Dairy farm, Pennsylvania

Crump et al (2002) discussed an outbreak of E. coli O157:H7 among visitors to a dairy farm in Pennsylvania in September, 2000. A case control study among the visitors was conducted to identify the risk factors of infection, along with a household survey to determine the rates of diarrheal illness. The total number of confirmed or suspected E. coli O157:H7 cases were determined to be fifty-one. The median age among the patients was four. Eight of the cases developed hemolytic uremic syndrome (HUS). The environmental investigation indicated that 28 of 216 cattle (13%) on the farm were carrying E. coli O157:H7 that yielded an identical pattern when analyzed by pulsed field gel electrophoresis to that observed for the isolates of the patients. The organism was also recovered from various surfaces in public access areas of the farm.

MMWR Weekly (April, 2001) reported that a case control study among the farm visitors was conducted jointly by the CDC, Pennsylvania Department of Health, and Montgomery County Health Department to identify the risk factors. A “confirmed case” was defined as diarrhea in a person within 10 days of visiting the farm on or after September 1, with either E. coli O157 isolated from stool or HUS. A “probable case” was defined as diarrhea in a person within 10 days of visiting the farm on or after September 1. A “control” was defined as a person visiting the farm after September 1 who did not develop diarrhea within 10 days of the visit. Fifty one case patients and ninety two controls were interviewed for this case control study.  The research concluded that this large outbreak of E. coli O157:H7 was most likely a result of contamination of both animal hides and the environment. This study also reported that the data showed hand washing as providing protection against transmission of the pathogen.