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Emerging Infectious Diseases Laboratory Screening for Escherichia coli O157:H7 -- Connecticut, 1993

Escherichia coli O157:H7, first recognized as a pathogen in humans in 1982 (1), is a common cause of bloody diarrhea and a leading cause of acute renal failure in children. In June 1993, the Council of State and Territorial Epidemiologists (CSTE) recommended that clinical laboratories screen at least all bloody stools for E. coli O157:H7 using sorbitol-MacConkey medium (2). Following the CSTE issuance, in late June the Connecticut Department of Public Health and Addiction Services (DPHAS) mailed the same recommendation to all clinical laboratories in the state and encouraged laboratories to send suspected E. coli O157:H7 strains to the DPHAS laboratory for confirmation. To assess the impact of the DPHAS recommendations and to characterize the screening practices for E. coli O157:H7, in November 1993 DPHAS surveyed laboratories in Connecticut. This report presents the findings of the survey.

DPHAS mailed questionnaires to all 139 licensed clinical laboratories in Connecticut; laboratories that did not respond to the mailed questionnaire were contacted by telephone. The response rate for the survey was 100%.

Of the 139 laboratories, 44 (32%) performed on-site testing of stool specimens received directly from health-care providers or referred from other laboratories. Of these 44 laboratories, 19 (43%) screened all stool specimens for E. coli O157:H7, 21 (48%) screened only bloody stools, and four (9%) screened only at physician request.

Of the 44 laboratories that performed on-site testing of stool specimens, the number that cultured all stools or all bloody stools for E. coli O157:H7 increased from 11 (25%) in June 1993 to 40 (91%) in November 1993. Of the 29 laboratories that changed their policy to culture all stools or all bloody stools for E. coli O157:H7, 21 (72%) reported beginning in response to the DPHAS notification, four (14%) as a result of publicity associated with the E. coli outbreaks in the western United States in early 1993, two (7%) following the general meeting of the American Society of Microbiology in May 1993 where information on E. coli O157:H7 screening was presented, and two (7%) for a combination of these and other reasons.

Reported by: PA Mshar, ML Cartter, MD, JL Hadler, MD, State Epidemiologist, Connecticut Dept of Public Health and Addiction Svcs. Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: E. coli O157:H7 is not usually detected by the methods used to isolate and identify other bacterial enteric pathogens (1). Sorbitol-MacConkey medium and O157 antiserum, which are both readily available, should be used to identify the organism (1). Most outbreaks of illness caused by E. coli O157:H7 have been detected because of clusters of hemolytic uremic syndrome, thrombotic thrombocytopenic purpura, or severe diarrheal illness (1,3,4). In the absence of routine screening of diarrheal stool specimens for E. coli O157:H7, neither small outbreaks nor isolated cases in persons without severe illness are likely to be detected. Routine screening of stool specimens for E. coli O157:H7 may reduce the likelihood of unnecessary diagnostic procedures and treatments while permitting detection of outbreaks, timely initiation of public health intervention, and refined characterization of the epidemiology of this problem.

The findings in this report suggest that, in Connecticut, routine screening for E. coli O157:H7 resulted in an increase in the number of reported cases and contributed to the recognition of the first outbreak of E. coli O157:H7 infections in the state. Reporting of E. coli O157:H7 isolates by laboratories to DPHAS has been required since 1990. No cases were reported in 1990, one in 1991, 19 in 1992, and 50 in 1993, with a marked increase in reporting beginning in June 1993. In September 1993, an outbreak of O157 infections was detected following the isolation of the organism from four persons on the same day; the hospital laboratory involved had initiated a policy in June 1993 to screen all bloody stools for E. coli O157:H7.

The proportion of clinical laboratories in the United States that routinely screen at least bloody stools for E. coli O157:H7 is not well described. A recent survey in the San Francisco Bay area found that only eight (20%) of 41 laboratories performed such screening (CDC, unpublished data, 1994). Nationally, as of October 1993, 17 (34%) states required that E. coli O157:H7 isolates be reported to state health departments; 20 additional states are establishing such requirements (G. Birkhead, New York State Health Department, personal communication, March 14, 1994). The findings in this report suggest that a substantial proportion of laboratories would perform these screenings if encouraged by state health departments.

A CDC-developed video, "E. coli O157:H7 -- What the Clinical Microbiologist Should Know," provides a guide to the isolation and identification of E. coli O157:H7. This video is available from the Association of State and Territorial Public Health Laboratory Directors, 1211 Connecticut Avenue, NW, Suite 608, Washington, DC 20036; fax (202) 887-5098.


  1. 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.

  2. 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.

  3. Swerdlow DL, Woodruff BA, Brady RC, et al. A waterborne outbreak in Missouri of Escherichia coli O157:H7 associated with bloody diarrhea and death. Ann Intern Med 1992;117:812-9.

  4. Besser RE, Lett SM, Weber JT, 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.

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