title: Clonal replacement among 19A Streptococcus pneumoniae in Massachusetts, prior to 13 valent conjugate vaccination.
abstract: As part of an ongoing study of the response of the Streptococcus pneumoniae population to conjugate vaccination, we applied multi-locus sequence typing (MLST) to 291 isolates sampled from nasopharyngeal carriage in Massachusetts children. We found 94 distinct sequence types (STs), including 19 that had not been previously recorded, and a xpt allele containing a large insertion. Comparison with a similar sample collected in 2007 revealed no significant overall difference in the ST composition (p=0.51) suggesting that the population has reached a new equilibrium following the introduction of 7 valent vaccination in 2000. Within serotypes, a large and statistically significant increase (p=0.014 Fisher's Exact test) was noted in the prevalence of the major multiresistant clone ST 320, which is apparently outcompeting ST 199 among serotype 19A strains. This sample will be used as a baseline to study the future evolution of the pneumococcal population in Massachusetts following introduction of vaccines with higher valency.
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College, London, UK. whanage@hsph.harvard.edu
authors.forename: W P
authors.initials: WP
authors.lastname: Hanage
authors.forename: C J
authors.initials: CJ
authors.lastname: Bishop
authors.forename: G M
authors.initials: GM
authors.lastname: Lee
authors.forename: M
authors.initials: M
authors.lastname: Lipsitch
authors.forename: A
authors.initials: A
authors.lastname: Stevenson
authors.forename: S L
authors.initials: SL
authors.lastname: Rifas-Shiman
authors.forename: S I
authors.initials: SI
authors.lastname: Pelton
authors.forename: S S
authors.initials: SS
authors.lastname: Huang
authors.forename: J A
authors.initials: JA
authors.lastname: Finkelstein
mesh_terms: D015373:Bacterial Typing Techniques; D002353:Carrier State / Q000453:epidemiology / Q000382:microbiology; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D008404:Massachusetts / Q000453:epidemiology; D058885:Multilocus Sequence Typing; D009305:Nasopharynx / Q000382:microbiology; D011008:Pneumococcal Infections / Q000453:epidemiology*; D022242:Pneumococcal Vaccines / Q000008:administration & dosage*; D018571:Sentinel Surveillance; D013296:Streptococcus pneumoniae / Q000145:classification*; D018074:Vaccines, Conjugate / Q000008:administration & dosage
chemical_list: C538862:13-valent pneumococcal vaccine; D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate