Escherichia coli O157 Infection and Hemolytic Uremic Syndrome (HUS), 2007

During 2007, 165 culture-confirmed cases of Escherichia coli O157 infection (3.2 per 100,000 population) were reported. The number of reported cases is similar to the median number of cases reported annually from 1997 to 2006 (median, 168 cases; range, 110 to 219) but represents a 12% increase from the 147 cases reported in 2006 and the highest count since 2001. During 2007, 91 (55%) cases occurred in the metropolitan area. One hundred twenty-six (76%) cases occurred during May through October. The median age of case-patients was 20 years (range, 5 months to 85 years). Twenty-five percent of case-patients were 7 years of age or younger. Seventy (42%) case-patients were hospitalized; the median duration of hospitalization was 3 days (range, 1 to 28 days). None died.

In addition to the 165 culture-confirmed E. coli O157 cases, 67 cases of Shiga-toxin producing E. coli (STEC) infection were identified in 2007. Of those, culture-confirmation was not possible in 24, and therefore it is unknown if those were O157 or another serogroup. Serogroups other than O157 accounted for the remaining 43 STEC cases. E. coli O111, O103 and O26 represented 70% of all non-O157 STEC, with 10 case-isolates of each.

Six E. coli O157 outbreaks were identified during 2007. Four of the outbreaks involved foodborne transmission. One outbreak involved contact with animals, and one involved person-to-person transmission.

From March through May, 10 cases with the same pulsed-field gel electrophoresis (PFGE) subtype of E. coli O157:H7 consumed ground beef purchased at grocery stores of the same chain in the Minneapolis/St. Paul metropolitan area. Seven cases were hospitalized, none developed hemolytic uremic syndrome (HUS). The beef trim used to make this ground beef originated from a processing plant in Cottonwood County.

In June and July, an outbreak of E. coli O157:H7 infections occurred at a home daycare in Ramsey County. Eight of the nine children in the daycare ultimately tested positive for E. coli O157. Two case-patients were hospitalized and one had HUS. The source of infection for the index case was not identified, but person-to-person transmission resulted in all of the additional cases. The index case was infectious when he returned to the daycare, and was most likely the source for the additional cases.

Three cases of E. coli O157:H7 infection in two households with illness onsets in July were associated with the consumption of sirloin ball tip steaks purchased from the same retailer. The source of the steaks was one of two beef processing companies in Kansas.

An outbreak of E. coli O157:H7 infections associated with a potluck dinner at a high school in Hennepin County occurred in July. An investigation was initiated when the MDH foodborne illness hotline received a report of illness among a group of people who attended the potluck. Nine laboratory-confirmed cases of E. coli O157:H7 and 17 probable cases were identified. Baked beans and fruit served at the event were significantly associated with illness. There were reports of a lack of serving utensils at the event, and that utensils were used to serve multiple items. A 5-year-old child who had diarrhea prior to and during the potluck dinner and who had self-served fruit and chips was the most likely source of contamination.

Six Minnesota cases and one Wisconsin case with the same or closely-related PFGE subtype of E. coli O157:H7, and an additional Minnesota case of Shiga-toxin producing E. coli that was not culture-confirmed, attended the Minnesota State Fair in August. All but one of the cases showed cattle or visited the cattle barn.

A multi-state outbreak of E. coli O157:H7 infections associated with the consumption of premade, frozen ground beef patties purchased from the same retailer occurred from August to October. Eleven cases were identified in Minnesota, including four cases of HUS. Three of the 11 cases did not have culture confirmation of their infection. There were 36 additional E. coli O157:H7 isolates reported from 14 other states that had PFGE patterns indistinguishable from the outbreak subtype pattern, including two additional HUS cases. Leftover product collected from case households tested positive for the outbreak PFGE subtype. Packaging material obtained from cases revealed that the products were produced on the same day at approximately the same time. The investigation resulted in a recall of approximately 850,000 pounds of ground beef.

In 2007, 18 HUS cases were reported. There were no fatal cases. From 1997 to 2007, the median annual number of reported HUS cases in Minnesota was 17 (range, 9 to 25), and the overall case fatality rate was 6.6%. In 2007, the median age of HUS case-patients was 4.5 years (range, 1 to 66 years); 13 of the 18 cases occurred in children. All 18 case-patients were hospitalized, with a median hospital stay of 19 days (range, 6 to 122 days). All 18 HUS cases reported in 2007 were post-diarrheal. E. coli O157:H7 was cultured from the stool of 10 (55%) case-patients; there were no non-O157 STEC infections identified among the HUS cases in 2007.

• For up to date information see:E. coli O157:H7 and HUS
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2007