title: Capsular serotype-specific attack rates and duration of carriage of Streptococcus pneumoniae in a population of children.
abstract: BACKGROUND
  The relative invasiveness rates (attack rates) of Streptococcus pneumoniae of different capsular serotypes in children are not known. Estimates of capsular serotype invasiveness (designated "invasive odds ratios") that are based on cross-sectional prevalence carriage data have been published, but these estimates could be biased by variation in the duration of carriage.
  
  
  METHODS
  The relative attack rates of invasive pneumococci were measured using national UK surveillance data on invasive pneumococcal disease (IPD) incidence and data on incidence of pneumococcal acquisition from longitudinal studies of nasopharyngeal pneumococcal carriage.
  
  
  RESULTS
  We found significant differences in capsular serotype-specific attack rates. For example, capsular serotypes 4, 14, 7F, 9V, and 18C were associated with rates of >20 IPD cases/100,000 acquisitions, whereas capsular serotypes 23F, 6A, 19F, 16F, 6B, and 15B/C were associated with <10 IPD cases/100,000 acquisitions. There was an inverse relationship between duration of carriage and attack rate by capsular serotype (P<.0001). Attack rates were significantly correlated with invasive odds ratios (P<.0001).
  
  
  CONCLUSIONS
  The capsular serotype is a major determinant of both pneumococcal duration of carriage and attack rate. Published invasive odds ratios are a reliable and practical method of determining capsular serotype invasiveness and will be valuable for investigating and characterizing emerging capsular serotypes in the context of conjugate vaccination.
authors.affiliation: University Department of Paediatrics, Oxford Vaccine Group, John Radcliffe Hospital, University of Oxford, Headington, Oxford, OX3 9DU, United Kingdom.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Sleeman
authors.forename: David
authors.initials: D
authors.lastname: Griffiths
authors.forename: Fiona
authors.initials: F
authors.lastname: Shackley
authors.forename: Linda
authors.initials: L
authors.lastname: Diggle
authors.forename: Sunetra
authors.initials: S
authors.lastname: Gupta
authors.forename: Martin C
authors.initials: MC
authors.lastname: Maiden
authors.forename: E Richard
authors.initials: ER
authors.lastname: Moxon
authors.forename: Derrick W
authors.initials: DW
authors.lastname: Crook
authors.forename: Timothy E A
authors.initials: TE
authors.lastname: Peto
mesh_terms: D002648:Child; D006801:Humans; D008137:Longitudinal Studies; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000635:transmission*; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification / Q000472:pathogenicity*; D006113:United Kingdom