Academic journal article Journal of Environmental Health

A Beach-Associated Outbreak of Escherichia Coli O157:H7

Academic journal article Journal of Environmental Health

A Beach-Associated Outbreak of Escherichia Coli O157:H7

Article excerpt

Introduction

Each year approximately 20,000 people in the United States become ill from exposure to Escherichia coli O157:H7; some develop hemolytic uremic syndrome (HUS) (1-3). Most outbreaks are associated with eating contaminated food, whereas waterborne outbreaks are rarely reported. In July 1995, the Illinois Department of Public Health (IDPH) investigated an outbreak in which 12 children who had gone swimming at a bathing beach in Rock Cut State Park in northern Illinois became ill with E. coli O157:H7 infections. The beach was closed on July 6, 1995, and, since E. coli has been reported to survive in lake water for weeks or months, the beach remained closed for the remainder of the summer (4).

Methods and Results

Cases

On July 5, 1995, Winnebago County Health Department reported an initial cluster of six E. coli O157:H7 cases, five of which were children. Four of the children were from Rockford, Illinois, and one child was a resident of Wisconsin. The sixth case, an adult, was a resident of Freeport, Illinois. This case was later determined to be unrelated to the lake cases. Interviews with the children's parents revealed no common food source, but all of the children had visited Rock Cut State Park on June 24 or 25. The park contains a lake swimming beach operated by the Illinois Department of Natural Resources (DNR).

A case was defined as a resident of or a visitor to the Rockford area who had at least one of the following in the week from June 25 through July 1:

* bloody diarrhea,

* HUS,

* serologic E. coli O157:H7 confirmation by the Centers for Disease Control and Prevention (CDC), or

* culture-confirmed E. coli O157:H7 and pulse field gel electrophoresis (PFGE) pattern consistent with lake-associated cases.

Additional cases were identified through active surveillance in clinical laboratories, from citizen calls following media coverage, and by asking cases if they knew of any additional ill people. Twelve children (including the initial five) met the case definition. Seven stool isolates of E. coli O157:H7 were sent to CDC to test for shiga-like toxin and for PFGE. All stool isolates that came from cases visiting Rock Cut State Park (n = 6) had identical PFGE patterns, and all six isolates produced Type I and Type II shiga-like toxins. The stool isolate from the Freeport adult had a different PFGE pattern. Serum samples from individuals with no positive stool cultures but with symptoms suggestive of E. coli O157:H7 infection were sent to CDC for antibody titer testing.

Of the 12 cases, seven were culture confirmed as having E. coli O157:H7 infections; one had HUS and was culture-confirmed as having an E. coli O157 infection, but H typing was not performed; three had positive serology; and one had bloody diarrhea without being culture-confirmed. Cases from whom stool cultures were obtained (n = 8) were negative for Salmonella, Shigella, and Campylobacter. Two families each had two children affected with E. coli O157:H7. Eight children were from two to six years of age, and four were from seven to 12 years of age. Seven children were males.

The incubation period for the cases ranged from three hours to seven days with a mean of 3.7 days [ILLUSTRATION FOR FIGURE 1 OMITTED]. One child who swam on Saturday (June 24) experienced symptoms three hours after swimming. The symptoms lasted 36 hours and recurred seven days after swimming. Nine of the children experienced bloody diarrhea. Three of the children (two, four, and five years of age) developed HUS and were hospitalized for a minimum of one month. The attack rate for illness in 4,700 lake swimmers on June 24 and June 25 was 0.25 percent. The identification of cases was enhanced by intense media coverage in the Rockford area. All 12 cases had swum at the lake.

Environmental Investigation

The park contains two connected, manmade lakes. The lake with the bathing beach is fed by a stream; an outflow (spillway) connects it to the second lake, where swimming is not permitted. …

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