Shiga Toxin Escherichia coli Antigen, Feces
Rapid screening for EHEC serotypes including Escherichia coli O157:H7.
This test should serve as an adjunct to culture. However, in some situations when recovery of the organism by culture is not optimal (e.g. delayed transport of the specimen or transport of the specimen in preservative), or when isolation of the organism is not required for epidemiologic studies, this test may be considered as the preferred diagnostic method.
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Shiga toxin-producing Escherichia coli (STEC) have been recognized as agents of diarrhea and of sporadic cases and serious outbreaks of life-threatening hemorrhagic colitis and hemolytic uremic syndrome (HUS). Escherichia coli O157:H7 is the most frequently isolated enterohemorrhagic Escherichia coli (EHEC) serotype, but at least 50 serotypes have been implicated in the production of cytotoxins and development of complications.
Conventional testing methods for Escherichia coli O157: H7 involve isolation of the organism from fecal cultures followed by biochemical and immunologic confirmation. This method usually requires 72 hours for complete identification.
At this time, because antimicrobial therapy does not appear to be useful for treating the disease and may even increase the risk of HUS, recovery of Escherichia coli O157: H7 by culture for antimicrobial susceptibility testing is not necessary. The rapid diagnosis of Escherichia coli O157:H7 directly from fecal specimens is preferred to avoid unnecessary diagnostic procedures and inappropriate antimicrobial therapy and to identify common sources linked to transmission.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
A positive result suggests the presence of Shiga-like toxin 1 or 2. It is recommended that all positive specimens be cultured to confirm the presence of enteropathogenic coli.
A negative result does not rule out the presence of enteropathogenic Escherichia coli; detectable antigen levels may not be produced until 3-6 days after the development of symptoms.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Antibiotic treatment prior to specimen collection may affect this assay; some antibiotics have the potential to destroy the cell wall component detected in this enzyme-linked immunosorbent assay (ELISA).
This FDA-approved test was compared with Mayo's standard culture method for detecting Escherichia coli O157 using 46 reference specimens and 38 in-house specimens. The sensitivity (92%) and specificity (97%) of the assay was to equal culture. The assay had no cross reaction with stools containing other fecal pathogens including Aeromonas, Shigella sonnei, Beta strep (not Group A), Salmonella species (not typhi),Campylobacter jejuni , and yeast.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Karmali MA: Infection by verocytotoxin-producing Escherichia coli. Clin Microbiol Rev 1989;2:15-38
2. Karmali MA, Petric M, Lim C, et al: The association between idiopathic hemolytic uremic syndrome and infection by verotoxin-producing Escherichia coli. J Infect Dis 1985;151:775-782
3. Griffin PM, Ostroff SM, Tauxe RV, et al: Illnesses associated with Escherichia coli O157:H7 infections. A broad clinical spectrum. Ann Intern Med 1988;109:705-712
4. Wong CS, Jelacic S, Habeeb RL, et al: The risk of the hemolytic-uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections. N Engl J Med 2000;342:1930-1936