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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.

Background Despite high coverage (~98%) of universal varicella vaccination (UVV) in the Republic of Korea since 2005, reduction in the incidence rate of varicella is not obvious. The study aimed to evaluate the vaccine effectiveness (VE) of one-dose UVV by timeline and severity of the disease. Methods All children born in Korea in 2011 were included for this retrospective cohort study that analyzed insurance claims data from 2011–2018 and the varicella vaccination records in the immunization registry. Adjusted hazard ratios by Cox proportional hazard models were used to estimate the VE through propensity score matching by the month of birth, sex, healthcare utilization rate, and region. Results Of the total 421,070 newborns in the 2011 birth cohort, 13,360 were matched for age, sex, healthcare utilization rate, and region by the propensity score matching method. A total of 55,940 (13.29%) children were diagnosed with varicella, with the incidence rate 24.2 per 1000 person-year; 13.4% of vaccinated children and 10.4% of unvaccinated children. The VE of one-dose UVV against any varicella was 86.1% (95% confidence interval [CI], 81.4–89.5) during the first year after vaccination and 49.9% (95% CI, 43.3–55.7) during the 6-year follow-up period since vaccination, resulting in a 7.2% annual decrease of VE. The overall VE for severe varicella was 66.3%. The VE of two-dose compared to one-dose was 73.4% (95% CI, 72.2–74.6). Conclusion We found lower long-term VE in one-dose vaccination and waning of effectiveness over time. Longer follow ups of the vaccinated children as well as appropriately designed studies are needed to establish the optimal strategy in preventing varicella in Korea., Graphical Abstract

Purpose: Mumps meningitis is a common complication of mumps infection; however, information on mumps meningitis in the postvaccine era is limited. The purpose of the present study was to determine factors associated with mumps meningitis and to discuss the effect of vaccination on this disease. Methods: We retrospectively reviewed patients younger than 19 years with mumps, diagnosed at a university hospital in Korea between 2003 and 2013. Patients were divided into groups with and without meningitis, and the clinical features of the 2 groups were compared. Results: The study enrolled 119 patients: 19 patients with meningitis and 100 patients without. Univariate analysis showed that older age (median: 15 years vs. 9.5 years, respectively), a longer interval from last vaccination (median: 10.2 years vs. 4.8 years, respectively), and febrile presentation (94.7% vs. 31.0%, respectively) were significantly associated with mumps meningitis. Sex, number of vaccination doses, bilateral parotitis, and the presence of complications other than meningitis did not differ between the 2 groups. In multivariate logistic regression analysis, age (odds ratio, 1.38; 95% confidence interval, 1.01–1.89; P=0.04) and fever (odds ratio, 30.46; 95% confidence interval, 3.27–283.61; P

Background Invasive bacterial infections in apparently immunocompetent children were retrospectively analyzed to figure causative bacterial organisms in Korea. Methods A total of 947 cases from 25 university hospitals were identified from 2006 to 2010 as a continuance of a previous 10-year period study from 1996 to 2005. Results Escherichia coli (41.3%), Streptococcus agalactiae (27.7%), and Staphylococcus aureus (27.1%) were the most common pathogens in infants < 3 months of age. S. agalactiae was the most prevalent cause of meningitis and pneumonia and E. coli was the major cause of bacteremia without localizing signs in this group. In children 3 to 59 months of age, Streptococcus pneumoniae (54.2%), S. aureus (20.5%), and Salmonella spp. (14.4%) were the most common pathogens. S. pneumoniae was the leading cause of pneumonia (86.0%), meningitis (65.0%), and bacteremia without localizing signs (49.0%) in this group. In children ≥ 5 years of age, S. aureus (62.8%) was the predominant pathogen, followed by Salmonella species (12.4%) and S. pneumoniae (11.5%). Salmonella species (43.0%) was the most common cause of bacteremia without localizing signs in this group. The relative proportion of S. aureus increased significantly over the 15-year period (1996–2010) in children ≥ 3 months of age (P < 0.001), while that of Haemophilus influenzae decreased significantly in both < 3 months of age group (P = 0.036) and ≥ 3 months of age groups (P < 0.001). Conclusion S. agalactiae, E. coli, S. pneumoniae, and S. aureus are common etiologic agents of invasive bacterial infections in Korean children., Graphical Abstract

The clinical spectrum of Mycoplasma pneumoniae pneumonia is widely variable. This study evaluated the clinical manifestations of M. pneumoniae pneumonia in children of different age groups and by the presence of co-detected respiratory virus.This study included children hospitalized with M. pneumoniae pneumonia between 2010 and 2015. At the time of pneumonia diagnosis, a nasopharyngeal aspirate was analyzed for respiratory viruses by reverse transcription-polymerase chain reaction (RT-PCR). The clinical manifestations and laboratory findings were reviewed from medical records.Of the 286 children with M. pneumoniae pneumonia, 84 (29.4%) had a co-detected respiratory virus, with the highest co-detection rate in young children (51.9% of children2 years; P = 0.002). In children2 years, with and without co-detected virus, wheezing occurred in 35.7% and 15.4%, respectively. Among the 202 children without any virus detected, only 6.4% were2 years. These young children showed fewer median days of fever than the children ≥2 years (8 vs. 11 days; P = 0.022). Children ≥2 years tended to have accompanying skin rashes (21.7% vs.7.7%; P = 0.310) and elevated liver enzymes (21.7% vs. 0%; P = 0.075) more frequently than children2 years. Only 53.8% of the patients2 years were treated with macrolide compared with 94.1% of the patients ≥2 years (P0.001).The clinical manifestations of M. pneumoniae pneumonia in young children are milder than those in older children. A high prevalence of co-detected respiratory virus in young children suggests that virus might play a role in making pneumonia clinically apparent in this age group.

Background Infants less than 90 days who present with fever are commonly subject to various invasive procedures due to risk of bacterial infections in this age group. However a great proportion are due to viral infections, including influenza. The aim of this study was to assess the impact of testing influenza in infants < 90 days with fever as well as analyze the subjects’ characteristics to identify which infants should be considered for such testing. Methods Clinical characteristics and trends in influenza virus testing and treatment were analyzed among febrile infants

Background This study investigated the genetic structure of Streptococcus pneumoniae isolates from invasive pneumococcal disease (IPD) in Korean children after national immunization program (NIP) of extended-valency pneumococcal conjugate vaccines (PCVs) in Korea from 2014 to 2017. Methods Invasive isolates were collected from 23 hospitals throughout Korea. IPD cases were identified by isolating pneumococci from normally sterile sites. Each isolate was analyzed using standard microbiological techniques, Quellung reaction, multilocus sequence typing, and antimicrobial susceptibility testing. eBURST v3 software was used to estimate the relationships among the isolates and to assign the strains to a clonal complex (CC). Results Ninety-two pneumococcal isolates were analyzed. The source of isolates were blood (77), cerebrospinal fluid (7), pleural fluid (2), joint fluid (2), deep tissue abscess (2), and peritoneal fluid (2). A total of 38 STs and 17 singletons were assigned. Ten clonal complexes were identified: CC320, CC81, CC166, CC439, CC558, CC880, CC3280, CC9395, CC180, and CC310. New STs were assigned: ST13552, ST13553, ST13554, and ST13602. The serotypes were mostly non-vaccine type (NVTs) (82.6%). The most prevalent STs were ST11189 (17.4%, n = 16, all serotype 10A), ST6945 (10.9%, n = 10, all serotype 12F), ST166 (9.8%, n = 9, serotype 11A [22.2%, n = 2], 13 [22.2%, n = 2], 15B/C [22.2%, n = 2], and 23A [33.3%, n = 3]), and ST320 (6.5%, n = 6, all serotype 19A). Major CCs identified were CC166 (11.9%), CC320 (10.9%), and CC81 (10.9%). Serotypes constituting CC81 and CC166 were all NVTs except 6A (n = 1) and 23F (n = 1) in CC81. CC320 consisted of 19A (n = 9) and 19F (n = 1). The relative proportion of NVTs was 61.3% in major CCs. All major three CCs showed multi-drug resistance. Nonsusceptibility to penicillin (80%) and cefotaxime (100%) was the highest in CC320 (serotype 19A [n = 9, 90.0%] and 19F [n = 1, 10.0%]). Conclusion The introduction of extended-valency PCVs has resulted in the change of genetic structure of isolates from IPD of Korean children. In particular, two common CCs (CC81 and CC166), which previously contained vaccine types, were replaced with the NVTs, while CC320 remains unchanged. Disclosures All authors: No reported disclosures.

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.

Tularemia is a potentially severe zoonotic disease caused by Francisella tularensis. A lack of awareness about tularemia can be embarrassing and could result in delayed treatment because of improper diagnosis. The diagnosis of tularemia is difficult, because the infections are rare and the clinical spectrum is broad. As only 1 adult case has been reported in Korea thus far, pediatricians in Korea may be unfamiliar with tularemia. We report our experience with a 14-year-old male adolescent with tularemia who presented with atypical pneumonia and possible infective endocarditis. Although the infectivity and mortality rates for tularemia are very high if left untreated, we did not suspect tularemia in this case until the incidental isolation of F. tularensis. The present case suggests that clinicians in Korea should be more aware of tularemia. This case also suggests that tularemia should be considered in undetermined cases of atypical pneumonia or acute febrile illness without local signs.