In the summer of 2009, the Utah Department of Health investigated an outbreak of E. coli O157:H7. Although 13 out of the 14 cases had eaten ground beef, the ground beef traceback and laboratory testing were all negative. Twelve cases reported attending at least one rodeo within the week prior to illness onset. There were a total of four rodeos named; all had been held in Utah. The rodeos used bulls from the same cattle supplier. A matching strain of STEC O157 was isolated from a dirt sample in one of the rodeo bullpens. Health department officials determined the bulls were the cause of the outbreak and recommended livestock and manure be kept separate from patrons at rodeos to prevent future outbreaks.