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Enhanced Detection of Sporadic Escherichia coli O157:H7 Infections -- New Jersey, July 1994

Infection with Escherichia coli O157:H7 causes an estimated 20,000 cases of diarrhea in the United States each year. Although E. coli O157:H7 can be isolated using commercially available media, many clinical laboratories do not routinely test stool samples for the organism. In 1993, the Council of State and Territorial Epidemiologists recommended that clinical laboratories begin culturing all bloody stools -- and optimally all diarrheal stools -- for E. coli O157:H7 (1). This report describes the investigation of a pseudo-outbreak of E. coli O157:H7 infection that occurred in New Jersey during July 1994 after a year-long increase in the number of laboratories culturing all diarrheal specimens for this pathogen.

From June 1 through July 27, 1994, a total of 46 culture-confirmed cases of E. coli O157:H7 infection were reported to the New Jersey Department of Health (NJDOH). In comparison, five cases had been reported during the same period in 1993. To identify the source of these infections, NJDOH and CDC conducted a case-control study involving 23 cases and 46 age-matched controls. A case was defined as a stool culture positive for E. coli O157:H7 in a New Jersey resident with onset of diarrhea during July 1994. Of 22 case-patients for whom data were available, 18 (81%) reported they had eaten a hamburger during the week before illness, compared with 21 (47%) of 45 matched controls for whom data were available (matched odds ratio=undefined, p less than 0.001). Of the hamburgers eaten by case-patients, 73% had been prepared at home or at picnics. No other food item or activity was associated with illness.

An extensive traceback investigation was conducted to identify the source of ground beef eaten by ill persons. The investigation identified multiple retail and wholesale sources, suggesting these cases were sporadic and not related to a common-source outbreak. This finding was verified by laboratory tests that identified 17 different strains of E. coli O157:H7 among the 23 clinical isolates. To assess the role of enhanced laboratory surveillance in generating the increase in case reports, NJDOH surveyed 20 clinical laboratories that had reported at least one E. coli O157:H7 isolate during 1994. The number of laboratories culturing all diarrheal specimens for E. coli O157:H7 had increased from two (10%) in July 1993 to 18 (90%) in July 1994. Reported by: L Finelli, DrPh, E Crayne, E Dalley, MA, K Pilot, KC Spitalny, MD, State Epidemiologist, New Jersey Dept of Health. Food Safety Inspection Svc, US Dept of Agriculture. Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Since 1993, several outbreaks of E. coli O157:H7 infection have been detected as a result of increased laboratory testing for this organism (2,3). The findings in New Jersey demonstrate that increased testing can also substantially enhance detection and reporting of sporadic infections. In January 1995, an estimated 29% of clinical laboratories in the United States were culturing all diarrheal specimens for E. coli O157:H7; however, the proportion was increasing rapidly (CDC, unpublished data, 1995). Therefore, public health officials should anticipate continuing increases in reports of both sporadic and outbreak-related cases and should evaluate the role of enhanced detection when an outbreak is suspected.

A primary strategy for preventing infection with E. coli O157:H7 is reducing risk behaviors through consumer education. In New Jersey, the sudden increase in E. coli O157:H7 case reports was reported widely by the news media. The press coverage provided public health officials with an opportunity to inform the public about the risks of eating undercooked ground beef, the need for safe food-handling practices, and the potential for person-to-person transmission.

Although traceback investigations can be important in preventing E. coli O157:H7 infections, they should be undertaken selectively. Traceback investigations are most useful when the implicated vehicle is novel (e.g., salami) (3) or has a long shelf life (e.g., frozen hamburger patties) (4). Because fresh ground beef has a short shelf life and usually is derived from many sources, traceback investigations involving this food item are often unproductive.

An effective public health response to E. coli O157:H7 requires a timely and sensitive national surveillance system. Through March 1995, a total of 33 states had enacted legislation designating E. coli O157:H7 infection as a reportable disease (W. Keene, State Health Division, Oregon Department of Human Resources, personal communication, 1995). In addition, CDC has developed a software module that enables states to report laboratory-confirmed cases to CDC through the Public Health Laboratory Information System (PHLIS). During January 1994-March 1995, a total of 38 states reported to PHLIS 1187 isolates of E. coli that were positive for both the O157 and H7 antigens. Although PHLIS is a passive, laboratory-based system, reported incidence rates in some states have exceeded three cases per 100,000 population. With expanded culturing by clinical laboratories and strengthened reporting by states, these rates probably will increase.

References

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

  2. CDC. Laboratory screening for Escherichia coli O157:H7 -- Connecticut, 1993. MMWR 1994; 43:192-4.

  3. CDC. Escherichia coli O157:H7 outbreak linked to commercially distributed dry-cured salami -- Washington and California, 1994. MMWR 1995;44:157-60.

  4. Bell BP, Goldoft M, Griffin PM, et al. A multistate outbreak of Escherichia coli O157:H7-associated bloody diarrhea and hemolytic uremic syndrome from hamburgers: the Washington experience. JAMA 1994;272:1349-53.




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