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National Surveillance Team - Enteric Diseases Epidemiology Branch

Shiga Toxin-Producing Escherichia coli (STEC) Case Surveillance

Shiga toxin-producing Escherichia coli (STEC) causes diarrhea and hemolytic uremic syndrome (HUS).  The STEC serotype that causes most outbreaks and most cases of HUS in the United States is E. coli O157:H7.  Non-O157 STEC strains have caused several U.S. outbreaks and can be isolated from diarrheal stools in similar frequency as E. coli O157:H7. 

In June 2000, the Council of State and Territorial Epidemiologists (CSTE) passed a position statement recommending inclusion of E. coli O157 and non-O157 STEC that cause human illness as notifiable to the Nationally Notifiable Diseases Surveillance System (NNDSS).  Reporting of non-O157 STEC has increased every year since implementation in 2001.  

Identification of a STEC requires demonstrating the ability of the E. coli isolate to produce Shiga toxin.  Because virtually all E. coli O157:H7 strains produce Shiga toxin, identification of both the O and H antigens of this serotype is sufficient to consider it a STEC.  Before 1995 Shiga toxin was detected by using highly technical assays available only at reference and research laboratories.  Since 1995, the Food and Drug Administration (FDA) has licensed several rapid enzyme immunoassays (EIA) for the detection of Shiga toxin.  The assays are highly sensitive and specific when used on broth cultures of human stool specimens.  Since these EIA kits have become commercially available and the use of polymerase chain reaction (PCR) to identity toxin genes has also increased, the number of non-O157 STEC isolates sent to CDC for serotyping has increased each year.

Healthcare providers should notify clinical diagnostic laboratories when STEC O157 infection is suspected so that appropriate testing methods can be applied.  Clinical laboratories should strongly consider including STEC O157 in their routine bacterial enteric panel (with Salmonella, Shigella, and Campylobacter.)  The best way to identify all STEC infections is to screen all stool samples submitted for routine enteric bacterial testing for Shiga toxins using EIA or PCR.  Ideally, the clinical diagnostic laboratory should culture simultaneously for STEC O157 (e.g., on a sorbitol-containing medium such as sorbitol MacConkey agar).  Clinical diagnostic laboratories that use a Shiga toxin EIA but do not perform simultaneous culture for STEC O157 should culture all Shiga toxin-positive broths for STEC O157 as soon as possible and forward these isolates to a state or local public health laboratory for confirmation and subtyping.  When a Shiga toxin-positive broth does not yield STEC O157, broth culture should be forwarded to the state or local public health laboratory for identification of non-O157 STEC.  State and local public health laboratories should confirm the presence of Shiga toxin in broths and should attempt to obtain a STEC isolate.  All non-O157 STEC isolates should be sent by public health laboratories to CDC for confirmation and further characterization.

Data sources for STEC surveillance include: 1) laboratory-confirmed cases in the NNDSS; 2) the Public Health Laboratory Information System (PHLIS); and 3) isolates received by CDC’s National Escherichia coli Reference Laboratory.  An annual summary of cases of non-O157 reported to CDC can be found within the Bacterial Foodborne and Diarrheal Disease National Case Surveillance, Annual Report.

Additional information on STEC can be found on the Foodborne Diseases Active Surveillance Network (FoodNet) site.

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