The authors conducted a case-control study among visitors to a farm to identify risk factors for infection. In addition, a household survey was undertaken to determine the rates of diarrheal illness among these visitors.
An extensive environmental study was also performed to identify sources of E. coli O157:H7 on the farm.
A total of 51 patients with confirmed or suspected E. coli O157:H7 infection were enrolled in the case-control study.
The median age of the patients was 4 years, and the hemolytic-uremic syndrome developed in 8.
|13% of cattle colonized with same E. coli isolate as found in patients.
| New England Journal of Medicine |
The researchers found that contact with calves and their environment was associated with an increased risk of infection, whereas hand washing was protective.
The household survey indicated that visitors to the farm during the outbreak had higher than expected rates of diarrhea.
Environmental studies showed that 28 of the 216 cattle on the farm (13%) were colonized with E. coli O157:H7 that had the same distinct pattern on pulsed-field gel electrophoresis that was found in isolates from the patients.
This organism was also recovered from surfaces that were accessible to the public.
Dr John A. Crump, of the National Center for Infectious Diseases, Centers for Disease Control and Prevention, Altanta, Georgia, said on behalf of his group, "We report a large outbreak of E. coli O157:H7 infections among visitors (predominantly children) to a dairy farm."
"In this outbreak, high rates of carriage of E. coli O157:H7 among calves and young cattle most likely resulted in contamination of both the animals' hides and the environment," he concluded.