Infectious Disease Epidemiology Program

Escherichia coli summary

Shiga toxin-producing Escherichia coli and Hemolytic Uremic Syndrome

Escherichia coli are common bacteria that live in the digestive tract of healthy animals. Many E. coli strains do not cause disease, but some types of E. coli, Shiga toxinproducing Escherichia coli (STEC), make a toxin that can cause significant illness in humans when they ingest the bacteria. The most widely recognized STEC is E. coli 0157:H7. Several other E. coli serotypes, classified as non-0157 serogroups, also cause severe disease and constitute a large proportion of STEC.

STEC infections can cause abdominal cramping, bloody diarrhea, and hemorrhagic colitis. A serious but rare complication, hemolytic uremic syndrome (HUS), which can damage red blood cells and the kidneys, is also associated with STEC infections. Transmission of STEC is usually through consumption of food or water contaminated with fecal matter. Commonly implicated food items include undercooked meats, raw vegetables, and unpasteurized products. STEC can also be passed via contaminated hands from person-to-person or through contact with farm animals.

The STEC case rate for the U.S. in 2007 was 1.7 per 100,000 population. Forty-one cases of STEC were reported to Maine CDC in 2007, resulting in a case rate of 3.1 per 100,000 population. Of the 41 cases reported, 34 were culture-confirmed cases and 7 were classified as probable cases. The median age of STEC cases was 37 years with a range of 1-83 years; the most cases occurred in adults aged 40-64. Twenty-one cases (51%) were female. The counties with the highest case rates were Knox, Kennebec, Lincoln, and Oxford. Although cases were reported in each month, the number of cases peaked in August, September, and October. Four (10%) reported travel outside of the United States before symptom onset. Thirteen (32%) of the cases were hospitalized for an average of 4 days (range 2-7 days). One (2%) of the cases developed HUS, the only reported case of HUS in Maine in 2007. No STEC-related fatalities occurred.

STEC specimens were available for serotyping for all 34 confirmed cases. Of these specimens, 15 (44%) were non-O157 serogroups and 14 (41%) were serogroup O157. Serogroup typing could not be performed on the other 5 (15%) specimens. In addition to serotyping, isolates are compared using pulsed-field gel electrophoresis (PFGE) to identify related cases. PFGE analysis identified 4 STEC clusters, none of which developed into outbreaks. One Maine case was associated with a 2007 multi-state outbreak of E. coli O157:H7 that was linked to packaged, frozen ground beef patties.

STEC prevention measures include: hand washing (particularly before and after cooking and after contact with animals), thoroughly cooking meats, avoiding raw dairy products and unpasteurized juices, avoiding consumption of untreated water, washing fresh fruits and vegetables, and avoiding cross-contamination of food items.