title: Emergence of antibiotic-resistant non-vaccine serotype pneumococci in nasopharyngeal carriage in children after the use of extended-valency pneumococcal conjugate vaccines in Korea.
abstract: This study was performed to assess the serotype distribution and antibiotic nonsusceptibility of pneumococcal carriage isolates from children in Korea following the introduction of extended-valency pneumococcal conjugate vaccines (PCVs).
  
  
  
  From April to June 2014, nasopharyngeal swabs were collected from children who were attending daycare centers in Korea. The collection was conducted in accordance with the World Health Organization Pneumococcal Carriage Working Group standards. Isolates were identified based on colony morphology, the presence of alpha-hemolysis, and inhibition by optochin test. Serotype was determined by Quellung reaction and sequencing analysis (for serogroup 6). The E-test was performed to determine antibiotic susceptibility.
  
  
  
  A total of 267 pneumococcal isolates were collected from 734 children. Non-PCV13 serotypes accounted for 88.3% and 23A (12.6%), 15B (10.4%), and 15C (9.5%) were most common. Younger age was associated with higher carriage (65.6% vs. 31.2%, P<0.001), while completion of PCV vaccination was associated with lower carriage caused by PCV13 serotypes (7.4% vs. 20.8%, P=0.007). Overall, nonsusceptibility rates were 86.0% to penicillin and 90.5% to erythromycin, with a multidrug resistance rate of 81.5%. Among penicillin-nonsusceptible isolates, those caused by PCV13 serotypes were 11% and non-PCV13 serotypes were 89%. Frequent non-PCV13 serotypes (23A, 15B, and 15C) were all nonsusceptible to both penicillin and erythromycin except one.
  
  
  
  High rates of carriage caused by non-PCV13 serotypes such as 23A, 15B, and 15C that show nonsusceptibilities to penicillin and erythromycin were noted following the introduction of extended-valency PCVs in Korea.
authors.affiliation: Seoul National University Hospital, Republic of Korea.
authors.forename: Young June
authors.initials: YJ
authors.lastname: Choe
authors.affiliation: Seoul National University Hospital, Republic of Korea; Seoul National University College of Medicine, Republic of Korea.
authors.forename: Hoan Jong
authors.initials: HJ
authors.lastname: Lee
authors.affiliation: Seoul National University College of Medicine, Republic of Korea; Seoul National University Bundang Hospital, Republic of Korea.
authors.forename: Hyunju
authors.initials: H
authors.lastname: Lee
authors.affiliation: Kosin University Gospel Hospital, Republic of Korea.
authors.forename: Chi Eun
authors.initials: CE
authors.lastname: Oh
authors.affiliation: Chungnam National University Hospital, Republic of Korea.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Cho
authors.affiliation: Jeju National University Hospital, Republic of Korea.
authors.forename: Jae Hong
authors.initials: JH
authors.lastname: Choi
authors.affiliation: Seoul National University Hospital, Republic of Korea; Seoul National University College of Medicine, Republic of Korea.
authors.forename: Hyun Mi
authors.initials: HM
authors.lastname: Kang
authors.affiliation: Gyeongsang National University Changwon Hospital, Republic of Korea.
authors.forename: In Ae
authors.initials: IA
authors.lastname: Yoon
authors.affiliation: Ajou University Hospital, Republic of Korea.
authors.forename: Hyun Joo
authors.initials: HJ
authors.lastname: Jung
authors.affiliation: Seoul National University Hospital, Republic of Korea; Seoul National University College of Medicine, Republic of Korea. Electronic address: eunchoi@snu.ac.kr.
authors.forename: Eun Hwa
authors.initials: EH
authors.lastname: Choi
mesh_terms: D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D002675:Child, Preschool; D024901:Drug Resistance, Multiple, Bacterial; D004917:Erythromycin; D005260:Female; D000069443:Heptavalent Pneumococcal Conjugate Vaccine / Q000627:therapeutic use; D006801:Humans; D007223:Infant; D008297:Male; D008826:Microbial Sensitivity Tests; D009305:Nasopharynx / Q000382:microbiology; D010406:Penicillins; D011008:Pneumococcal Infections / Q000517:prevention & control*; D022242:Pneumococcal Vaccines / Q000627:therapeutic use*; D056910:Republic of Korea / Q000453:epidemiology; D065288:Serogroup; D013296:Streptococcus pneumoniae / Q000187:drug effects
chemical_list: C586648:10-valent pneumococcal conjugate vaccine; C538862:13-valent pneumococcal vaccine; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D010406:Penicillins; D022242:Pneumococcal Vaccines; D004917:Erythromycin
keywords: Antibiotic; Carriage; Resistance; Serotype; Streptococcus pneumoniae; Vaccine