title: Early-life exposure to antibacterials and the subsequent development of hayfever in childhood in the UK: case-control studies using the General Practice Research Database and the Doctors' Independent Network.
abstract: BACKGROUND
  Theoretically, antibacterial agents in early life might influence allergic sensitization in two ways: (i) as an indicator of infectious illness, they might be expected to protect against allergy; (ii) alternatively they might increase the risk through effects on the commensal bowel flora. Epidemiological evidence linking the prescription of antibacterial agents in early life to the subsequent development of hayfever is conflicting.
  
  
  OBJECTIVE
  To establish definitively whether an association exists between early-life antibacterial exposure and childhood hayfever diagnosis.
  
  
  METHODS
  Nested case-control studies were based on birth cohorts of children identified within two large UK general practice databases of electronic patient records. One hundred and sixteen thousand and four hundred and ninety-three children from 605 general practices were identified as being continuously registered from birth to at least age 5 years. Seven thousand and ninety-eight cases were diagnosed with hayfever after the age of 2 years. One control per case was matched for practice, birth month, sex and still being registered on case diagnosis date. Odds ratios were derived from conditional logistic regressions within each database followed by pooling using a fixed-effect model.
  
  
  RESULTS
  The pooled odds ratio for hayfever was 1.11, 95% CI (1.03-1.20) if exposed to antibacterials in the first year of life, 1.35 (1.25-1.46) in year 2 and 1.47 (1.37-1.59) in year 3. Adjusting for consultation frequency reduced these odds ratios to 0.92, 1.05 and 1.10, respectively. There was no evidence that broader spectrum antibacterials, exposure in any specific month of year 1 or in the grass pollen season influenced the risk of hayfever.
  
  
  CONCLUSIONS
  These data exclude any important effect of antibacterial exposure in infancy on subsequent hayfever risk. Associations reported in earlier studies have likely been exaggerated through publication bias and by lack of control for the tendency of some families to consult frequently for a range of conditions.
authors: Department of Community Health Sciences, St George's Hospital Medical School, London, UK.
authors: S A
authors: SA
authors: Bremner
authors: I M
authors: IM
authors: Carey
authors: S
authors: S
authors: DeWilde
authors: N
authors: N
authors: Richards
authors: W C
authors: WC
authors: Maier
authors: S R
authors: SR
authors: Hilton
authors: D P
authors: DP
authors: Strachan
authors: D G
authors: DG
authors: Cook
mesh_terms: D000367:Age Factors; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects*; D016022:Case-Control Studies; D002675:Child, Preschool; D016208:Databases, Factual; D011307:Drug Prescriptions / Q000706:statistics & numerical data; D005194:Family Practice; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D016017:Odds Ratio; D010342:Patient Acceptance of Health Care / Q000706:statistics & numerical data; D017594:Publication Bias; D006255:Rhinitis, Allergic, Seasonal / Q000453:epidemiology / Q000209:etiology*; D012307:Risk Factors; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D000900:Anti-Bacterial Agents