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Multistate Outbreak of Escherichia coli O157:H7 Infections Associated with Eating Ground Beef --- United States, June--July 2002

During July 2002, the Colorado Department of Public Health and Environment (CDPHE) identified an outbreak of Escherichia coli O157:H7 infections among Colorado residents. This report summarizes the results of an ongoing epidemiologic and laboratory investigation that has linked 28 illnesses in Colorado and six other states to eating contaminated ground beef products recalled by ConAgra Beef Company on June 30, 2002. To date, seven patients have been hospitalized; five developed hemolytic-uremic syndrome (HUS).

For this investigation, a case was defined as culture-confirmed E. coli O157 infection in a Colorado resident with symptom onset on or after June 1, and an isolate matching the outbreak pulsed-field gel electrophoresis (PFGE) pattern by two-enzyme analysis. To date, 18 cases have been identified. The median age of patients was 15 years (range: 1--72 years). Dates of symptom onset ranged from June 13 to July 7. Two cases of HUS have been diagnosed among Colorado residents who have epidemiologic links to the outbreak but do not have laboratory-confirmed E. coli O157 infection.

Interviews with 16 of 18 patients with confirmed infection revealed that all ate ground beef during the 7 days before illness. All 16 patients ate ground beef that was purchased at grocery chain A during June 10--24. E. coli O157 was cultured from an opened package of ground beef collected from a patient's home. A traceback by CDPHE of ground beef collected from a patient's home indicated that it was reground by grocery chain A with meat produced on May 31 by ConAgra Beef Company. On June 30, independent of the outbreak investigation, ConAgra Beef Company issued a nationwide recall of 354,200 lbs of ground beef products produced on May 31. This recall was based on the detection of E. coli O157 during routine microbiologic testing conducted by the U.S. Department of Agriculture (USDA).

PFGE analysis conducted by CDPHE and CDC using two restriction enzymes indicated that the 18 outbreak-related human isolates of E. coli O157 from Colorado were indistinguishable from isolates of E. coli O157 recovered from the opened ground beef package from a patient's home and from the ConAgra Beef Company recalled ground beef product. To identify potential cases outside Colorado, the outbreak-related PFGE patterns were posted on PulseNet, the National Molecular Subtyping Network for Foodborne Disease Surveillance. On the basis of epidemiologic data and molecular subtyping, eight additional E. coli O157 cases related to the Colorado cluster have been identified in six states (California, Iowa, Michigan, South Dakota, Washington, and Wyoming). The dates of onset ranged from June 17 to 27. Of the eight patients outside Colorado, six had PFGE patterns that were indistinguishable from the outbreak pattern by two-enzyme analysis, and two were siblings of a PFGE-matched patient. State and local health departments are investigating additional cases to establish epidemiologic and molecular links to the outbreak.

Subsequent to the detection of this multistate outbreak and the initiation of an in-plant inspection of the ConAgra Beef Company by USDA, the nationwide recall of 354,200 lbs of ground beef was expanded to a nationwide recall of 18.6 million lbs of fresh and frozen ground beef and beef trimmings. The expanded recall included fresh and frozen ground beef products produced during April 12--June 29, and beef trimmings produced during April 12--July 11.

Reported by: P Shillam, MSPH, A Woo-Ming, Colorado Dept of Public Health and Environment. L Mascola, MD, R Bagby, Acute Communicable Disease Control Unit, Los Angeles County Dept of Health Svcs, Los Angeles, California. C Lohff, MD, Iowa Dept of Public Health. S Bidol, MPH, MG Stobierski, DVM, Michigan Dept of Community Health. C Carlson, MS, L Schaefer, L Kightlinger, PhD, South Dakota Dept of Health. S Seys, MPH, Wyoming Dept of Health. K Kubota, MPH, PS Mead, MD, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; P Kalluri, MD, EIS Officer, CDC.

Editorial Note:

E. coli O157:H7 was first described as a cause of human illness and associated with undercooked ground beef in 1982 (1). Symptoms of E. coli O157 infection include bloody and nonbloody diarrhea, vomiting, and abdominal cramps. Illness resolves typically within 7--10 days. A subset of patients, particularly the young and the elderly, will develop HUS, characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. Infection with E. coli O157 has been associated with exposure to contaminated food and water, person-to-person transmission, and contact with animal reservoirs (2). Foods of bovine origin, particularly ground beef, are common causes of sporadic infections and outbreaks of E. coli O157 (2,3). Surveys conducted on feed lots demonstrate that cattle can be infected symptomatically with E. coli O157, and the prevalence of E. coli O157 in feed lots can reach 63%--100%, particularly during the summer, under muddy conditions, or with feeding of barley (4,5).

Although the investigation is ongoing, the findings indicate that this outbreak is associated with the ConAgra Beef Company's recalled ground beef products. Supportive evidence includes 1) reported eating by all Colorado patients of ground beef purchased at grocery chain A; 2) recovery of E. coli O157 from leftover meat from a patient's home; 3) traceback of the leftover meat indicating that it was produced at grocery chain A using recalled meat; and 4) PFGE results demonstrating a unique strain of E. coli O157 in human isolates, leftover meat, and meat recalled from ConAgra Beef Company.

This outbreak demonstrates the continuing importance of routine public health surveillance combined with molecular subtyping in epidemiologic investigations. The PulseNet database includes molecular fingerprinting patterns of at least 9,800 isolates submitted since 1996. The PFGE pattern of the human and meat isolates in this outbreak was novel in the PulseNet database, facilitating the detection and investigation of seemingly sporadic cases of E. coli O157 infection in Colorado and six other states and strengthening the association between the recalled beef products and human illness.

The June 30 recall of meat occurred before detection of the multistate cluster of human infections and was based on results of microbiologic testing conducted by USDA. The subsequent identification of human illness associated with the recalled meat reinforces the importance to public health of microbiologic testing in meat processing plants.

The expanded recall announced on July 19 was one of the largest in U.S. history (6). Detailed information on the distribution of recalled meat is not available. The extent to which the recalled meat was repackaged and distributed under other labels is unclear, potentially making it difficult to identify the affected lots by simple inspection of the package. Grocers and butchers from whom ground beef was purchased might be able to advise concerned customers about the producer and production date of purchased meat. However, consumers should be aware that microbiologic testing in meat processing plants cannot eliminate the risk for contamination of ground beef with E. coli O157 and other pathogens. To further reduce the risk for illness, consumers can buy ground beef that is precooked or treated with electron beams. Consumers also can protect themselves by using safe food preparation practices. Frozen ground beef should be thawed in the refrigerator rather than at room temperature. Ground beef should be cooked thoroughly to internal temperatures of at least 160º F (71º C). Using meat thermometers will help ensure that internal temperatures are high enough to kill bacteria. To reduce the risk for cross-contamination, consumers should use soap and hot water to wash hands, utensils, and other surfaces that might have come into contact with raw or undercooked ground beef and other meat products. Additional food safety and product recall information is available from USDA at http://www.usda.gov; telephone 866-849-7438.

Acknowledgments

This report is based on data contributed by L Dippold, REHS, N Haubert, REHS, Tri-county Health Dept, Englewood; K Gieseker, PhD, J Beebe, PhD, S Burnite, Colorado Dept of Public Health and Environment. E Lehnkering, MS, Public Health Laboratory; T Lau, Environmental Health Svcs; R Reporter, MD, Acute Communicable Disease Control Unit, Los Angeles Dept of Health Svcs, Los Angeles; J Farrar, DVM, California Dept of Health Svcs. G Stoltman, PhD, M Boulton, MD, Michigan Dept of Community Health. Spokane Regional Health District, Washington State Dept of Health. A Heryford, MS, W Manley, MS, J Walford, Wyoming Dept of Health. M Lambert-Fair, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

References

  1. Riley LW, Remis RS, Helgerson SD, et al. Hemorrhagic colitis associated with a rare Escherichia coli serotype. N Engl J Med 1983;308:681--5.
  2. Griffin P, Mead P, Sivapalasingam S. Escherichia coli O157:H7 and other enterohemorrhagic E. coli, In: M Blaser, ed. Infections of the gastrointestinal tract. NEw York, New York: Lippincott Williams & Wilkins, 2002.
  3. Slutsker L, Ries AA, Maloney K, Wells J, Greene K, Griffin PM. A nationwide case-control study of Esherichia coli 0157:H7 infection in the United States. J Infect Dis 1998;177:962--6.
  4. Smith D, Blackford M, Younts S, et al., Ecological relationships between the prevalence of cattle shedding Escherichia coli O157:H7 and characteristics of the cattle or conditions of the feedlot pen. J Food Prot 2001;64:1899--903.
  5. Dargatz D, Wells SJ, Thomas LA, et al. Factors associated with the presence of Escherichia coli O157 in feces of feedlot cattle. J Food Prot 1997;60:466--70.
  6. CDC. Escherichia coli O157:H7 infections associated with eating a nationally distributed commercial brand of frozen ground beef patties and burgers---Colorado, 1997. MMWR 1997;46:777--8.

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