title: Pneumococcal sequence type replacement among American Indian children: a comparison of pre- and routine-PCV7 eras.
abstract: BACKGROUND
  Multi-locus sequence typing (MLST) of pneumococcal isolates collected during an efficacy trial of the 7-valent pneumococcal conjugate vaccine (PCV7) among Navajo and White Mountain Apache children from 1998 to 2000 showed a non-differential expansion of pre-existing sequence types (STs) and only one capsule-switching event in the PCV7-randomized communities. PCV7 was introduced as a routine infant vaccine in October 2000. We assessed variability in PCV7 effectiveness and mechanisms of ST replacement after prolonged routine PCV7 use.
  
  
  METHODS
  We applied MLST to 267 non-vaccine type pneumococcal carriage and invasive disease isolates from Navajo and White Mountain Apache children from 2006 to 2008, and compared them to those from 1998 to 2000. Microarray was used to confirm capsule switching events.
  
  
  RESULTS
  The primary mechanism of ST replacement among Navajo and White Mountain Apache children was expansion of existing STs, although introduction of new STs was an important secondary mechanism. ST199, a majority being serotype 19A, was the most common ST in both eras. Only ST193 (serotype 21) was preferentially expanding in the PCV7 era. Three examples of capsule switching were identified. No variability in vaccine effectiveness by ST was observed.
  
  
  CONCLUSIONS
  We did not observe an influence of ST on PCV7 serotype-specific effectiveness, although some STs may be favored in replacement.
authors.affiliation: Center for American Indian Health, Department of International Health, Johns Hopkins Bloomberg School of Public Health, 621N. Washington Street, Baltimore, MD 21205, United States.
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Scott
authors.forename: William P
authors.initials: WP
authors.lastname: Hanage
authors.forename: Marc
authors.initials: M
authors.lastname: Lipsitch
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Millar
authors.forename: Lawrence H
authors.initials: LH
authors.lastname: Moulton
authors.forename: Jason
authors.initials: J
authors.lastname: Hinds
authors.forename: Raymond
authors.initials: R
authors.lastname: Reid
authors.forename: Mathuram
authors.initials: M
authors.lastname: Santosham
authors.forename: Katherine L
authors.initials: KL
authors.lastname: O'Brien
mesh_terms: D001130:Arizona / Q000453:epidemiology / Q000208:ethnology; D002353:Carrier State / Q000453:epidemiology / Q000208:ethnology / Q000382:microbiology*; D002648:Child; D002675:Child, Preschool; D005838:Genotype; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D007198:Indians, North American; D007223:Infant; D058885:Multilocus Sequence Typing / Q000379:methods*; D009516:New Mexico / Q000453:epidemiology / Q000208:ethnology; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000208:ethnology / Q000382:microbiology* / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification
chemical_list: D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022242:Pneumococcal Vaccines