Card and colleagues (Gut 2004;53:246–50) reported that the use of antibiotics could increase the risk of Crohn’s disease, particularly those prescribed 2–5 years prior to the diagnosis (odds ratio 1.32 (95% confidence interval 1.05–1.65)). As the use of drugs acting on the central nervous system and of other prescription drugs such as oral contraceptives was also associated with a diagnosis of Crohn’s disease, the authors concluded that this association is non-specific. Nevertheless, some methodological issues could have had an important impact on the results.

One methodological aspect of the study design …