- BACKGROUND: Escherichia coli O157:H7 is a common cause of bacterial gastroenteritis and may increase the risk of hypertension. We studied the risk of hypertension in pregnancy following a large E. coli O157:H7 outbreak that occurred in Walkerton, Canada, in the year 2000. METHODS: We linked data collected from Walkerton residents to provincial healthcare databases. We studied the pregnancies of three groups of women: two groups from Walkerton (those with and without acute gastroenteritis during outbreak) and a third group from neighboring rural communities unaffected by the outbreak. The primary outcome was a composite of gestational hypertension or preeclampsia. Secondary outcomes were gestational hypertension and preeclampsia examined separately. RESULTS: The median time to pregnancy after cohort entry was five years. The composite outcome was not significantly higher among women with gastroenteritis during the outbreak compared with residents of neighboring communities (8 of 117 (6.8%) versus 96 of 2166 (4.4%) pregnancies, respectively; adjusted relative risk 1.5 (95% confidence interval (CI) 0.8 to 3.2)). When examined separately the risk of preeclampsia was significantly higher among women with gastroenteritis (4 of 117 (3.4%) versus 17 of 2166 (0.8%) pregnancies; adjusted relative risk 3.8 (95% CI 1.3 to 11.6)). However, the risk of preeclampsia was lower than expected in the referent group and overall there were a small number of events in all the groups. CONCLUSION: There was no significant association between E. coli O157:H7 gastroenteritis and our primary assessment of hypertension in pregnancy.