title: Shifting genetic structure of invasive serotype 19A pneumococci in the United States.
abstract: BACKGROUND
  Following 7-valent conjugate vaccine introduction in the United States in 2000, invasive serotype (sero19A) pneumococcal disease (IPD) emerged rapidly. Sero19A IPD incidence increased slightly during 2005-2008 (from 2.3 cases to 2.5 cases per 100,000 population), whereas sero19A penicillin resistance (defined as a minimum inhibitor concentration [MIC] ≥2 μg/mL) increased significantly (from 28.7% to 43.7%). To better understand changes, we characterized sero19A isolates recovered during 2004-2008.
  
  
  METHODS
  We performed antimicrobial susceptibility testing on all 2767 sero19A IPD isolates identified through the Centers for Disease Control Active Bacterial Core surveillance during 2004-2008. We genotyped 1804 (96.3%) of 1874 sero19A isolates recovered during 2005-2007 and all 148 year 2008 sero19A isolates from children <5 years of age.
  
  
  RESULTS
  Resistant clonal complex (CC) 320/271(19A) increased from 20.9% (115 of 550) to 32.9% (208 of 633; P < .001) of IPD isolates during 2005-2007, which paralleled increased sero19A penicillin resistance (from 28.7% [163 of 567 isolates] to 39.5% [261 of 661 isolates]; P < .001). Total IPD due to 320/271(19A) increased during 2005-2007 and increased from 2.1 to 3.6 cases per 100,000 population during 2005-2008 in children <5 years of age. The penicillin-susceptible/intermediate, putative vaccine-escape CC695(19A) increased from 7.5% (41 of 550) to 13.6% (85 of 633) of sero19A isolates during 2005-2007 (P = .002).
  
  
  CONCLUSIONS
  Sero19A rates may have plateaued; however, clonal shifts are increasing resistance. Increased IPD caused by CC320/271(19A) and CC695(19A) could reflect additional selective advantages in addition to resistance.
authors.affiliation: Respiratory Diseases Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, USA. bbeall@cdc.gov
authors.forename: Bernard W
authors.initials: BW
authors.lastname: Beall
authors.forename: Robert E
authors.initials: RE
authors.lastname: Gertz
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Hulkower
authors.forename: Cynthia G
authors.initials: CG
authors.lastname: Whitney
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Moore
authors.forename: Angela B
authors.initials: AB
authors.lastname: Brueggemann
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D007223:Infant; D008875:Middle Aged; D017720:Molecular Epidemiology; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000382:microbiology* / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000276:immunology; D011159:Population Surveillance; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000187:drug effects / Q000235:genetics*; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D022242:Pneumococcal Vaccines