Resources for Clinicians and Laboratories

Guidance to Healthcare Providers and Clinical Laboratories

Antibiotics are not recommended for patients with suspected STEC infections until complete diagnostic testing can be performed and STEC infection is ruled out. Some studies have shown that administering antibiotics to patients with STEC infections might increase their risk of developing HUS, and a benefit of treatment has not been clearly demonstrated. Features of HUS include low platelet count, anemia due to broken blood cells, and kidney failure.

Many non-O157 STEC infections are not diagnosed. Patients with more severe illness are generally more likely to seek medical care and to have stool specimens tested to determine the cause of illness. Non-O157 STEC are a diverse group of bacteria that vary in virulence. There are two general types of Shiga toxins, Shiga toxin 1 and Shiga toxin 2. Strains may carry one Shiga toxin or both at the same time. Strains that produce Shiga toxin 2 tend to be more virulent. Even among the more virulent STEC strains, many infections go undiagnosed.

Guidelines to ensure as complete as possible detection and characterization of STEC infections include the following:

  • All stools submitted for testing from patients with acute community-acquired diarrhea should be cultured for STEC O157. These stools should be simultaneously assayed for non-O157 STEC with a test that detects Shiga toxins or the genes encoding these toxins.
  • Clinical laboratories should report and send E. coli O157 isolates and Shiga toxin-positive samples to state or local public health laboratories as soon as possible for additional characterization.
  • Specimens or enrichment broths in which Shiga toxin or STEC are detected, but from which O157 STEC are not recovered should be forwarded as soon as possible to a state or local public health laboratory so that non-O157 STEC can be isolated.
  • Often, by the time a patient presents with HUS, the causative STEC can no longer be easily isolated from a stool specimen. For any patient with HUS without a culture-confirmed STEC infection, stool can be sent to a public health laboratory or to CDC through their public health laboraotory for immunomagnetic separation (IMS) techniques that can increase the sensitivity of culture. In addition, with prior approval, serum can be sent through a state public health laboratory to CDC for serological testing for antibodies to some STEC serogroups.

The benefits of adhering to the recommended testing strategy include early diagnosis, improved patient outcome, and detection of infections caused by all STEC serotypes.

All patients with Shiga toxin-positive diarrheal illness or HUS should be reported to health departments.