title: Epidemiological evidence for serotype-independent acquired immunity to pneumococcal carriage.
abstract: BACKGROUND
  Asymptomatic nasopharyngeal carriage is the main reservoir for transmission of Streptococcus pneumoniae. The rate of both carriage and pneumococcal disease decreases with age. To what extent these changes are the result of developing natural immunity is currently a subject of debate.
  
  
  OBJECTIVE
  To study the hypothesis that previous carriage induces serotype-independent protective immunity to new colonization.
  
  
  METHODS
  We compared the rates of pneumococcal acquisition for children with different previous carriage histories. We identified 435 episodes of carriage during the first year of life in follow-up data for 99 Bangladeshi children. Cox regression analysis was adjusted for serotype-specific exposure within the family and other confounding factors.
  
  
  RESULTS
  Previous pneumococcal carriage was associated with serotype-independent protection from subsequent acquisition (hazard ratio, 0.60 [95% confidence interval, 0.39-0.90]), whereas recent serotype-specific exposure within the family was associated with an 8-fold increase in the rate of acquisition for that serotype.
  
  
  CONCLUSIONS
  Our findings are consistent with the hypothesis that serotype-independent protective immunity is stimulated in young children by previous pneumococcal carriage and reduces the rate of new colonization. This immunity has the potential to modulate the development of carriage, irrespective of the colonizing serotype, and to do so starting early in infancy.
authors.affiliation: National Public Health Institute, Department of Vaccines, Helsinki, Finland. simo.granat@helsinki.fi
authors.forename: Simo M
authors.initials: SM
authors.lastname: Granat
authors.forename: Jukka
authors.initials: J
authors.lastname: Ollgren
authors.forename: Elja
authors.initials: E
authors.lastname: Herva
authors.forename: Zakaria
authors.initials: Z
authors.lastname: Mia
authors.forename: Kari
authors.initials: K
authors.lastname: Auranen
authors.forename: P Helena
authors.initials: PH
authors.lastname: Mäkelä
mesh_terms: D001459:Bangladesh; D002648:Child; D005190:Family; D006801:Humans; D009305:Nasopharynx / Q000382:microbiology; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000276:immunology* / Q000635:transmission; D016016:Proportional Hazards Models; D012307:Risk Factors; D012424:Rural Population; D013296:Streptococcus pneumoniae / Q000276:immunology*