title: Increase in the prevalence of allergen skin sensitization in successive birth cohorts.
abstract: BACKGROUND
  Little is known about longitudinal trends in the prevalence of allergen skin sensitization in the general population.
  
  
  OBJECTIVE
  We sought to measure the change in prevalence of allergen skin sensitization over a 9-year period in a cohort of adults and hence to determine whether cross-sectional differences in prevalence between age groups are due to an aging or cohort effect.
  
  
  METHODS
  In 1991 and 2000, we measured skin sensitization, defined as a wheal diameter of 3 mm or larger than that elicited by a saline control, to Dermatophagoides pteronyssinus, cat fur, mixed grass, Aspergillus fumigatus, and Cladosporium herbarum in a cohort of 1339 adults from Nottingham aged between 18 and 71 years in 1991. Subjects were divided into six 9-year successive birth cohorts, and the effects of birth cohort and the within-subject change from 1991 to 2000 were analyzed in a generalized estimating equation logit model.
  
  
  RESULTS
  The unadjusted prevalence of sensitization to any allergen was 30.5% in 1991 and 31.8% in 2000. In cross-sectional analyses the prevalence of sensitization decreased with increasing age at both surveys (risk ratio, 2.15; 95% confidence interval [CI], 1.45-3.17 for 18- to 26-year-old patients relative to 63- to 70-year-old patients in the 1991 survey). In longitudinal analysis there was no within-subject change in sensitization from 1991 to 2000 (adjusted odds ratio, 1.07; 95% CI, 0.97-1.19), but there was a significant cohort effect (adjusted odds ratio per successive 9 year cohort, 1.27; 95% CI, 1.18-1.37).
  
  
  CONCLUSIONS
  The cross-sectional decrease in allergen sensitization with age in the general population arises predominantly from a secular increase in sensitization prevalence with successive birth cohorts and not to a loss of sensitization within subjects over time. As a result of this cohort effect, the prevalence of allergic sensitization has increased in this general adult population sample.
authors.affiliation: University of Nottingham, Division of Respiratory Medicine, Clinical Science Building, City Hospital, Nottingham, United Kingdom.
authors.forename: Emma
authors.initials: E
authors.lastname: Broadfield
authors.forename: Tricia M
authors.initials: TM
authors.lastname: McKeever
authors.forename: Sarah
authors.initials: S
authors.lastname: Scrivener
authors.forename: Andrea
authors.initials: A
authors.lastname: Venn
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Lewis
authors.forename: John
authors.initials: J
authors.lastname: Britton
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D039741:Antigens, Dermatophagoides; D001232:Aspergillus fumigatus / Q000276:immunology; D002963:Cladosporium / Q000276:immunology; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D017449:Dermatitis, Allergic Contact / Q000453:epidemiology*; D005260:Female; D006023:Glycoproteins / Q000276:immunology; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012882:Skin Tests; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D039741:Antigens, Dermatophagoides; D006023:Glycoproteins