For this investigation, a confirmed case was defined as laboratory evidence of STEC serotype
O157 with a pulsed-field gel electrophoresis (PFGE) pattern indistinguishable from the other
confirmed cases. A probable case was defined as diarrhea in an individual who was
epidemiologically linked to a person with a confirmed case. A person with a primary case
attended the house party on May 5, 2014; persons with secondary cases became symptomatic
with diarrhea one to ten days after having contact with an ill person.