Parental Family Structure, Helicobacter Pylori, and Gastric Adenocarcinoma

The study of family of origin (parental family), as contrasted to family of procreation, originally received attention from epidemiology in the context of childhood infectious diseases. Two aspects of parental family have been intensely investigated: sibship size and birth order [1,2]. Larger sibship size increases the likelihood of introduction and spread of infectious agents within the family and tends to be inversely associated with children's average age at infection. Birth order, in the absence of vaccination, has a more specific effect on average age at infection, since first-born children are usually infected when first exposed to the child care or school environment, whereas later-born children tend to be infected earlier, even in utero, by their older siblings.