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Epidemiologic Notes and Reports Foodborne Outbreak of Gastroenteritis Caused by Escherichia coli O157:H7 -- North Dakota, 1990
In late July and early August 1990, an outbreak of gastroenteritis occurred among persons who had eaten a meal while attending an agricultural threshing show in North Dakota on July 28-29. At least 70 (3.5%) of the more than 2000 attendees were affected; of these, 16 persons were hospitalized, and two children, aged 2 and 8 years, were diagnosed with hemolytic uremic syndrome. An epidemiologic investigation was conducted by the North Dakota State Department of Health and Consolidated Laboratories.
A case was defined as gastrointestinal illness in a person 2-5 days after eating at the threshing show. Of the 70 case-patients, 65 (93%) had diarrhea; 55 (79%), abdominal cramping; 27 (39%), bloody diarrhea; and 21 (30%), nausea. The mean age of case-patients was 38 years (range: 2-82 years); 36 (51%) were women. Onset of cases occurred from July 30 through August 2, with a peak (22 (31%) cases) on July 31. For those who reported having bloody diarrhea, the mean incubation period from the time the implicated meal was eaten on July 28 to onset of symptoms was 74.6 hours (range: 32.3-132.0 hours).
Stool samples obtained from 20 ill persons were analyzed by the Division of Microbiology of the North Dakota State Department of Health and Consolidated Laboratories. Escherichia coli, serotype O157:H7, was isolated from eight of the samples. The positive samples were collected during August 2-4, from 1 to 4 days after onset of symptoms; negative samples were obtained 4-20 days after onset of symptoms. Analysis by CDC confirmed the isolate results and detected both Shiga-like toxins I and II (verocytotoxin 1 and 2).
Analysis of food histories obtained from 157 persons implicated a buffet-style dinner on July 28. Although food samples were not available at the time of the investigation, food history analysis indicated that roast beef served at the dinner was the most likely source of infection (Table 1): ill persons were more likely to report having eaten rare roast beef (chi-square test for linear trend=5.4, p=0.02) and/or cool roast beef (chi-square test for linear trend=7.6, p=0.006).
Sixteen inside round roasts had been special-ordered from a local grocer for the dinner; none had been sold to local customers. Fourteen of the roasts were skewered on a noncommercial grade metal spit and rotated in a closed drum above a charcoal fire for approximately 10 hours; the temperature of some of the roasts reportedly registered 140 F (60 C). Two other roasts were prepared in enamel-lined electric roasting pans set to cook at 300 F (149 C) according to the temperature dials on the pans; no temperatures were recorded for these roasts.
All roasts were sliced and served from the electric roasting pans. During the serving period (approximately 5-8 p.m.), the pans were not cleaned but were refilled with slices from other roasts. Reported by: S McDonough, MD, Preventive Health Section; F Heer, Div of Disease Control; L Shireley, MPH, State Epidemiologist, North Dakota State Dept of Health and Consolidated Laboratories. Enteric Diseases Br, Div of Bacterial and Mycotic Diseases, Center for Infectious Diseases, CDC.
Editorial Note: Since E. coli O157:H7 was first reported as a cause of bloody diarrhea in 1982, infection with this pathogen has emerged as an important cause of both bloody and nonbloody diarrhea in the United States; in some cases, infection with this organism results in hemolytic uremic syndrome and thrombotic thrombocytopenic purpura (1-8). Young children and the elderly are at increased risk for these more severe complications (2,4,6,7).
Transmission of this organism has been documented through food (1,3-5); person-to-person contact (6,7); and, rarely, contaminated water (8). Foodborne outbreaks have been most commonly associated with undercooked ground beef; some sporadic cases have been associated with drinking unpasteurized milk. A reservoir in healthy dairy cattle has been documented (5,9).
The outbreak in North Dakota is the second instance in which roast beef has been implicated as the vehicle of transmission. Because thorough cooking kills E. coli O157:H7, cooking beef until a meat thermometer reads greater than or equal to 140 F (greater than or equal to 60 C) will reduce the risk for this infection. If cooked beef is to be kept hot, the holding temperature should be at least 140 F (60 C). Although the precise source of the outbreak in North Dakota is unknown, inadequate cooking and possible cross-contamination of cooked, sliced roast beef as a result of the food-preparation and serving techniques may have contributed to the outbreak.
In many clinical laboratories, testing for E. coli is not routinely done. The yield of cultures is likely to be highest when specimens are obtained within 6 days of onset of illness (10) in patients with grossly bloody diarrhea and abdominal cramps. A request for culture should specify sorbitol MacConkey agar; E. coli O157:H7 ferments sorbitol slowly and appears sorbitol-negative at 24 hours. Suspected sorbitol-negative colonies can be confirmed using commercial antiserum. Most state and territorial public health laboratories are able to confirm isolates.
The North Dakota State Department of Health and Consolidated Laboratories has made laboratory isolation of E. coli reportable and is conducting surveillance for this pathogen.
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