Clinical Pearls & Morning Reports
Published October 11, 2023
Shiga toxin–producing Escherichia coli (STEC) are bacteria that carry the genes that produce Shiga toxins. These pathogens have the potential to cause diarrhea, which is often bloody, and can trigger a thrombotic microangiopathy that leads to the hemolytic–uremic syndrome (HUS). STEC are responsible for most cases of HUS in children worldwide. Read the NEJM Review Article here.
Q: Describe some of the epidemiological features of STEC infections.
A: The incidence of STEC infection peaks during summer and fall and is greatest among children younger than 5 years of age, the group at highest risk for the development of HUS. Predominant STEC serogroups vary according to region. E. coli O157 is the most commonly identified serogroup in the stool of symptomatic persons worldwide. It is currently identified in 84% of HUS cases in the United States. The two Shiga toxin families, Shiga toxin 1 and Shiga toxin 2, have different clinical implications. Shiga toxin 2–producing serotypes are much more virulent than Shiga toxin 1–producing serotypes, which rarely lead to HUS unless they also produce Shiga toxin 2. Since E. coli O157 almost universally produce Shiga toxin 2, they are always assumed to be high-risk STEC.
Q: Is it important to send stool specimens for testing early in the course of a suspected STEC infection?
A: Early diagnosis of STEC infection is important for case management. Stool samples obtained from all patients with hematochezia and from children with nonbloody diarrhea accompanied by tenesmus or severe abdominal pain should be sent for bacterial pathogen detection. Because the ability to identify STEC in stool diminishes daily after the onset of diarrhea, sensitivity is optimized by prompt acquisition and submission of specimens for testing. Thus, if a specimen of bulk stool is not immediately available, a rectal swab specimen should be obtained and processed.
A: Multiple studies have shown an association between antibiotic administration and an increased risk of HUS among patients infected with high-risk STEC. Thus, avoiding empirical antibiotic administration in immunocompetent patients with bloody diarrhea is important. Although it is tempting to try to relieve abdominal pain, narcotics and antimotility drugs have been observed to prolong bloody diarrhea in E. coli O157 infection and to increase the risk of HUS and neurologic complications. Nonsteroidal antiinflammatory drugs can cause acute kidney injury during gastrointestinal infections and are best avoided.
A: The authors suggest daily laboratory testing to monitor all children infected with a known high-risk Shiga toxin (Shiga toxin 2 detected) or a suspected high-risk STEC (Shiga toxin detected but not genotyped in a patient with bloody diarrhea) until the window for the development of HUS has closed or repeat testing has revealed no evidence of a progressive microangiopathy. Rapidly progressive thrombocytopenia is the sentinel and universal hematologic abnormality in patients in whom HUS develops and is often accompanied by hemoglobinuria and elevated serum lactate dehydrogenase levels. Thus, laboratory testing should continue until the platelet count increases by at least 5% in specimens obtained 24 hours apart on or after the fifth day of illness in the context of improving or resolved gastrointestinal symptoms. Although HUS almost always manifests between days 5 and 14 of illness, microangiopathic changes are apparent by day 8 or 9, and anuria, if it occurs, rarely commences after day 10.