title: Increased antimicrobial resistance among nonvaccine serotypes of Streptococcus pneumoniae in the pediatric population after the introduction of 7-valent pneumococcal vaccine in the United States.
abstract: BACKGROUND
  The 7-valent pneumococcal conjugate vaccine (PCV7) was introduced in the United States in February 2000. The PROTEKT US study evaluated serotype distribution, PCV7 coverage and antimicrobial susceptibility among Streptococcus pneumoniae isolates collected from children aged 0 to 14 years in 2000 through 2001 (year 1; n = 2033), 2002 through 2003 (year 3; n = 1740) and 2003 through 2004 (year 4; n = 1591).
  
  
  METHODS
  Serotyping was performed by Neufeld Quellung reaction. Antimicrobial susceptibilities were determined centrally according to Clinical Laboratory Standards Institute methodology and interpretive breakpoints.
  
  
  RESULTS
  The proportion of isolates covered by PCV7 (vaccine serotypes) decreased from 65.5% (year 1) to 34.7% (year 3) and to 27.0% (year 4) (P < 0.0001) with similar changes seen at regional and state levels. The most common serotypes in year 4 were nonvaccine serotypes (NVS) 19A (19.0% of all isolates), 6A (7.8%), 3 (7.6%), 15 (6.3%) and 35B (5.8%) and vaccine serotype 19F (12.7%). NVS 19A increased relative to vaccine serotype 19F among isolates expressing the erm(B) + mef(A) macrolide-resistant genotype (P < 0.0001) between year 1 (7.8% [19A] versus 86.7% [19F]) and year 4 (45.5% [19A] versus 51.7% [19F]). Antimicrobial resistance rates (year 1 versus year 4) among NVS from nonblood (respiratory tract) sources increased for penicillin (resistant: 12.7-16.1% [P = 0.0857]; intermediate susceptibility: 20.1-31.5% [P < 0.0001]), erythromycin (21.2-31.6% [P < 0.0001]), amoxicillin-clavulanate (1.4-5.8% [P < 0.0001]) and multidrug resistance (resistance to > or =2 antimicrobial classes) (24.6-31.6% [P = 0.0034]).
  
  
  CONCLUSIONS
  The proportion of S. pneumoniae isolates from U.S. pediatric patients covered by PCV7 decreased substantially in the 4 years after vaccine introduction. However, resistance to commonly used antimicrobials, including beta-lactams and macrolides, as well as multidrug-resistant strains increased significantly among respiratory tract isolates of NVS.
authors.affiliation: G. R. Micro Ltd, London, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Farrell
authors.forename: Keith P
authors.initials: KP
authors.lastname: Klugman
authors.forename: Michael
authors.initials: M
authors.lastname: Pichichero
mesh_terms: D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D022401:Meningococcal Vaccines; D008826:Microbial Sensitivity Tests; D011008:Pneumococcal Infections / Q000382:microbiology* / Q000517:prevention & control; D022242:Pneumococcal Vaccines; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000187:drug effects* / Q000276:immunology / Q000302:isolation & purification; D014481:United States
chemical_list: D000900:Anti-Bacterial Agents; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022401:Meningococcal Vaccines; D022242:Pneumococcal Vaccines