title: Effect of sibling number in the household and birth order on prevalence of Helicobacter pylori: a cross-sectional study.
abstract: BACKGROUND
  Infection with Helicobacter pylori (H. pylori) is acquired mainly in childhood, with studies demonstrating this is related to living conditions. Effects of sibling number and birth order on prevalence of infection have not been extensively studied.
  
  
  METHODS
  The authors performed a cross-sectional survey of adults, aged between 50 and 59 years, previously involved in a community-screening programme for H. pylori in Leeds and Bradford, UK. Prevalence of H. pylori was assessed at baseline with urea breath test. All individuals who were alive, and could be traced, were contacted by postal questionnaire in 2003 obtaining information on number of siblings and birth order. Data concerning childhood socioeconomic conditions were stored on file from the original study.
  
  
  RESULTS
  3928 (47%) of 8407 original participants provided data. Prevalence of infection increased according to sibling number (20% in those with none vs 63% with eight or more). Controlling for childhood socioeconomic conditions and birth order using multivariate logistic regression, infection odds were substantially increased with three siblings compared with none [odds ratio (OR) 1.51; 95% confidence interval (CI) 1.06-2.15], and a gradient of effect continued up to eight or more siblings (OR 5.70; 95% CI 2.92-11.14). Odds of infection also increased substantially with birth order, but the positive gradient disappeared on adjustment for sibling number and childhood socioeconomic conditions.
  
  
  CONCLUSIONS
  : In this cross section of UK adults, aged 50-59 years, sibling number in the household, but not birth order, was independently associated with prevalence of H. pylori infection.
authors: Centre for Digestive Diseases, Leeds General Infirmary, Great George Street, Leeds, UK. alexf12399@yahoo.com
authors: Alexander C
authors: AC
authors: Ford
authors: David
authors: D
authors: Forman
authors: Alastair G
authors: AG
authors: Bailey
authors: Karen J
authors: KJ
authors: Goodman
authors: Anthony T R
authors: AT
authors: Axon
authors: Paul
authors: P
authors: Moayyedi
mesh_terms: D001722:Birth Order; D003430:Cross-Sectional Studies; D018562:Disease Transmission, Infectious; D004415:Dyspepsia / Q000453:epidemiology / Q000382:microbiology; D004739:England / Q000453:epidemiology; D005192:Family Health; D005260:Female; D016481:Helicobacter Infections / Q000453:epidemiology* / Q000635:transmission; D016480:Helicobacter pylori; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015995:Prevalence; D012111:Residence Characteristics; D012307:Risk Factors; D035781:Siblings; D012959:Socioeconomic Factors; D014504:Urban Health