Chapter 13-10: Shiga toxin–producing E coli (STEC)

TEXTBOOK PRESENTATION

STEC usually presents with diarrhea and abdominal pain. The pain is often worse in the right lower quadrant. Bloody diarrhea is very common, while nausea, vomiting, and fever are not.

DISEASE HIGHLIGHTS

1. Nomenclature

   1. STEC is a strain of E coli that produces Shiga toxin.

   2. STEC is also called enterohemorrhagic E coli (EHEC).

   3. The most common strain of STEC in the United States is O157:H7.

   4. Other than STEC, there are 4 types of E coli that cause diarrheal illness in adults.

      1. Enterotoxigenic E coli (ETEC) is a common cause of travelers’ diarrhea that causes symptoms through elaboration of a toxin.

      2. Enteropathogenic E coli (EPEC) is a common cause of watery diarrhea in adults and children.

      3. Enteroinvasive E coli (EIEC) causes bloody diarrhea with tenesmus similar to Shigella.

      4. Enteroaggregative E coli (EAEC) is a common cause of diarrhea in children and travelers’ diarrhea.

2. STEC is most commonly associated with undercooked beef, but it can also be found in fecally contaminated food products such as produce, fruit products, and dairy products.

3. STEC can also be transmitted by direct contact with infected people and livestock.

4. Symptoms of STEC include bloody diarrhea, abdominal pain, and absence of fever.

5. STEC can cause hemolytic uremic syndrome (HUS), a condition that is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury.

EVIDENCE-BASED DIAGNOSIS

1. Patients infected with STEC are significantly more likely than patients infected with other pathogens to:

   1. Report bloody diarrhea and provide visibly bloody specimens

   2. Lack fever

   3. Have abdominal tenderness

   4. Have a white blood cell count > 10,000/mcL

2. Positive culture for STEC, detection of Shiga toxin by immunoassay, or detection of Shiga toxin gene by nucleic acid amplification testing is considered diagnostic.

   1. Selective culture media for STEC is required for growth.

   2. Multipathogen molecular testing panels have demonstrated high sensitivity (91-100%) and specificity (97–100%) for STEC.

3. Some microbiology laboratories perform testing for STEC with routine stool testing, but culture and toxin testing for STEC may need to be specifically requested in other microbiology laboratories.

TREATMENT

1. Treatment of STEC is controversial.

2. Antibiotics have demonstrated mixed results in studies, but there is a concern for increased risk of HUS with their use.