- Post-infectious irritable bowel syndrome (PI-IBS) is a common disorder wherein symptoms of IBS begin after an episode of acute gastroenteritis. The Walkerton Health Study (WHS) was initiated in 2002 to study the long-term outcomes of tragic contamination of its municipal water supply with Escherichia coli and Campylobacter species in 2000. Within a cohort of 2069 adult Walkerton residents with no prior history of chronic gastrointestinal disorders, the incidence of PI-IBS 2 years after the outbreak was 10.1% among subjects with no acute gastroenteritis vs 36.2% among those with clinically suspected gastroenteritis (P<0.001). Long-term follow-up of the WHS cohort has shown PI-IBS to have a favorable prognosis, with spontaneous remission in most patients. A recent meta-analysis of nine cohort studies estimated the pooled odds ratio for developing IBS after enteric infection to be 5.86 (95% CI 3.60-9.54). Risk factors for PI-IBS include female gender, younger age, more severe acute enteric infection, and psychiatric comorbidity. A prevailing hypothesis is that PI-IBS results from a failure to downregulate inflammation after an acute insult from gastroenteritis, a model supported by preliminary studies of intestinal permeability and pro-inflammatory genotypes. Ongoing research is testing the hypothesis that PI-IBS denotes increased susceptibility to more overt inflammatory disorders such as Crohn's disease. Although the Walkerton outbreak of acute gastroenteritis was an awful human tragedy, it is hoped that the WHS will advance our understanding of PI-IBS and improve the outcomes of people who suffer similar tragedies in the future.