title: Large outbreak of pertussis among young children in Chicago, 1993: investigation of potential contributing factors and estimation of vaccine effectiveness.
abstract: BACKGROUND
  An outbreak of pertussis from July, 1993, to April, 1994, in Chicago was investigated to identify potential contributing factors.
  
  
  METHODS
  Surveillance was enhanced to identify cases. Information from a vaccination coverage survey was used to define a retrospective cohort to estimate vaccine effectiveness of three or more doses of pertussis vaccine.
  
  
  RESULTS
  The median age of 218 reported cases was 8 months, 46% had Hispanic surnames and cases were clustered geographically. Vaccination status was known for 173 of 191 (91%) children younger than 6 years of age. Of these 173, 90 (52%) were younger than 7 months, and 35 (20%) children at least 7 months of age had received fewer than 3 doses of pertussis vaccine. Pertussis vaccine effectiveness was 76% (95% confidence interval, 29 to 92).
  
  
  CONCLUSIONS
  The limited ability of the current pertussis vaccination schedule to protect young infants accounted for 52% of cases, primary vaccine failure accounted for 28% of cases and failure to vaccinate children on time accounted for 20% of cases in young children. Low vaccine effectiveness did not appear to be a contributing factor.
authors.affiliation: Communicable Disease Division, Chicago Department of Health, IL, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Kenyon
authors.forename: H
authors.initials: H
authors.lastname: Izurieta
authors.forename: S T
authors.initials: ST
authors.lastname: Shulman
authors.forename: E
authors.initials: E
authors.lastname: Rosenfeld
authors.forename: M
authors.initials: M
authors.lastname: Miller
authors.forename: R
authors.initials: R
authors.lastname: Daum
authors.forename: P M
authors.initials: PM
authors.lastname: Strebel
mesh_terms: D015984:Causality; D002641:Chicago / Q000453:epidemiology; D002675:Child, Preschool; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000008:administration & dosage* / Q000276:immunology; D004196:Disease Outbreaks; D006801:Humans; D007223:Infant; D010567:Pertussis Vaccine / Q000008:administration & dosage / Q000276:immunology; D014611:Vaccination / Q000706:statistics & numerical data*; D014917:Whooping Cough / Q000453:epidemiology* / Q000517:prevention & control
chemical_list: D015721:Diphtheria-Tetanus-Pertussis Vaccine; D010567:Pertussis Vaccine