In early August 2011, Minnesota Department of Health (MDH) staff investigated an outbreak of E. coli O157:H7 infections. The first two cases attended a bridal shower potluck held at a church in Waconia, Minnesota on July 24.

Thirty-three guests were interviewed. Six met the case definition for an outbreak case. Three of the 6 were laboratory confirmed. One person was hospitalized. No one developed hemolytic uremic syndrome. No one died.

Foods for the bridal shower were prepared and brought by guests and included ham and chicken salad sandwiches, buns, chicken pasta salad, fresh fruit, fresh veggies and dip, pickles and olives, potato chips and dip, and dessert bars. In a univariate analysis, consuming chicken pasta salad (5 of 6 cases vs. 7 of 26 controls; odds ratio [OR], 13.6; 95% confidence interval [CI], 1.3 to 137.5; p = 0.02), carrots (5 of 6 cases vs. 6 of 24 controls; OR, 15.0; 95% CI, 1.4 to 155.3; p = 0.02), “crazy bars” (4 of 6 cases vs. 4 of 24 controls; OR, 10.0; 95% CI, 1.3 to 74.5; p = 0.03), watermelon (6 of 6 cases vs. 10 of 24 controls; OR, undefined; p =0.02), and strawberries (6 of 6 cases vs. 11 of 24 controls; OR, undefined; p = 0.02) were all significantly associated with illness. A composite variable of any fresh fruit consumption was not statistically significant.

The strawberries and watermelon were purchased from a local grocery store and prepared by a shower attendee who lived in a household with family members who attended a picnic on July 17 at a goat farm. Family members did not report illness in the week following the picnic at the goat farm picnic, but a pattern closely related to the shower outbreak strain (MDH pattern designation MN242ECB47) was isolated from a goat and an environmental sample collected at the goat farm.

Investigators concluded the ultimate source of the outbreak that occurred at the bridal shower was likely the goat farm where a closely related strain of E. coli O157:H7 was found and where household members of the fruit-preparer had attended a potluck 8 days prior to the shower. Contamination of the household environment or direct contact from a household member with an unidentified infection were possible mechanisms of contamination of the fruit.