Role of infections in the manifestation or reactivation of inflammatory bowel diseases.

The etiology of inflammatory bowel disease (IBD) is unknown. In addition to genetic and environmental factors, microorganisms have been discussed as possibly playing an important role. Recent reports in the literature do not suggest that a specific persistent infection causes IBD, but indicate that enteric pathogens could cause initial onset of IBD and are associated with reactivation of quiescent disease. Despite their self-limited character, these infections initiate a cascade of inflammatory events leading to chronic, relapsing disease in a genetically susceptible host ("hit-and-run" hypothesis). Epidemiological and microbiologic studies suggest that enteropathogenic microorganisms play a substantial role in the clinical initiation and relapses of IBD. However, similar to traveler's diarrhea, the frequency of infections in the first manifestation and in relapses of IBD is probably understated, due to the problems in detecting enteric pathogens. Thus microbiologic screening is helpful in patients with flares of IBD for optimal medical treatment.