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Escherichia coli O157:H7 Outbreak Linked to Commercially Distributed Dry-Cured Salami -- Washington and California, 1994

From November 16 through December 21, 1994, a total of 20 laboratory-confirmed cases of diarrhea caused by Escherichia coli O157:H7 were reported to the Seattle-King County Department of Public Health (SKCDPH). In comparison, three cases were reported during October 1994. Epidemiologic investigation linked E. coli O157:H7 infection with consumption of a commercial dry-cured salami product distributed in several western states. Three additional cases subsequently were identified in northern California. This report summarizes preliminary findings from the outbreak investigation. Washington

Infection with E. coli O157:H7 has been a reportable disease in Washington since 1987; cases are identified through routine follow-up of infections reported from local laboratories to the SKCDPH. Among the 20 case-patients, the median age was 6 years (range: 23 months to 77 years), 11 (55%) were male, and all resided in King County. Three patients required hospitalization, including a 2-year-old who developed hemolytic uremic syndrome (HUS).

Interviews with initial patients suggested that brand A dry-cured salami purchased at a local grocery chain was associated with illness. Based on these preliminary findings, during November 23-25, the grocery chain voluntarily withdrew brand A salami from its King County stores. To assess potential risk factors for infection, the SKCDPH conducted a case-control study of 16 cases and age-matched controls. A case was defined as culture-confirmed E. coli O157:H7 in a King County resident with onset of illness during November 15-29. Eleven (68%) case-patients and one (6%) control reported eating brand A dry-cured salami within 7 days before onset of illness (Mantel-Haenszel matched odds ratio=undefined; p less than 0.01). No other food item was significantly associated with infection.

All salami was purchased from the delicatessen counters of the local grocery chain. On November 28 and 29, environmental investigations were conducted at three of these delicatessens, and food samples were collected. No errors in food-handling practices were identified. E. coli O157:H7 was isolated from samples of brand A presliced dry-cured salami from two of the delicatessens on December 2 and subsequently from a sample from a third delicatessen in the grocery chain. On December 2, the SKCDPH issued a press release informing the public of this problem and notified the U.S. Department of Agriculture (USDA). On December 6, the manufacturing company voluntarily recalled 10,000 pounds of implicated product labeled "Sell by May 7, 1995," which had been distributed in California, Oregon, and Washington. In addition, the company requested that their distributors suspend the sale of all of its products until the source of contamination was determined. The last case-patient had onset of illness on December 6.

Restriction fragment length polymorphism (Shiga-like toxin RFLP and lambda-RFLP) analysis by the University of Washington School of Public Health and Community Medicine determined that patterns were identical in 15 of 19 clinical isolates and in the three salami isolates. Sources for the matching isolates included 12 patients who ate salami, two secondary cases, and one person who ate sliced turkey purchased from a delicatessen where brand A dry-cured salami was sold, suggesting possible cross-contamination. The four nonmatching isolates were from specimens from patients who did not eat salami. These findings were confirmed at CDC by pulsed-field gel electrophoresis on a sample of outbreak-related isolates. California

Three patients with laboratory-confirmed E. coli O157:H7 infection who reported consumption of brand A salami during the week before illness onset were hospitalized in northern California during November. Two patients resided in Sonoma County and one in Sacramento County. Patients were aged 4, 25, and 71 years; the 4-year-old developed HUS. Dates of onset ranged from November 17 through November 27. In addition, a 20-month-old resident of Sacramento who had consumed brand A dry-cured salami before onset of illness was hospitalized with postdiarrheal HUS on November 24. Although cultures of stool from this patient were negative for routine bacterial pathogens, screening for E. coli O157:H7 had not been performed before institution of antibiotic therapy. However, serum antibody to O157 antigen subsequently was detected at the Microbial Diseases Laboratory of the California State Department of Health Services (CSDHS).

CSDHS subsequently cultured E. coli O157:H7 from two samples of presliced brand A dry-cured salami obtained from stores in California. Reported by: ER Alexander, MD, J Boase, MSN, M Davis, DVM, L Kirchner, C Osaki, MSPH, T Tanino, Seattle-King County Dept of Public Health, M Samadpour, PhD, Univ of Washington, P Tarr, MD, Children's Hospital and Medical Center, Seattle; M Goldoft, MD, S Lankford, J Kobyashi, MD, P Stehr-Green, DrPH, State Epidemiologist, Washington Dept of Health. P Bradley, B Hinton, MD, Sacramento County Health Dept, Sacramento; P Tighe, B Pearson, GR Flores, MD, Sonoma County Health Dept, Santa Rosa; S Abbott, R Bryant, SB Werner, MD, DJ Vugia, MD, State Epidemiologist, California State Dept of Health Svcs. Food Safety Inspection Svc, US Dept of Agriculture. Div of Training, Epidemiology Program Office; Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: E. coli O157:H7 was first recognized as a human pathogen in 1982 (1) and is now an important cause of bloody diarrhea and a leading cause of acute renal failure in children (2). Each year in the United States, E. coli O157:H7 infection accounts for a minimum 20,000 cases of illness and 250 deaths (CDC, unpublished data, 1995). In 1993, the Council of State and Territorial Epidemiologists recommended that E. coli O157:H7 be a nationally reportable disease and that clinical laboratories screen at least all bloody stools for this pathogen (3). In response to increased culturing, during 1993-1994, a total of 46 clusters of E. coli O157:H7 infections involving an estimated 1300 persons were recognized in the United States. The outbreak described in this report highlights the critical role of both microbiologic surveillance for E. coli O157:H7 on diarrheal stool specimens submitted for bacterial culture and a reporting system to detect evolving communitywide outbreaks (4,5). As of January 1995, 32 states required that E. coli O157:H7 isolates be reported to the state health department, and an additional 16 states were considering establishing this requirement (CDC, unpublished data, 1995).

The identification of dry-cured salami as a source of E. coli O157:H7 infection in this outbreak extends the spectrum of food vehicles associated with this organism. Previous outbreaks have been associated with other foods of animal origin -- including ground beef, roast beef, and raw milk (2) -- and raw vegetables and apple cider possibly contaminated with cow feces (6,7). Dry-cured salami is not cooked but is usually produced through fermentation followed by drying. Specific manufacturing processes may vary among companies and for different types of salami. Experimental inoculation of a salami batter with E. coli O157:H7 has demonstrated that the organism survives but does not grow during fermentation, drying, and storage for 2 months at 39.2 F (4 C) (8).

On December 9, representatives of the USDA's Food Safety Inspection Service (FSIS) and 250 dry-sausage makers met to address the isolation of E. coli O157:H7 from this product. Industry representatives agreed to evaluate their production methods to assess the survival of E. coli O157:H7. FSIS will review industry findings and initiate any necessary changes in manufacturing processes (e.g., fermentation or time and temperature procedures).

The investigation in this report illustrates the usefulness of molecular subtyping techniques to distinguish outbreak strains of E. coli O157:H7 from others circulating in the community. Subtyping methods have included RFLP, pulsed-field gel electrophoresis, and phage typing (9,10). The combined use of methods may assist efforts to determine the relatedness of strains and assess epidemiologic associations (10). Prospective subtyping of E. coli O157:H7 strains may be used as an adjunct to microbiologic surveillance to detect clusters of related cases, guide interviewing, ascertain the source of infection, and prevent additional cases.

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 PM, Tauxe RV. The epidemiology of infections caused by Escherichia coli O157:H7, other enterohemorrhagic E. coli, and the associated hemolytic uremic syndrome. Epidemiol Rev 1991;13:60-98.

  3. Council of State and Territorial Epidemiologists. CSTE position statement #4: national surveillance of Escherichia coli O157:H7. Atlanta: Council of State and Territorial Epidemiologists, June 1993.

  4. Alexander ER. Editorial response: surveillance of Escherichia coli O157:H7 -- a necessity for the prevention of an emerging infectious disease {Editorial}. Clin Infect Dis 1994;19:844-5.

  5. Tarr PI. "4+ Normal flora" (or is it?) {Editorial}. J Pediatr Gastroenterol Nutr 1994;19:145-7.

  6. Cieslak P, Barrett T, Griffin P. Escherichia coli O157:H7 infection from a manured garden. Lancet 1993;342:367.

  7. Besser RE, Lett SM, Weber TJ, et al. An outbreak of diarrhea and hemolytic uremic syndrome from Escherichia coli O157:H7 in fresh-pressed apple cider. JAMA 1993;269:2217-20.

  8. Glass KA, Loeffelholz JM, Ford JP, Doyle MP. Fate of Escherichia coli O157:H7 as affected by pH or sodium chloride in fermented, dry sausage. Appl Environ Microbiol 1992;58:2513-6.

  9. Samadpour M, Grimm LM, Desai B, Alfi D, Ongerth JE, Tarr PI. Molecular epidemiology of Escherichia coli O157:H7 strains by bacteriophage restriction fragment length polymorphism analysis: application to a multistate foodborne outbreak and day-care center cluster. J Clin Microbiol 1993;31:3179-83.

  10. Barrett TJ, Lior H, Green JH, et al. Laboratory investigation of a multistate food-borne outbreak of Escherichia coli O157:H7 by using pulsed-field gel electrophoresis and phage typing. J Clin Microbiol 1994;32:3013-7.




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