Effect of sibling number in the household and birth order on prevalence of Helicobacter pylori: a cross-sectional study

Accepted 29 August 2007Background Infection with Helicobacter pylori (H. pylori) is acquired mainly in childhood,with studies demonstrating this is related to living conditions. Effects of siblingnumber and birth order on prevalence of infection have not been extensivelystudied.Methods The authors performed a cross-sectional survey of adults, aged between 50 and59 years, previously involved in a community-screening programme for H. pyloriin Leeds and Bradford, UK. Prevalence of H. pylori was assessed at baselinewith urea breath test. All individuals who were alive, and could be traced,were contacted by postal questionnaire in 2003 obtaining information onnumber of siblings and birth order. Data concerning childhood socioeconomicconditions were stored on file from the original study.Results 3928 (47%) of 8407 original participants provided data. Prevalence of infectionincreased according to sibling number (20% in those with none vs 63% witheight or more). Controlling for childhood socioeconomic conditions and birthorder using multivariate logistic regression, infection odds were substantiallyincreased 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 toeight or more siblings (OR 5.70; 95% CI 2.92–11.14). Odds of infection alsoincreased substantially with birth order, but the positive gradient disappearedon adjustment for sibling number and childhood socioeconomic conditions.Conclusions: In this cross section of UK adults, aged 50–59 years, sibling number in thehousehold, but not birth order, was independently associated with prevalenceof H. pylori infection.Keywords Birth order, Helicobacter pylori, prevalence, siblings