea) from April to December 2022. Total RNA was extracted from NPAs, and a partial 5'-UTR gene was amplified and sequenced for the identification of HRV/EV species. Additionally, PCR targeting the VP1 gene was performed to assess EV-D68-positive NPAs, followed by sequencing. Phylogenetic analysis and comparison of amino acid sequence alignments were performed using a partial VP1 gene of our and recent international EV-D68 strains.

RESULTS

Among the mRT-PCR kits tested, only the in-house kit was able to detect EV-D68 in 2018. However, we detected three EV-D68 strains among children hospitalized with fever and/or respiratory symptoms in September - December 2022 who tested positive for EV by the Allplex kit. Two of them were healthy toddlers with lower respiratory infections accompanied by new-onset wheezing but no neurologic complications. Among 34 children with lower respiratory infection who tested positive for HRV during the same period, EV-D68 was not detected. Phylogenetic analysis revealed that the first Korean EV-D68 belonged to subclade B3. Amino acid sequence alignment of international subclade B3 EV-D68 strains also showed that our strain is genetically more related to those from Europe than those from Japan.

CONCLUSION

We first detected EV-D68 in three Korean children who had EV detected by the Allplex mRT-PCR kit in 2022. EV-D68 also circulated in Korea in fall 2022, but the prevalence and severity seemed to be lower than those in previous reports from other countries.

Etiology and Clinical Characteristics of Community-Acquired Pneumonia in Korean Children During the Pre-COVID-19 Period, 2015-2020

BACKGROUND

There have been many epidemiologic studies on community-acquired pneumonia (CAP) among children, most of which had substantial limitations. This study investigated the etiologic distribution and clinical characteristics of CAP in Korean children for 5 years before the coronavirus disease 2019 (COVID-19) pandemic.

METHODS

A retrospective analysis of children hospitalized for CAP at 4 referral hospitals during 2015-2020 was performed. Cases in which bronchiolitis was suspected or pulmonary infiltration was not evident on chest radiography (CXR) were excluded. Viruses and atypical bacteria were defined as detected when positive in the polymerase chain reaction test performed for respiratory specimens. Serologic testing result for Mycoplasma pneumoniae was incorporated with strict interpretation. Pyogenic bacteria were included only when cultured in blood, pleural fluid, or bronchoalveolar lavage, but those cultured in endotracheal aspirate or sputum when the case was clinically evident bacterial pneumonia were also included.

RESULTS

A total of 2,864 cases of suspected pneumonia were selected by diagnosis code and CXR findings. Medical chart and CXR review excluded nosocomial pneumonia and cases without evident infiltration, resulting in 517 (18.1%) CAP cases among 489 children. Regarding clinical symptoms, high fever was present in 59.4% and dyspnea in 19.9% of cases. Respiratory support was required for 29.2% of patients, including mechanical ventilation for 3.9%. Pathogens were detected in 49.9% of cases, with viruses in 32.3%, atypical bacteria in 17.8%, and pyogenic bacteria in 2.3% of cases. As single pathogens, M. pneumoniae (16.8%) and respiratory syncytial virus (RSV, 13.7%) were the most common. Parenteral β-lactam and macrolide antibiotics were administered in 81.6% and 50.7% of cases, respectively. A total of 12 (2.3%) cases resulted in poor outcomes, including 3 deaths.

CONCLUSION

M. pneumoniae and RSV were the most commonly detected pathogens of pediatric CAP, which was selected by strict clinical and radiologic criteria. It is necessary to carefully decide whether to use parenteral antibiotics based on the epidemiology and clinical features of CAP in children.

SARS-CoV-2 mRNA Vaccine Elicits Sustained T Cell Responses Against the Omicron Variant in Adolescents

Vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been acknowledged as an effective mean of preventing infection and hospitalization. However, the emergence of highly transmissible SARS-CoV-2 variants of concern (VOCs) has led to substantial increase in infections among children and adolescents. Vaccine-induced immunity and longevity have not been well defined in this population. Therefore, we aimed to analyze humoral and cellular immune responses against ancestral and SARS-CoV-2 variants after two shots of the BNT162b2 vaccine in healthy adolescents. Although vaccination induced a robust increase of spike-specific binding Abs and neutralizing Abs against the ancestral and SARS-CoV-2 variants, the neutralizing activity against the Omicron variant was significantly low. On the contrary, vaccine-induced memory CD4+ T cells exhibited substantial responses against both ancestral and Omicron spike proteins. Notably, CD4+ T cell responses against both ancestral and Omicron strains were preserved at 3 months after two shots of the BNT162b2 vaccine without waning. Polyfunctionality of vaccine-induced memory T cells was also preserved in response to Omicron spike protein. The present findings characterize the protective immunity of vaccination for adolescents in the era of continuous emergence of variants/subvariants.

Two Years of Experience and Methodology of Korean COVID-19 Living Clinical Practice Guideline Development

BACKGROUND

In Korea, during the early phase of the coronavirus disease 2019 (COVID-19) pandemic, we responded to the uncertainty of treatments under various conditions, consistently playing catch up with the speed of evidence updates. Therefore, there was high demand for national-level evidence-based clinical practice guidelines for clinicians in a timely manner. We developed evidence-based and updated living recommendations for clinicians through a transparent development process and multidisciplinary expert collaboration.

METHODS

The National Evidence-based Healthcare Collaborating Agency (NECA) and the Korean Academy of Medical Sciences (KAMS) collaborated to develop trustworthy Korean living guidelines. The NECA-supported methodological sections and 8 professional medical societies of the KAMS worked with clinical experts, and 31 clinicians were involved annually. We developed a total of 35 clinical questions, including medications, respiratory/critical care, pediatric care, emergency care, diagnostic tests, and radiological examinations.

RESULTS

An evidence-based search for treatments began in March 2021 and monthly updates were performed. It was expanded to other areas, and the search interval was organized by a steering committee owing to priority changes. Evidence synthesis and recommendation review was performed by researchers, and living recommendations were updated within 3-4 months.

CONCLUSION

We provided timely recommendations on living schemes and disseminated them to the public, policymakers and various stakeholders using webpages and social media. Although the output was successful, there were some limitations. The rigor of development issues, urgent timelines for public dissemination, education for new developers, and spread of several new COVID-19 variants have worked as barriers. Therefore, we must prepare systematic processes and funding for future pandemics.

Molecular epidemiology of Acinetobacter baumannii complex causing invasive infections in Korean children during 2001-2020

BACKGROUND

Acinetobacter baumannii (AB) has emerged as one of the most problematic pathogens affecting critically ill patients. This study aimed to investigate the longitudinal epidemiology of AB causing invasive diseases in children.

METHODS

Acinetobacter spp. cultured from sterile body fluids and identified as Acinetobacter calcoaceticus-baumannii (ACB) complexes by automated systems from children aged below 19 years old were prospectively collected during 2001-2020. The discriminative partial sequence of rpoB gene was sequenced to identify the species, and sequence types (STs) were determined. Temporal changes in antimicrobial susceptibilities and STs were analyzed.

RESULTS

In total, 108 non-duplicate ACB isolates were obtained from patients with invasive infections. The median age was 1.4 (interquartile range, 0.1-7.9) years, and 60.2% (n = 65) were male. Acinetobacter baumannii comprised 55.6% (n = 60) of the isolates, and the 30-day mortality was higher in patients with isolated AB than in those with non-baumannii Acinetobacter spp. (46.7% vs. 8.3%, P < 0.001). After 2010, complete genotype replacement was observed from non-CC92 genotypes to only CC92 genotypes. Carbapenem resistance rates were highest in AB CC92 (94.2%), followed by AB non-CC92 (12.5%) and non-baumannii Acinetobacter spp. (2.1%). During 2014-2017, which included clustered cases of invasive ST395, colistin resistance increased to 62.5% (n = 10/16), showing a mortality rate of 88% during this period.

CONCLUSION

Complete genotype replacement of non-CC92 with CC92 genotypes was observed. AB CC92 was extensively drug-resistant, and pandrug resistance was observed depending on the ST, warranting careful monitoring.

Non-neuropsychiatric Long COVID Symptoms in Children Visiting a Pediatric Infectious Disease Clinic After an Omicron Surge

Although much interest has emerged regarding post-COVID conditions, data on children and adolescents are limited. The prevalence of long COVID and common symptoms were analyzed in this case-control study of 274 children. Prolonged non-neuropsychiatric symptoms were more frequent in the case group (17.0% and 4.8%, P = 0.004). Abdominal pain (6.6%) was the most common long COVID symptom.

Respiratory syncytial virus infection and the need for immunization in Korea

INTRODUCTION

Respiratory syncytial virus (RSV) infection is one of the most common causes of acute respiratory tract infections in young children and the elderly. Infants and young children aged <2 years and the elderly are at particular risk of severe infections requiring hospitalization.

AREAS COVERED

This narrative review summarizes the epidemiology of RSV infection in Korea, with a particular focus on infants and the elderly, where possible, and highlights the need for effective vaccinations against RSV. Relevant papers were identified from a search of PubMed up to December 2021.

EXPERT OPINION

RSV infection is associated with a significant burden of illness in infants and the elderly worldwide and accounts for a substantial number of hospital admissions due to severe lower respiratory tract infections in both of these age groups in Korea. Vaccination has the potential to reduce the burden of acute RSV-associated disease and long-term consequences such as asthma. Increased understanding of the immune response to RSV, including mucosal immunity, and the innate and adaptive immune responses is needed. Technological advances in vaccine platforms could provide better approaches for achieving a safe and effective vaccine-induced immune response.

Clinical Characteristics and Outcomes of Children With SARS-CoV-2 Infection During the Delta and Omicron Variant-Dominant Periods in Korea

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.

Threshold of Quantitative Cytomegalovirus DNA PCR for Preemptive Treatment in Pediatric Hematopoietic Stem Cell Transplant Recipients

BACKGROUND

Consensus cytomegalovirus (CMV) DNA viral load thresholds for intervention in hematopoietic stem cell transplant (HSCT) recipients have not been established, especially in children. This study aimed at obtaining viral load thresholds of CMV DNA to guide preemptive management in pediatric HSCT recipients.

MATERIALS AND METHODS

A total of 465 blood samples from 177 children who received HSCT between 2015 and 2019 were included in a single center in Korea. The samples were analyzed for CMV infection by both antigenemia assay and quantitative DNA polymerase chain reaction. The 2 assay results were compared for the 233 samples which were collected when antiviral treatment has not been initiated. We determined the viral loads corresponding to the antigenemia of 5 pp65-positive cells/2×10 5 white blood cells (WBCs) as the level for initiating preemptive therapy.

RESULTS

Sixty percent of the samples were collected within 100 days (39.7% in 0 to 50 d, 60.2% in 0 to 100 d) from the graft infusion. The correlation between CMV DNA viral load and CMV antigenemia level increased significantly after 50 days from the graft infusion ( r =0.71 vs. r =0.93, P <0.0001). The correlation was greater in the antiviral treatment-naive group than the treatment group ( r =0.75 vs. r =0.66, P <0.0001). Under receiver operating characteristic curve analysis of the treatment-naive group, the estimated threshold CMV DNA viral loads corresponding to 5 pp65-positive cells/2×10 5 WBCs was 898 IU/mL.

CONCLUSIONS

The CMV DNA levels that corresponded to 5 pp65-positive cells/2×10 5 WBCs was 900 IU/mL in the HSCT group. The proposed viral load thresholds can be used to guide preemptive therapy in pediatric HSCT recipients, especially in the preengraftment period.

Pediatric Deaths Associated With Coronavirus Disease 2019 (COVID-19) in Korea

As of September 3, 2022, 5,388,338 coronavirus disease 2019 (COVID-19) cases and 46 deaths (3 in 2021 and 43 in 2022) were reported in children ≤ 18 years in Korea. Cumulative confirmed cases accounted for 67.3% of the population aged ≤ 18 years and case fatality rate was 0.85/100,000. Among 46 fatal cases, 58.7% were male and median age was 7 years. Underlying diseases were present in 47.8%; neurologic diseases (63.6%) and malignancy (13.6%) most common. Only four had history of COVID-19 immunization. COVID-19 associated deaths occurred at median 2 days from diagnosis (range: -1 to 21). Among COVID-19 deaths, 41.3% occurred before admission; 2 before hospital arrival and 17 in the emergency department. Among children whose cause was documented, myocarditis, respiratory and multiorgan failure were most common. COVID-19 associated death was seen early after diagnosis in children and public health policies to provide access to medical care for children with COVID-19 are essential during the pandemic.

2193. Epidemiology and clinical characteristics of Human adenovirus in Korean children over the past 12 years (2008-2019)

Background

Human adenovirus (HAdV) is a common cause of respiratory tract infection (RTI) and clinical presentation varies by serotype. Serotypes 7 and 55 caused severe pneumonia in children during the early 2000s and in soldiers from 2014 to 2018, respectively, in South Korea. Recent data for the epidemiologic and clinical features of HAdV in Korean children are scarce.

Methods

Nasal aspirates were collected from patients aged 18 years or younger with suspected RTIs at Seoul National University Children's Hospital from 2008 to 2019. HAdV serotype was determined by partial sequencing of hexon gene. The demographics and clinical features were reviewed through medical records.

Results

A total of 186 HAdVs were randomly selected for serotyping among 503 isolates obtained for 12 years. The median age was 2.1 years (range 1 month -17.9 years) with a slight male dominance (60.8%). Ten different serotypes were identified, which included 1-7, 31, 34, 35, and 55. The most predominant serotype was HAdV-3 (n=73, 39.3%) followed by HAdV-2 (n=42, 22.6%). Lower RTI was common in children infected with HAdV-3 (n=40, 54.8%) and HAdV-2 (n=18, 42.9%). HAdV-3 showed an epidemic every three years. HAdV-7 which previously caused severe pneumonia, has not been detected since 2008. HAdV-55 (n=9, 4.9%) was sporadically detected by each one case in 2008, 2009, and 2014, while six cases were detected in 2017-18. Among children with HAdV-55 detected, most (66.7%) had upper RTI as clinical diagnosis and only two (22.2%) had a clinically considerable pneumonia.

Conclusion

Over the past 12 years, HAdV-3 and 2 were prevalent and played an important role in RTIs of Korean children. HAdV-55 infection in children was not clinically significant in comparison to the recent Korean military outbreak cases.

Disclosures

All Authors: No reported disclosures.

SARS-CoV-2 shedding dynamics and transmission in immunosuppressed patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern have been emerging. However, knowledge of temporal and spatial dynamics of SARS-CoV-2 is limited. This study characterized SARS-CoV-2 evolution in immunosuppressed patients with long-term SARS-CoV-2 shedding for 73–250 days, without specific treatment. We conducted whole-genome sequencing of 27 serial samples, including 26 serial samples collected from various anatomic sites of two patients and the first positive sample from patient 2‘s mother. We analysed the intrahost temporal dynamics and genomic diversity of the viral population within different sample types. Intrahost variants emerging during infection showed diversity between individual hosts. Remarkably, N501Y, P681R, and E484K, key substitutions within spike protein, emerged in vivo during infection and became the dominant population. P681R, which had not yet been detected in the publicly available genome in Korea, appeared within patient 1 during infection. Mutually exclusive substitutions at residues R346 (R346S and R346I) and E484 (E484K and E484A) of spike protein and continuous turnover of these substitutions occurred. Unique genetic changes were observed in urine samples. A household transmission from patient 2 to his mother, at least 38 days after the diagnosis, was characterized. Viruses may differently mutate and adjust to the host selective pressure, which could enable the virus to replicate efficiently for fitness in each host. Intrahost variants could be candidate variants likely to spread to the population eventually. Our findings may provide new insights into the dynamics of SARS-CoV-2 in response to interactions between the virus and host.

SARS-CoV-2-Naïve Korean Children and Adolescents Hospitalized With COVID-19 in 2021

BACKGROUND

The risk of severe outcomes with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) delta variant remains low in children and adolescents, but less is known about its effect on the SARS-CoV-2-naïve population. This study evaluated clinical manifestations and risk factors for moderate-to-critical coronavirus disease 2019 (COVID-19) in mostly SARS-CoV-2-naïve children and adolescents in 2021.

METHODS

This multicenter retrospective study included patients aged 0-18 years who were hospitalized with COVID-19 at 8 referring hospitals in South Korea during the predelta-predominant and delta-predominant periods in 2021. Each case was labeled as either hospitalization with medical needs or for isolation. Severity was categorized as mild, moderate, severe, or critical with regard to pneumonia presence and illness severity.

RESULTS

Among 753 cases, most (99.5%) had no prior history of COVID-19 or vaccination against COVID-19. The proportions of hospitalization with medical needs (3.5% vs. 19.7%), moderate illness (0.9% vs. 4.0%), and severe/critical illness (0.8% vs. 5.3%) increased during delta predominance. The risk of moderate-to-critical COVID-19 among hospitalizations with medical needs was higher among patients aged 12-18 years (adjusted odds ratio [aOR], 4.1; 95% confidence interval [CI], 1.5-11.8) and with obesity (aOR, 6.9; 95% CI, 2.4-19.6) but not among patients infected during delta predominance. However, children with obesity experienced more severe COVID-19 during delta predominance (aOR, 6.1; 95% CI, 1.2-29.6).

CONCLUSION

Despite its similar severity among most SARS-CoV-2-naïve children and adolescents, the delta variant may affect COVID-19 severity in those with high-risk underlying medical conditions. Underlying conditions, particularly obesity, may cause severe COVID-19 in children and adolescents, warranting strong consideration for vaccinating high-risk children.

Clinical Characteristics and Prognosis of the Modified Probable Pneumocystis jirovecii Pneumonia in Korean Children, 2001-2021

There are few data about Pneumocystis jirovecii pneumonia (PCP) in children, particularly in developed countries. This study investigated the clinical characteristics and prognosis of the clinical PCP in non-HIV-infected Korean children. Children with positive results for the staining and/or polymerase chain reaction (PCR) for P. jirovecii between 2001 and 2021 were identified. Patients were grouped into clinical PCP, which comprised proven and modified probable cases, and non-PCP groups. Modified probable PCP (mp-PCP) indicate the case which P. jirovecii was detected by conventional PCR rather than real-time PCR test. The differences in demographic and clinical characteristics were analyzed between the groups. A total of 110 pneumonia cases with positive results for P. jirovecii PCR and/or stain were identified from 107 children. Of these, 28.2% were classified as non-PCP, 12.7% of proven PCP, and 59.1% of mp-PCP. Compared with the non-PCP group, the mp-PCP group had a significantly higher rate of solid organ transplantation (3.2% vs. 24.6%), fever (58.1% vs. 76.9%), tachypnea (25.8% vs. 66.2%), dyspnea (48.4% vs. 83.1%), desaturation (48.4% vs. 80.0%), and bilateral ground-glass opacity on chest radiograph (19.4% vs. 73.8%). However, when the mp-PCP group was compared with the proven PCP group, there was no statistically significant difference. For children with clinical PCP, age under 5 years of age (odds ratio [OR] 10.7), hospital-onset (OR 6.9), and desaturation as initial symptom (OR 63.5) were significant risk factors for death in multivariable analysis. Modified probable PCP might reliably reflect true PCP in terms of patient's demographic, clinical features, treatment response, and prognosis. Immunocompromised children with hospital-onset pneumonia who are younger than 5 years of age and have desaturation would be more cautiously and aggressively managed for survival through the screening for P. jirovecii by conventional PCR on appropriate lower respiratory specimens.

Etiology and Epidemiology of Croup before and throughout the COVID-19 Pandemic, 2018-2022, South Korea

Omicron, a recent variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is currently globally dominating. We reviewed the etiology and epidemiology of croup over an approximately 5-year period, with an emphasis on the recent dominance of the Omicron variant. Children less than 5 years of age seen in the emergency department with diagnosis of croup from two large national tertiary hospitals were collected for the period from January 2018 through March 2022. Viral etiologies of the patients were compared with national surveillance data upon circulating respiratory viruses in the community. A total number of 879 croup cases were recognized during the study period. The most common pathogen was SARS-CoV-2 (26.9%), followed by HRV (23.8%), PIV1 (14.6%), PIV3 (13.1%), and CoV NL63 (13.1%), among seventeen respiratory viral pathogens tested by polymerase chain reaction. The viral identification rate was significantly higher in the Omicron period, with most of the pathogens identified as SARS-CoV-2. In the Omicron period, with the exponential increase in the number of COVID-19 cases in the community, croup associated with SARS-CoV-2 significantly increased, with a high detection rate of 97.2% (35 of 36) among croup cases with pathogen identified. The etiologic and epidemiologic data before and throughout the COVID-19 pandemic indicate that the association between croup and infection with the SARS-CoV-2 Omicron variant is highly plausible.

Therapeutics for the treatment of coronavirus disease 2019 in children and adolescents

Coronavirus disease 2019 (COVID-19) is a mild to moderate respiratory illness in most children and adolescents, but a small proportion develop severe or critical illness. Although pediatric clinical trials for the treatment of COVID-19 are sparse, there are some available drugs for children and adolescents with severe COVID-19. This review summarizes clinical data focusing on antiviral agents and immunomodulators for COVID-19 treatment. Additionally, the current recommendations for therapeutics for children and adolescents with COVID-19 are discussed. Remdesivir is suggested for pediatric patients with COVID-19 in the following cases: children and adolescents with severe COVID-19 who need supplemental oxygen without mechanical ventilation; adolescents aged ≥12 years and weight of at least 40 kg with COVID-19 who do not require supplemental oxygen and are within 7 days of symptom onset and are at high risk of progression to severe illness. Nirmatrelvir/ritonavir is considered for adolescents aged ≥12 years and weighing at least 40 kg who do not require supplemental oxygen and are within 5 days of symptom onset and are at high risk of progression to severe disease. Corticosteroids are not recommended in children and adolescents with mild to moderate COVID-19. Corticosteroids are recommended in children and adolescents with severe to critical COVID-19.

Distribution of emm genotypes in group A streptococcus isolates of Korean children from 2012 to 2019

OBJECTIVES

Changes in the epidemiology of group A streptococcus (GAS) infection is related to emm genotype. We studied the distribution of emm genotypes and their antibiotic susceptibility among Korean children.

METHODS

Isolates from children with GAS infection between 2012 and 2019 were collected. emm typing and cluster analysis was performed according to the Centers for Disease Control emm cluster classification. Antimicrobial susceptibility was tested using the E-test and resistance genes were analyzed for macrolide resistant phenotypes.

RESULTS

Among 169 GAS isolates, 115 were from children with scarlet fever. Among invasive isolates, emm1 (6/22, 27.3%), emm12 (4/22, 18.2%), and emm4 (4/22, 18.2%) were most common. In scarlet fever, although emm4 (38/115, 33.0%) was the most prevalent throughout the study period, emm4 was replaced by emm3 (28/90, 31.1%) during an outbreak in 2017-2018. Among all isolates, only 2 (1.2%) exhibited erythromycin resistance and harbored both ermA and ermB genes.

CONCLUSIONS

In this analysis of GAS isolated from Korean children, emm1 was the most prevalent in invasive infection. In scarlet fever, emm4 was prevalent throughout the study period, with an increase in emm3 during 2017-2018. GAS isolates during 2012-2019 demonstrated low erythromycin resistance.

Shift in Clinical Epidemiology of Human Parainfluenza Virus Type 3 and Respiratory Syncytial Virus B Infections in Korean Children Before and During the COVID-19 Pandemic: A Multicenter Retrospective Study

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.

Risk Factors for Severe COVID-19 in Children: A Systematic Review and Meta-Analysis

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.

Preliminary Guidelines for the Clinical Evaluation and Management of Long COVID

Long-lasting coronavirus disease 2019 (COVID-19) symptoms beyond 12 weeks, the so-called ‘long COVID’ have been increasingly reported worldwide. Long COVID can be manifested in various forms, and there is an increasing demand for proper assessment and management. However, it is challenging when trying to determine the best-practice standards of care based on the current evidence because there is no internationally agreed clinical definition or clear treatment pathway. Therefore, the present guidelines have been drafted to provide advice on diagnosis and management based on the latest updated available evidence and the consensus of expert opinion. So far, no standard test and drug treatment can be strongly recommended for patients with long COVID because of a lack of evidence. The present guidelines provide advice based on 12 key questions, including appropriate interventions for long COVID that can be used in clinical practice. Continuous careful observation and studies related to long COVID are needed for the long-term impact of COVID-19 and proper management for long COVID to be determined.

999. Nasal Mucosal Cytokines: Potential Biomarkers for Pediatric Pneumonia Severity and Etiology

Background

Community acquired pneumonia (CAP) is a leading cause of mortality in children &lt; 5 years, but our understanding of disease pathogenesis remains limited. The objective of this study was to define the local host immune response in the respiratory tract by measuring nasal mucosal cytokine (NMC) concentrations (conc.). We hypothesized that NMC represent a potential biomarker to help assessing disease severity and pathogen classification.

Methods

We leveraged nasopharyngeal (NP) samples and clinical data from an observational multicenter study [Children’s Hospital’s Initiative for Research in Pneumonia (CHIRP)] conducted between 2015 and 2018. We measured conc. of 92 NMC using the Olink immunoassay. NMC conc. were compared by severity-defined by need for hospitalization, mild (outpatient) and severe (inpatient), and by identified pathogen using Mann-Whitney U test.

Results

This substudy included 182 children with CAP (mild=61; severe=121) and 30 healthy controls (HC). The pathogens identified included: 101 viruses; 32 bacteria (pyogenic=10; atypical=22); 12 with &gt;1 pathogen; and 37 with no pathogen. Children with severe CAP had greater CCL23 and MCP-3 conc. than those with mild disease (p=0.012; p=0.011 respectively). When comparing NMC profiles of children with CAP of viral and bacterial etiology, the viral group had greater conc. of proinflammatory cytokines IL-6 and TNF, (p=0.0002; p=0.0098 respectively). Further subgroup analysis showed that CAP secondary to influenza virus had greater conc. of IL-6, TNF, and antiviral INF-γ and IP-10 compared with CAP caused by pyogenic bacteria. IL-6 and MCP1-4 were significantly increased in the influenza group compared to the atypical bacteria group.

Quantification of NMC in children with CAP based on disease severity

NMC

nasal mucosal cytokine; CAP: community acquired pneumonia; NPX: normalized protein expression, arbitrary unit used in Olink assay that is log 2 scale. Mann-Whitney test was used to determine differences between mild and severe pneumonia

Quantification of NMC in children with CAP based on pathogen classification

Conclusion

Children with severe CAP had higher monocyte chemoattractant NMC conc. than children with mild disease. Children with viral CAP, particularly influenza, had a more robust mucosal response including both proinflammatory and antiviral NMC than children with bacterial CAP. These findings show differences in NMC conc. based on etiology and disease severity. Further studies are needed to determine whether NMC are reliable predictive biomarkers of CAP etiology and severity.

Disclosures

Lilliam Ambroggio, PhD, MPH, Pfizer Inc (Grant/Research Support) Asuncion Mejias, MD, PhD, MsCS, Janssen (Grant/Research Support, Advisor or Review Panel member)Merck (Grant/Research Support, Advisor or Review Panel member)Roche (Advisor or Review Panel member)Sanofi (Advisor or Review Panel member) Octavio Ramilo, MD, Adagio (Consultant)Bill & Melinda Gates Foundation (Grant/Research Support)Janssen (Grant/Research Support)Lilly (Consultant)Merck (Consultant, Grant/Research Support)NIH (Grant/Research Support)Pfizer (Consultant)SANOFI (Board Member)

1186. Increased Respiratory Syncytial Virus (RSV) Viral Replication Leads to Increased Cytokine Production and Polarized Interferon Response in Infant Mucosal Epithelium

Background

RSV is the most frequent etiology of pediatric lower respiratory tract infection. Most children hospitalized for RSV are previously healthy without known risk factors. Children with mild disease managed as outpatients (OP) have higher viral loads than those hospitalized with severe disease. OP children have higher concentrations of the mucosal interferon (IFN), IFNλ2/3, and IP-10, but no differences in IFNλ1. We examined how RSV replication impacts cytokine production kinetics in the nasal mucosa.

Methods

Primary infant human nasal epithelial (iHNE) cells were collected from nasopharyngeal swabs and cultured on an air-liquid interface. Cultures were infected with 0.1 or 0.001 multiplicity of infection (MOI) of RSV-A, or mock infected. Concentrations of IFN-related (IFNα2, β, γ, λ1, λ2/3, and IP-10) and inflammatory (IL-1β, -6, -12, and TNFα) cytokines secreted to the apical and basolateral surfaces were quantified via immunoassay. Kinetics according to viral inocula were compared by ANOVA with Dunn post-hoc testing of the area under the curve (AUC) for each cytokine. Peak concentrations were compared according to MOI and secretion surface by 2-way ANOVA.

Results

AUC of IFNs in both surfaces of RSV infected cells were significantly higher than those of mock infected. The 0.1 MOI RSV inoculum resulted in significantly higher AUCs for all IFN cytokines on both surfaces than the 0.001 MOI. Peak IFNλ1 concentrations were higher on the apical than basolateral side; peak IFNλ2/3 concentrations were higher on the basolateral side than apical. AUCs of inflammatory cytokines in RSV infection were significantly higher on the basolateral, but not apical, surfaces than mock; all basolateral inflammatory cytokines were higher in the 0.1 MOI than the 0.001 MOI.

Conclusion

Higher RSV inoculum induces higher concentrations of IFN-related cytokines on both sides of epithelial cells, and higher concentrations of inflammatory cytokines on the basolateral side. Differential secretion of IFNλ1 and IFNλ2/3 to the apical and basolateral surfaces suggests they may play different roles in immune response during RSV infection. These data support viral replication as an important factor influencing RSV pathogenesis and severity through cytokine production.

Disclosures

Asuncion Mejias, MD, PhD, MsCS, Janssen (Grant/Research Support, Advisor or Review Panel member)Merck (Grant/Research Support, Advisor or Review Panel member)Roche (Advisor or Review Panel member)Sanofi (Advisor or Review Panel member) Octavio Ramilo, MD, Adagio (Consultant)Bill & Melinda Gates Foundation (Grant/Research Support)Janssen (Grant/Research Support)Lilly (Consultant)Merck (Consultant, Grant/Research Support)NIH (Grant/Research Support)Pfizer (Consultant)SANOFI (Board Member)

Emergence of serotype 10A-ST11189 among pediatric invasive pneumococcal diseases, South Korea, 2014-2019

Replacement with nonvaccine serotypes (NVTs) among invasive pneumococcal diseases (IPDs) after the introduction of extended-valency pneumococcal conjugate vaccines varies in predominant serotypes across countries. This study analyzed changes in serotype distribution through serotyping, multilocus sequence typing, and antimicrobial susceptibility testing of 168 pediatric IPD isolates obtained from a multihospital-based surveillance system during 2014-2019 in South Korea. Vaccine serotypes (VTs) accounted for 16.1% (19A, 10.1%; 6A, 1.8%; and 19F 1.8%), 82.1% were NVTs (10A, 23.8%; 15A, 8.3%; 12F, 6.5%; 15C, 6.5%; and 15B, 6.0%), and three (1.8%) were nontypeable. Serotype 10A was the most common serotype, with a significant increase from 11.5% in 2014 to 33.3% in 2019 (p < 0.05 for the trend). Other NVTs decreased from 70.4% to 41.7% between 2015 and 2019, most notably in serotype 12F (from 14.8% to 0%). Almost all (95.0%) serotype 10A isolates were ST11189, which were multidrug resistant.

Epidemiology and Clinical Features of Myocarditis/Pericarditis before the Introduction of mRNA COVID-19 Vaccine in Korean Children: a Multicenter Study

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.

Clinical Efficacy of Doxycycline for Treatment of Macrolide-Resistant Mycoplasma pneumoniae Pneumonia in Children

In areas with high prevalence of macrolide-resistant Mycoplasma pneumoniae (MRMP) pneumonia, treatment in children has become challenging. This study aimed to analyze the efficacy of macrolides and doxycycline with regard to the presence of macrolide resistance. We analyzed children with MP pneumonia during the two recent epidemics of 2014–2015 and 2019–2020 from four hospitals in Korea. Nasopharyngeal samples were obtained from children with pneumonia for MP cultures and polymerase chain reaction (PCR). Macrolide resistance was determined by the analysis of 23S rRNA gene transition. Time to defervescence and to chest X-ray improvement were analyzed. Of 145 cases, the median age was 5.0 years and MRMP accounted for 59 (40.7%). Among macrolide-susceptible MP (MSMP), 78 (90.7%) were treated with macrolides and 21 (35.6%) in the MRMP group with doxycycline. In MRMP pneumonia, shorter days to defervescence (2 vs. 5 days, p < 0.001) and to chest X-ray improvement (3 vs. 6 days, p < 0.001) in the doxycycline group than in the macrolide group was observed, whereas no differences were observed among children with MSMP pneumonia. Compared to macrolides, treatment with doxycycline resulted in better outcomes with a shorter time to defervescence and to chest X-ray improvement among children with MRMP pneumonia.

Changes in the Etiology and Clinical Characteristics of Pediatric Infective Endocarditis in South Korea

OBJECTIVE

Changes in the epidemiology, clinical manifestations, and outcomes of infective endocarditis (IE) have been reported in recent years. This study was performed to analyze changing trends in the etiology of IE in children in South Korea.

STUDY DESIGN

A retrospective study of children with IE was conducted from 2 hospitals in Korea from 2004 to 2019. IE was defined according to the Modified Duke criteria. We analyzed the etiology and clinical outcome of 96 cases and compared the etiology with that during 1987-1997, as described in a previous study.

RESULTS

A total of 96 cases in 89 children satisfied the modified Duke criteria. The median age was 9.5 years. Preexisting structural heart diseases were identified in 81 cases (84.4%). Ten of the 15 cases with normal heart anatomy had a history of indwelling central venous catheters and underlying noncardiac conditions. Of the 72 identified organisms, common pathogens included Staphylococcus aureus, 24 (32.9%); viridans streptococci, 22 (30.2%); coagulase-negative staphylococci, 14 (19.2%); and Candida species, 7 (9.6). Sixty-three cases (66.7%) required surgical intervention, and the overall fatality rate was 7.9%. Compared with the period of 1987-1997, an increasing trend in the proportion of staphylococci as the etiology of IE in 2004-2019 was observed (26.7% vs. 51.8%, P = 0.029). In addition, S. aureus was associated with the high rate of developing complications (P < 0.05).

CONCLUSION

In South Korea, Gram-positive cocci represent 85% of all etiologic agents of IE in children with an increasing trend in the proportion of staphylococci.

Limited Benefit of Facility Isolation and the Rationale for Home Care in Children with Mild COVID-19

Considering the mild degree of coronavirus disease 2019 (COVID-19) in children and the enormous stress caused by isolation in unfamiliar places, policies requiring mandatory isolation at medical facilities should be reevaluated especially given the impact of the pandemic on the availability of hospital beds. In this study, we assessed the usefulness of facility isolation and the transmissibility of severe acute respiratory syndrome coronavirus 2 by infected children to uninfected caregivers in isolation units at a hospital and a residential treatment center in Seoul during August-November 2020. Fifty-three children were included and median age was 4 years (range, 0-18). All were mildly ill or asymptomatic and isolated for a median duration of 12 days. Thirty percent stayed home longer than 2 days before entering isolation units from symptom onset. Among 15 uninfected caregivers, none became infected when they used facemasks and practiced hand hygiene. The results suggest children with mild COVID-19 may be cared safely at home by a caregiver in conditions with adherence to the preventive measures of wearing facemasks and practicing hand hygiene.

Molecular epidemiology of respiratory syncytial virus for 28 consecutive seasons (1990-2018) and genetic variability of the duplication region in the G gene of genotypes ON1 and BA in South Korea

We investigated the molecular epidemiology of respiratory syncytial virus (RSV) isolated from children during 28 consecutive seasons (1990-2018) and the genetic variability of the duplication region of RSV genotypes ON1 and BA in South Korea. RSV was identified using culture-based methods in Hep-2 cells and was grouped as RSV-A or RSV-B by an immunofluorescence assay. The second hypervariable region of the G gene was sequenced for genotyping. The nucleotide and deduced amino acid sequences of the duplication region of RSV ON1 and BA were analyzed. A total of 670 RSV-A and 233 RSV-B isolates were obtained. For RSV-A, the NA1 genotype predominated during the 2004/2005-2011/2012 seasons. The ON1 genotype was first detected in 2011 and has since replaced all other genotypes. For RSV-B, the GB3 genotype predominated during the 1999/2000-2005/2006 seasons, but the BA genotype also replaced all other genotypes of RSV-B after the first season in which it was isolated (2005/2006). In ON1 and BA genotype RSV strains, novel sequence types of the duplication region of the G gene were identified in 50-95% and 33-80% of the isolates, respectively, in each season. The ON1 and BA9 genotypes are responsible for the current epidemics of RSV infection in South Korea. The sequences in the duplication region of the G gene have evolved continuously and might be sufficient for the identification of specific strains of the RSV-A ON1 and RSV-B BA genotypes.

Cytomegalovirus disease in a retinoblastoma cohort: The role of preemptive screening

BACKGROUND

Cytomegalovirus (CMV) disease is underrecognized in children with retinoblastoma. This study investigated rates of CMV infection and disease in this specific population receiving chemotherapy.

METHODS

From a cohort of 164 patients with retinoblastoma diagnosed from 2011 to 2018, 107 patients were evaluated for CMV infection determined by antigenemia assay or real-time PCR. Preemptive CMV screening was implemented in 2013. CMV disease was diagnosed by tissue biopsy, culture, or ophthalmic examination.

RESULTS

Thirty-seven and 70 patients before and after the screening strategy, respectively, were included. Before screening, 10/37 (27%) were diagnosed with CMV infection during chemotherapy. Among them, 5 (50%) developed CMV disease (hepatitis, pneumonia, and retinitis) and one patient died of CMV pneumonia. During screening, 18/70 (26%) were documented with 36 episodes of CMV infection and 9 patients received 25 preemptive antiviral therapies. Age at chemotherapy tended to be younger in patients with CMV infection, and fewer were seronegative prior to chemotherapy. Patients who started chemotherapy at <12 months of age received preemptive therapies significantly more often than those started at ≥12 months. Two (11%) out of 18 patients with CMV infection developed CMV retinitis and colitis, and there were no fatal cases. Preemptive therapy along with active CMV screening significantly reduced the risk of developing CMV disease, from 14% to 2.9% (P = 0.047).

CONCLUSIONS

Children with retinoblastoma can experience significant morbidity and even mortality from CMV infection during chemotherapy in Korea. Preemptive screening and appropriate antiviral therapy can reduce the development of CMV disease and subsequent mortality.

Successful control of norovirus outbreak in a pediatric ward with multi-bed rooms

BACKGROUND

Norovirus outbreaks in health care facilities are difficult to prevent and control.

METHODS

We describe a norovirus outbreak that occurred in a single pediatric ward with multi-bed rooms.

RESULTS

The outbreak began with 4 clustered cases with acute diarrhea in a pediatric ward between December 22 and 25, 2017. A total of 10 cases were identified during the outbreak, with a cumulative incidence of 8.77%. The median age of the cases was 10 months. Symptoms lasted for a median of 7.5 days, and norovirus shed in stool for a median of 19.5 days. The first 5 cases consecutively developed diarrhea; 4 of them were in the same room. The sixth case, which was linked with the clustered cases, had stayed in the intensive care unit and infected 3 other patients during the stay. After these 4 cases were transferred back to the ward, an additional patient was infected. Strict infection control measures were implemented, and the outbreak was successfully terminated 24 days after the initial case.

CONCLUSIONS

Controlling norovirus outbreak in a pediatric ward with multi-bed rooms is challenging. Early detection of the outbreak and prompt implementation of strict infection control measures are critical.

Clinical features and outcomes of community-acquired late-onset sepsis: Focusing on group B Streptococcus and Escherichia coli

BACKGROUND

Group B Streptococcus (GBS) and Escherichia coli are leading causes of late-onset sepsis (LOS) and bacterial meningitis in neonates and infants. This study aimed to describe clinical characteristics and outcomes of community-acquired (CA) LOS caused by GBS and E. coli.

METHODS

A retrospective observational study was performed in three university hospitals in Korea. All infants aged <90 days who were diagnosed with GBS or E coli CA-LOS from 2011 to 2017 were enrolled. Data on the clinical characteristics and outcomes of GBS and E. coli CA-LOS were compared.

RESULTS

Forty GBS and 43 E. coli CA-LOS cases were identified, which mostly (82/83) included term or near-term infants. Meningitis was identified in 54.1% of GBS CA-LOS cases and in 30.3% of E. coli CA-LOS cases, and 88.4% of E. coli CA-LOS cases involved urosepsis. Ten percent each of GBS and non-uropathogenic E. coli (non-UPEC) meningitis cases and all uropathogenic E. coli (UPEC) meningitis cases were diagnosed by pleocytosis without bacterial growth in the cerebrospinal fluid (CSF). Patients with non-culture-proven meningitis had lower CSF pleocytosis and protein levels and higher CSF/serum glucose ratios than patients with culture-proven meningitis (P < 0.05 for all). One patient died of CA-LOS, which was accompanied by meningitis with extended-spectrum β-lactamase-producing non-UPEC. Neurological complications developed in 22.5% of GBS CA-LOS cases and in 2.3% of E. coli CA-LOS cases.

CONCLUSIONS

Neurological complications were frequently observed in GBS CA-LOS cases, although no mortality was observed. Escherichia coli CA-LOS generally developed as urosepsis, which caused non-culture-proven meningitis and had a favorable outcome.

2708. Genetic Structure of Streptococcus pneumoniae Isolated from Invasive Disease in Korea, 2014–2016

Background

The extended-valency pneumococcal conjugate vaccines (PCVs) were implemented into Korean national immunization program in 2014. This study investigated the change in genetic structures of Streptococcus pneumoniae causing invasive pneumococcal disease (IPD) in Korean children after 10- and 13-valent conjugate vaccine (PCV10 and PCV13, respectively) use.

Methods

Between January 2014 and December 2016, invasive isolates were collected from 23 hospitals throughout Korea. Cases of IPD were defined by isolating pneumococci from normally sterile sites. Each pneumococcal isolate was identified using standard microbiological techniques and serotyped by Quellung reaction. The multi-locus sequence typing (MLST) was analyzed for randomly selected isolates.

Results

A total of 91 pneumococcal isolates were analyzed. Common serotypes were 10A (18.7%), 12F (11.0%), 15A (9.9%), 19A (9.9%), 15B/C (7.7%), 23A (6.6%), 35B (5.5%), and 23B (4.4%). The isolates belonged to 38 sequence types (STs), including 4 newly discovered STs. Of the 4 clonal complexes (CCs), 3 clonal complexes were antibiotic-resistant international clones. CC166 (11.9%) were associated with non-vaccine serotypes (NVTs; 11A, 15B/C, 23A, and 13). Serotypes of CC320 (10.9%) comprised of serotype 19A and 19F. The main serotypes responsible for CC81 (10.9%) were serogroup 15. New serotype-ST combinations were observed, especially in serotype 13 and serogroup 15. Also, a possibility of capsular switch event was noted between serogroup 6 and serogroup 15A.).

Conclusion

The introduction of extended-valency PCVs has resulted in the change of the genetic structure of pneumococcal isolates in Korean children. This study demonstrates that selective pressure from PCV10/13 caused predominant serotypes to be NVTs and genetic changes such as capsular switch events.

Disclosures

All authors: No reported disclosures.

2210. Nasopharyngeal Detection of Streptococcus pneumoniae and Clinical Disease Severity in Children with Community-Acquired Pneumonia (CAP)

Background

Streptococcus pneumoniae is the most common pyogenic bacteria associated with CAP in children, but the proportion of cases might be underestimated because of the low sensitivity of current standard diagnostic methods. Nasopharyngeal (NP) carriage of pneumococcus commonly precedes the development of pneumococcal pneumonia, and facilitates pneumococcus interactions with other respiratory pathogens and the host immune response. This study investigated the relationship between pneumococcal carriage and the severity of CAP in children.

Methods

We conducted a prospective, multicenter, observational study for CAP among previously healthy children aged 2 months through 18 years in six children’s hospitals in Ohio. Blood, pleural fluid, and NP swabs were collected for pathogen detection by culture and/or polymerase chain reaction (PCR). S. pneumoniae was quantified in NP swabs by real-time PCR. Patient management followed the standard of care in each study site.

Results

Among 441 children with radiologically confirmed CAP, 156 (35.4%) had no bacterial or viral pathogens identified as etiologic agents. NP pneumococcal carriage rate in this group was 34.6%. Children with CAP and pneumococcal carriage (53/156) were younger (5.9 vs. 9.6 years, P < 0.001) than those with no carriage (103/156). Median neutrophil counts and median procalcitonin concentrations were significantly higher in the pneumococcal carriage group (12,030 vs. 8,370 cells/mm³ and 1.0 vs. 0.5 mg/dl, respectively; P < 0.05 for both) than in the non-carriage group. Children with documented pneumococcal carriage received respiratory support more frequently (50.0% vs. 28.2%, p = 0.012) and had a longer duration of hospitalization (3.5 ± 3.8 vs. 2.1 ± 2.0 days, P = 0.026) than those without pneumococcal carriage. Age was not associated with any of the variables used to assess clinical disease severity.

Conclusion

Pneumococcal carriage was associated with higher inflammatory markers and greater clinical disease severity in children with CAP in whom no pathogens were identified by standard diagnostics. This suggests that NP carriage of pneumococcus in children with CAP may modulate the host immune response and possibly influence clinical disease severity.

Disclosures

Octavio Ramilo, MD, Bill & Melinda Gates Foundation: Research Grant; Janssen: Research Grant; Merck: Advisory Board; NIH: Research Grant; Ohio Children’s Hospital Association (OCHA): Research Grant; Pfizer: Advisory Board, Consultant, Lectures; Sanofi/Medimmune: Advisory Board.

2619. Clinical Characteristics and Etiology of Community-Acquired Pneumonia in Children: A Contemporary, Prospective, Multicenter Study in Ohio, 2015–2018

Background

Worldwide, pneumonia is the leading cause of death in children <5 years of age and the second most common reason for hospitalization in children in the United States and Europe. This study was designed to describe the clinical characteristics and etiology of community-acquired pneumonia (CAP) in children.

Methods

We conducted a prospective, multicenter, observational study of CAP among previously healthy children aged 2 months through 18 years in six children’s hospitals in Ohio. Blood, pleural fluid, and nasopharyngeal swabs were collected for pathogen detection by culture and/or molecular diagnostics. Patient clinical management including antibiotic therapy and respiratory support, followed the standard of care at each study site. Follow-up information regarding clinical outcomes was collected via a survey 6–8 weeks after enrollment.

Results

We enrolled 441 children (n = 380, 86% hospitalized) with CAP from 2015 to 2018. Median age was 5 years (IQR: 2.1–8.9y). Intensive care and respiratory support were required for 15% and 49% of children, respectively. Consolidation and pleural effusion were identified in 26% and 21%, respectively. Among hospitalized children, 99% received antibiotics during hospitalization, and 91% continued antibiotic treatment at discharge. There were no children with any kind of sequelae or deaths from CAP, but 4.4% were readmitted within 30 days after discharge. Pathogens were identified in 64% patients; including pyogenic bacteria in 4%, atypical bacteria in 9%, and viruses in 56%. A total of 18 (4%) children had both bacterial (9 pyogenic and 9 mycoplasma) and viral pathogens. Among children with a virus detected (n = 245), 17% had more than one virus. The most commonly detected bacteria were M. pneumoniae (n = 39) and S. pneumoniae (n = 10). Rhinovirus was the most common virus detected (RV; n = 81, 28%), followed by respiratory syncytial virus (RSV; n = 75, 26%).

Conclusion

In this multicenter cohort, the most commonly detected viruses in children with CAP were RV and RSV, and M. pneumoniae and S. pneumoniae among bacteria. Clinical outcomes in children with CAP were overall good, but there was a high burden of hospitalization and antibiotic use.

Disclosures

Octavio Ramilo, MD, Bill & Melinda Gates Foundation: Research Grant; Janssen: Research Grant; Merck: Advisory Board; NIH: Research Grant; Ohio Children’s Hospital Association (OCHA): Research Grant; Pfizer: Advisory Board, Consultant, Lectures; Sanofi/Medimmune: Advisory Board.

Community-Acquired Pneumonia in Children: Myths and Facts

Community-acquired pneumonia (CAP) is the leading cause of death in children < 5 years of age worldwide. It is also one of the most frequent infectious diseases in children, leading to large antibiotic use and hospitalization even in the industrialized countries. However, the optimal management of CAP in children is still not well defined. Currently, respiratory viruses are considered the most frequent etiologic agents, but detection of viruses in the upper respiratory tract does not guarantee causation of pneumonia, nor precludes the presence of a bacterial pathogen. In both the upper and lower respiratory tract, respiratory viruses and pathogenic bacteria interact. Emerging evidence indicates that dual viral-bacterial infections function synergistically in many cases and together likely enhance the severity of CAP. Therefore, new and advanced technologies capable of sensitively and specifically discriminating viral, bacterial, and viral-bacterial coinfections are needed. Instead of focusing on the pathogen, analysis of host immune transcriptome profiles from children with CAP can potentially offer diagnostic signatures, help to assess disease severity, and eventually, prognostic indicators. An optimized management strategy by using molecular pathogen testing and transcriptome profiling will facilitate prompt, more appropriate, and targeted therapies, which in turn will lead to improved clinical outcomes in children with CAP.

Clonal Expansion of Macrolide-Resistant Sequence Type 3 Mycoplasma pneumoniae, South Korea

To investigate the genetic background for the emergence of macrolide resistance, we characterized the genetic features of Mycoplasma pneumoniae using multilocus sequence typing. Of the 146 M. pneumoniae strains collected during the 5 consecutive outbreaks of M. pneumoniae pneumonia during 2000–2016 in South Korea, macrolide resistance increased from 0% in the first outbreak to 84.4% in the fifth. Among the 8 sequence types (STs) identified, ST3 (74.7%) was the most prevalent, followed by ST14 (15.1%). Macrolide-susceptible strains comprised 8 different STs, and all macrolide-resistant strains were ST3 (98.3%) except 1 with ST14. The proportion of macrolide-resistant strains in ST3 remained 2.2% (1/46) until the 2006–2007 outbreak and then markedly increased to 82.6% (19/23) during the 2010–2012 outbreak and 95.0% (38/40) during the 2014–2016 outbreak. The findings demonstrated that clonal expansion of ST3 M. pneumoniae was associated with the increase in macrolide resistance in South Korea.

Mycobacterium bovis Osteitis Following Immunization with Bacille Calmette-Guérin (BCG) in Korea

BACKGROUND

Mycobacterium bovis Bacille Calmette-Guérin (BCG) osteitis, a rare complication of BCG vaccination, has not been well investigated in Korea. This study aimed to evaluate the clinical characteristics of BCG osteitis during the recent 10 years in Korea.

METHODS

Children diagnosed with BCG osteitis at the Seoul National University Children's Hospital from January 2007 to March 2018 were included. M. bovis BCG was confirmed by multiplex polymerase chain reaction (PCR) in the affected bone. BCG immunization status and clinical information were reviewed retrospectively.

RESULTS

Twenty-one patients were diagnosed with BCG osteitis and their median symptom onset from BCG vaccination was 13.8 months (range, 6.0-32.5). Sixteen children (76.2%) received Tokyo-172 vaccine by percutaneous multiple puncture method, while four (19.0%) and one (4.8%) received intradermal Tokyo-172 and Danish strain, respectively. Common presenting symptoms were swelling (76.2%), limited movement of the affected site (63.2%), and pain (61.9%) while fever was only accompanied in 19.0%. Femur (33.3%) and the tarsal bones (23.8%) were the most frequently involved sites; and demarcated osteolytic lesions (63.1%) and cortical breakages (42.1%) were observed on plain radiographs. Surgical drainage was performed in 90.5%, and 33.3% of them required repeated surgical interventions due to persistent symptoms. Antituberculosis medications were administered for a median duration of 12 months (range, 12-31). Most patients recovered without evident sequelae.

CONCLUSION

Highly suspecting BCG osteitis based on clinical manifestations is important for prompt management. A comprehensive national surveillance system is needed to understand the exact incidence of serious adverse reactions following BCG vaccination and establish safe vaccination policy in Korea.

2319. Molecular Epidemiology of Staphyloccoccus aureus Isolated From Korean Children

Background

Major community acquired-methicillin-resistant Staphylococcus aureus (CA-MRSA) clones have been reported worldwide including ST1 in Asia, Europe, United States, ST8 in Europe and United States and ST30 in Australia, Europe and South America. Panton–Valentine leukocidin (PVL) positive ST30-SCCmec IV has been reported as an important CA-MRSA in Singapore, Japan and Latin America, however reports in Korean children are limited. Therefore we investigated the antimicrobial resistance and molecular characteristics of S. aureus among children in Korea.

Methods

S. aureus previously isolated from children at Seoul National University Bundang Hospital (2010–2016) were analyzed for multilocus sequence type, SCCmec typing, and PCR of PVL, qac A/B, smr and mupA genes. Electronic medical records were reviewed for clinical data and antibiotic susceptibility results.

Results

A total of 79 isolates from skin and soft-tissue infection (SSTI) (N = 41, 51.9%), bone and joint infection (N = 26, 32.9%) and staphylococcal scalded skin syndrome (SSSS) (N = 12, 15.2%) were included. Among these, 32 (40.5%) were MRSA. Among children with underlying diseases (20.3%, 16/79), 56.3% (9/16) were MRSA. After excluding these cases, among children ≤1 month of age, 84.6% (11/13) were MRSA, whereas in children ≥2 months of age, 95.2% (20/21) of SSTI, and 90.0% (18/20) of bone and joint infection were MSSA. All SSSS cases were MRSA. Among MSSA strains, ST30 (N = 28, 59.6%) was the predominant clone and among ST30, 96.6% (28/29) were MSSA. MRSA strains included ST72-SCCmec IV (N = 15, 46.9%), ST89-SCCmec IV (N = 10, 31.3%), ST 5-SCCmec II (N = 3, 9.4%) and ST1-SCCmec IV (N = 3, 9.4%). ST30 was the most common clone in SSTI and bone and joint infection whereas ST89-SCCmec IV was most common in SSSS. PVL was detected in 3 strains (3.8%, ST30-SCCmec IV N = 1, MSSA ST30 N = 2) and qac A/B in 3 strains (MRSA = 3), smr in 3 strains (MSSA = 1, MRSA=2) and mupA in 7 strains (MRSA = 5, MSSA = 2).

Conclusion

The molecular epidemiology of S. aureus in Korean children differed from other countries. Among children with SSTI and bone and joint infection, ST30 was the predominant strain, and the majority was MSSA. Among MRSA isolates, ST72-SCCmec type IV was the most common clone in SSTI and bone and joint infection, and ST89-SCCmec type IV in SSSS.

Disclosures

H. Lee, National Research Foundation of Korea: Grant Investigator, Grant recipient

2351. Epidemiology and Clinical Characteristics of Parainfluenza Virus Type 4 in Korean Children, 2015–2017

Background

Human parainfluenza viruses (HPIVs) are one of common causes of respiratory tract infections in children. Among the four serotypes (HPIVs 1–4), little is known about the epidemiology and clinical characteristics of HPIV-4. The aim of this study was to identify the epidemiology and the characteristics of HPIV-4 compared with HPIVs 1–3 in Korean children.

Methods

We reviewed medical records of children with HPIV who had been admitted at Seoul National University Children’s Hospital during 2015–2017. Detection of respiratory viruses in nasopharyngeal aspirates was performed using multiplex reverse transcription polymerase chain reaction. Patients who had underlying medical conditions such as chronic respiratory disease, immunodeficiency, congenital heart disease, or concurrent viral infections were excluded.

Results

Of 12,539 samples, 586 (8.1%) were positive for HPIV. By the exclusion criteria, 137 (23.4%) were finally included: 46 (33.6%) for HPIV-3, 34 (24.8%) for HPIV-1 and -4 respectively, 23 (16.8%) for HPIV-2. During the study period, two seasonal outbreaks were observed in each serotype. HPIV-1 was prevalent in September 2015 and August 2016, while HPIV-2 in August 2015 and July 2017. The peak of HPIV-3 infection occurred in July 2016 and May 2017. HPIV-4 was mostly infected from August to September in 2015 and in June 2017. Regardless of serotypes, HPIV was predominantly observed in boys and among children less than 5 years of age (70%); the median age in HPIV-4 was 3.1 (0–18) years. The most common clinical presentation was cough in all serotypes (78.7–88.2%). Sore throat was mainly presented in HPIV-4 infected patients compared with other serotypes (11.8%; P = 0.029). HPIV-4 infection was more often diagnosed as bronchiolitis (32.4%) compared with HPIV-1 (8.8%; P = 0.016) and -2 (8.7%; P = 0.037). Croup was most frequently diagnosed in children with HPIV-2 (21.7%), but no patients with HPIV-4 had croup (P = 0.008).

Conclusion

We observed seasonal peak in HPIV-4 from late spring to autumn. Lower respiratory tract infection was main clinical manifestation in HPIV-4 among hospitalized patients and HPIV-4 is a common respiratory pathogen causing significant morbidity in Korean children during 2015–2017.

Disclosures

All authors: No reported disclosures.

2009. Misidentification Rate of Acinetobacter baumannii Isolated From Invasive Infections in Children

Background

Acinetobacter baumannii (AB) invasive infections are known to have a worse clinical outcome than non-baumannii Acinetobacter infections. However, currently, phenotypic identification by semi-automated commercial identification systems struggle to distinguish Acinetobacter subspecies; especially the four closely related subspecies of the Acinetobacter calcoaceticus–Acinetobacter baumannii (ACB) complex. The purpose of this study was to examine the rate of misidentification of AB isolated from invasive infections in children.

Methods

From January 2001 to December 2017, patients 18 years old and below who were treated for invasive AB infections at Seoul National University Hospital and Chungnam National University Hospital were included. Acinetobacter baumannii, identified by commercial identification systems, cultured from sterile body fluids of the study participants were prospectively collected. The DNA from the stored bacteria were isolated, and subspecies identification was carried out by PCR and sequencing of the partial gyrB gene. Clinical data were retrospectively reviewed.

Results

During the 17-year study period, 113 AB isolates were obtained from patients treated for invasive infections. The median age of the patients was 2 (IQR 0–7) years old and 47 (49.5%) were male. Duplicate isolates were eliminated, and a total 95 isolates underwent further investigation. The isolates were retrieved from the blood (n = 82), peritoneal fluid (n = 8), pleural fluid (n = 2), cerebrospinal fluid (n = 2), and bronchoalveolar fluid (n = 1). Of the AB isolates identified by the commercial identification systems, 55 (57.9%) were AB. Of the non-AB isolates identified by partial gyrB sequencing, 22 (23.2%) were identified as A. nosocomialis, 8 (8.4%) as A. pittii, and 1 (1.1%) as A. calcoaceticus. Non-ACB complex subspecies included A. soli (n = 3), A. seifertii (n = 3), A. iwoffii (n = 1), A. bereziniae (n = 1), and A. junnii (n = 1).

Conclusion

There was a high rate of misidentification of the Acinetobacter subspecies causing invasive infections in children. Further studies are needed to analyze the burden that misidentification has on the treatment and outcome of patients with invasive infections.

Disclosures

H. Lee, Korean Society of Pediatric Infectious Diseases: Member, Research grant.

Genetic diversity of pneumococcal surface protein A in invasive pneumococcal isolates from Korean children, 1991-2016

Pneumococcal surface protein A (PspA) is an important virulence factor of pneumococci and has been investigated as a primary component of a capsular serotype-independent pneumococcal vaccine. Thus, we sought to determine the genetic diversity of PspA to explore its potential as a vaccine candidate. Among the 190 invasive pneumococcal isolates collected from Korean children between 1991 and 2016, two (1.1%) isolates were found to have no pspA by multiple polymerase chain reactions. The full length pspA genes from 185 pneumococcal isolates were sequenced. The length of pspA varied, ranging from 1,719 to 2,301 base pairs with 55.7–100% nucleotide identity. Based on the sequences of the clade-defining regions, 68.7% and 49.7% were in PspA family 2 and clade 3/family 2, respectively. PspA clade types were correlated with genotypes using multilocus sequence typing and divided into several subclades based on diversity analysis of the N-terminal α-helical regions, which showed nucleotide sequence identities of 45.7–100% and amino acid sequence identities of 23.1–100%. Putative antigenicity plots were also diverse among individual clades and subclades. The differences in antigenicity patterns were concentrated within the N-terminal 120 amino acids. In conclusion, the N-terminal α-helical domain, which is known to be the major immunogenic portion of PspA, is genetically variable and should be further evaluated for antigenic differences and cross-reactivity between various PspA types from pneumococcal isolates.

Changes in the Serotype Distribution among Antibiotic Resistant Carriage Streptococcus pneumoniae Isolates in Children after the Introduction of the Extended-Valency Pneumococcal Conjugate Vaccine

This study investigated the serotype distribution and antimicrobial resistance of 3,820 nasopharyngeal Streptococcus pneumoniae isolates from infants and children who presented with respiratory symptoms at Seoul National University Children's Hospital from July 2010 to June 2015 after the introduction of the extended-valency pneumococcal conjugate vaccines (PCVs). Serotypes and antimicrobial susceptibility were determined using the Quellung reaction and E-test, respectively. S. pneumoniae was isolated from 397 (10.4%) specimens. The most common serotypes were 19A (14.0%), 23A (12.8%), 15B/C (10.7%), 11A (10.1%), 6C (7.8%), and 6A (6.3%) among the typeable pneumococci (n = 335). The PCV serotype proportions significantly decreased (59.1% in 2010/11 to 17.0% in 2014/15, P < 0.001), whereas the non-PCV serotype proportions significantly increased (40.9% in 2010/11 to 83.0% in 2014/15, P < 0.001). The non-susceptibility rates for penicillin (oral), penicillin (parenteral, non-meningitis), cefotaxime, and erythromycin were 97.8%, 22.8%, 27.7%, and 95.5%, respectively. The proportions of PCV serotypes responsible for non-susceptibility to penicillin (parenteral, non-meningitis) and multidrug resistance significantly decreased (80.8% to 21.1%, P < 0.001 and 64.3% to 12.3%, P < 0.001, respectively), whereas the non-PCV serotype proportions significantly increased (19.2% to 78.9%, P < 0.001 and 35.7% to 87.7%, P < 0.001, respectively). Serotypes 23A and 15B/C demonstrated significant proportional increase among the antibiotics resistant strains. Thus, the PCV serotype proportions decreased and the non-PCV serotype proportions increased among nasopharyngeal carriage pneumococci after the introduction of extended-valency PCVs in Korea. Antimicrobial non-susceptibility rates for penicillin and erythromycin remain high despite the decrease in the proportion of PCV serotypes responsible for antimicrobial resistance over time.