Environmental influences on the onset and clinical course of Crohn's disease-part 2: infections and medication use.

The pathogenesis of Crohn's disease (CD) involves host, genetic, and environmental factors. These factors result in disturbances in the innate and adaptive immune systems and composition of the intestinal microbiota. Epidemiologic and migration studies support an environmental component in the development of CD. Environmental risk factors include childhood hygiene, air pollution, breastfeeding, smoking, diet, stress, exercise, seasonal variation, appendectomy, medications, and infections. This 2-part series provides an overview of these external contributors to the development or exacerbation of CD. Part 1, which was published in a previous issue, focused on childhood factors, perinatal influences, and lifestyle choices. Part 2, presented here, details the effects of infections, antibiotics, nonsteroidal anti-inflammatory drugs, and oral contraceptives.