County Fair, Washington County, New York

The New York State Department of Health investigated what is believed to be the largest outbreak of waterborne E. coli O157:H7 illness in United States history. The outbreak occurred at a fair in Washington County, New York, in August of 1999 (New York State Department of Health, March, 2000).  A total of 781 persons were identified with suspected infections of E. coli O157:H7 and/or Campylobacter jejuni.  Of these cases 127 persons were culture confirmed to be ill with E. coli O157:H7, 71 individuals were hospitalized, 14 persons exhibited hemolytic uremic syndrome (HUS), and 2 people died.  A household telephone survey indicated that the number of people infected by either pathogen after visiting the Washington County Fair might be as high as 2,800. The environmental and site investigation indicated that unchlorinated water from a well serving the southwestern portion of the fairgrounds was contaminated with E. coli O157:H7 (DOH News, 1999).  Samples of manure collected from a barn located 50 feet from the well and samples from the groundwater flow from the manure storage area located 80 feet from the well tested negative for E. coli O157:H7.  However, samples from the septic system tested positive for E. coli O157:H7.

The shape of the epidemic curve suggested a point source outbreak with the peak of symptom onset occurring on September 1. Considering a typical incubation period of 2-4 days, this suggested that most exposures took place towards the end of the fair. This matched information provided by the patients, 88% of whom visited the fair in the final week.  Consumption of only two food or beverage items, soda with ice or ice in any drink, was reported by a majority of the culture-confirmed case patients. MMWR Weekly (1999) reported that the pulsed-field gel electrophoresis testing by the Wadsworth center indicated that the DNA fingerprints of E. coli O157:H7 isolates from the well, the water distribution system, and most confirmed cases were similar.

The epidemiological investigation of this outbreak concluded that a significant relationship was associated with the incidence of the outbreak and the consumption of beverages purchased from vendors supplied with water from the unchlorinated well. MMWR Weekly (1999) reported that letters were sent to nursing homes, hospitals and schools to exclude the symptomatic personnel and also follow careful hygienic practices to prevent secondary transmission.