A Waterborne Outbreak of Escherichia coli O157:H7 Infections and Hemolytic Uremic Syndrome: Implications for Rural Water Systems

Sonja J. Olsen, Gayle Miller, Thomas Breuer, Malinda Kennedy, Charles Higgins, Jim Walford, Gary McKee, Kim Fox, William Bibb, Paul Mead


Emerging Infectious Diseases. 2002;8(4) 

In This Article

Abstract and Introduction

In the summer of 1998, a large outbreak of Escherichia coli O157:H7 infections occurred in Alpine, Wyoming. We identified 157 ill persons; stool from 71 (45%) yielded E. coli O157:H7. In two cohort studies, illness was significantly associated with drinking municipal water (town residents: adjusted odds ratio=10.1, 95% confidence intervals [CI]=1.8-56.4; visitors attending family reunion: relative risk=9.0, 95% CI=1.3-63.3). The unchlorinated water supply had microbiologic evidence of fecal organisms and the potential for chronic contamination with surface water. Among persons exposed to water, the attack rate was significantly lower in town residents than in visitors (23% vs. 50%, p<0.01) and decreased with increasing age. The lower attack rate among exposed residents, especially adults, is consistent with the acquisition of partial immunity following long-term exposure. Serologic data, although limited, may support this finding. Contamination of small, unprotected water systems may be an increasing public health risk.

Escherichia coli O157:H7 is now a well-recognized cause of human illness. Although outbreaks of E. coli O157:H7 infections are frequently associated with food or milk derived from cattle, other sources, including fresh fruits and vegetables and water, have been implicated [1]. In the United States, the first reported drinking water outbreak of E. coli O157:H7 infections occurred in 1989 in rural Missouri [2]. Since this outbreak, six others have been associated with drinking water. Three were small and occurred in a camp, a recreational vehicle park, and a well (Centers for Disease Control and Prevention [CDC], unpub. data). More recently, three highly publicized drinking water outbreaks of E. coli O157:H7 infections (one each in Wyoming, New York, and Canada), have focused increased attention on the safety of drinking water [3,4]. Here we summarize the results of the outbreak investigation in Wyoming.

During late June 1998, physicians near Alpine, Wyoming, noted an increase in bloody diarrhea among town residents. Alpine is a small town (pop. <500) on the Wyoming-Idaho border that is frequented by tourists to Grand Teton and Yellowstone National Parks. By July 9, E. coli O157:H7 had been isolated from stool samples from 14 persons, including residents of Wyoming, Utah, and Washington. On July 11, CDC and Wyoming health officials began an investigation to determine the magnitude of the outbreak and the source of E. coli O157:H7 infections.


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