title: Intensity of exposure and severity of whooping cough.
abstract: OBJECTIVE
  To study the association between intensity of exposure and mortality due to pertussis.
  
  
  METHODS
  Overall 3233 historical records from the main fever hospital in Copenhagen were examined. Exposure status of the whooping cough cases was coded as primary, secondary or multiple cases according to information in the hospital records. Primary cases, infected outside the home, were presumably exposed less intensively to the infectious agent compared to secondary cases, who were infected in the family. Multiple cases were from families with several simultaneous cases, but no clear information on transmission between cases.
  
  
  RESULTS
  Case fatality was strongly related to age, being highest among the infants. Other risk factors were sibship size, exposure status and calendar period. In a multivariate analysis, period, age, and exposure status remained significant. Compared to primary cases, secondary cases and multiple cases had a 2.8 [RR = 2.76 (1.37 - 5.56)] and a two-fold [(RR = 1.99 (1.33 - 2.96)] higher risk of dying.
  
  
  CONCLUSIONS
  Intensity of exposure may be a major determinant of the severity of pertussis infection.
authors.affiliation: Department of Epidemiology Research, Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, Denmark. NMN@SSI.dk
authors.forename: N M
authors.initials: NM
authors.lastname: Nielsen
authors.forename: K
authors.initials: K
authors.lastname: Hedegaard
authors.forename: P
authors.initials: P
authors.lastname: Aaby
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D003428:Cross Infection / Q000453:epidemiology / Q000473:pathology; D003718:Denmark / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D015999:Multivariate Analysis; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D014505:Urban Population; D014917:Whooping Cough / Q000453:epidemiology / Q000473:pathology*