title: Infections presenting for clinical care in early life and later risk of hay fever in two UK birth cohorts.
abstract: BACKGROUND
  The 'hygiene hypothesis' proposes that infections in infancy protect against hay fever (HF). We investigated infections during infancy in relation to HF, including rarer ones not previously researched in this context, while examining the role of potential confounding variables.
  
  
  METHODS
  From birth cohorts derived within the General Practice Research Database (GPRD) and Doctors Independent Network (DIN) database of computerized patient records from UK general practice, we selected 3549 case-control pairs, matched for practice, age, sex and control follow-up to case diagnosis. Conditional logistic regressions were fitted for each of 30 infections; behavioural problems (BP) acted as a control condition unrelated to HF. Odds ratios (OR), adjusted for consultation frequency were pooled across the databases using fixed effect models. We also adjusted for sibship size in GPRD and a socioeconomic marker in DIN.
  
  
  RESULTS
  Upper respiratory tract infections, diarrhoea and vomiting and acute otitis media in infancy were each related with a moderately increased risk of HF in both databases, as were BP. These associations were lost on adjustment for consultation frequency. Only bronchiolitis was significantly associated with a reduced pooled risk of HF after adjustment for consultations (OR = 0.8). Adjustment for sibship size in GPRD and a socioeconomic marker in DIN had little impact on the OR.
  
  
  CONCLUSIONS
  Of 30 infectious illnesses investigated, none had strong or consistent associations with HF after adjustment for consultation frequency. Except for bronchiolitis, possibly a chance finding, none of the clinically apparent infections considered appear to have an important role in allergy prevention.
authors.affiliation: Division of Community Health Sciences, St George's, University of London, London, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Bremner
authors.forename: I M
authors.initials: IM
authors.lastname: Carey
authors.forename: S
authors.initials: S
authors.lastname: DeWilde
authors.forename: N
authors.initials: N
authors.lastname: Richards
authors.forename: W C
authors.initials: WC
authors.lastname: Maier
authors.forename: S R
authors.initials: SR
authors.lastname: Hilton
authors.forename: D P
authors.initials: DP
authors.lastname: Strachan
authors.forename: D G
authors.initials: DG
authors.lastname: Cook
mesh_terms: D017668:Age of Onset; D000704:Analysis of Variance; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003141:Communicable Diseases / Q000175:diagnosis* / Q000188:drug therapy / Q000453:epidemiology*; D015897:Comorbidity; D003968:Diarrhea, Infantile / Q000175:diagnosis / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D016017:Odds Ratio; D010033:Otitis Media / Q000175:diagnosis / Q000453:epidemiology; D015995:Prevalence; D012016:Reference Values; D012042:Registries; D012141:Respiratory Tract Infections / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology; D006255:Rhinitis, Allergic, Seasonal / Q000175:diagnosis* / Q000453:epidemiology*; D018570:Risk Assessment; D012720:Severity of Illness Index; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D000900:Anti-Bacterial Agents