Methods for Detection of STEC in Humans: An Overview

Timely and accurate diagnosis of Shiga toxigenic Escherichia coli (STEC) disease in humans is extremely important from both a public health and a clinical management perspective. In the outbreak setting, rapid diagnosis of cases and immediate notification of health authorities is essential for effective epidemiological intervention. Early diagnosis also creates a window of opportunity for therapeutic intervention. Agents capable of adsorbing and neutralizing free Shiga toxin (Stx) in the gut lumen have been described (1 ,2 ), and these are likely to be most effective when adminstered early in the course of disease, before serious systemic sequelae develop. Also, the clinical presentation of STEC disease can sometimes be confused with other bowel conditions; thus, early definitive diagnosis may prevent unnecessary invasive and expensive surgical and investigative procedures or administation of antibiotic therapy, which may be contraindicated (3 ). However, detection of STEC is fraught with difficulty, particularly for strains belonging to serogroups other than O157. In the early stages of infection, there may be very high numbers of STEC in feces (the STEC may constitute >90% of aerobic flora), but as disease progresses, the numbers may drop dramatically. In cases of hemolytic uraemic syndrome (HUS), the typical clinical signs may become apparent as much as 2 wk after the onset of gastrointestinal symptoms, by which time the numbers of the causative STEC may be very low indeed. Also, in some cases, diarrhea is no longer present and only a rectal swab may be available at the time of admission to the hospital, limiting the amount of specimen available for analysis. For these reasons, STEC detection methods need to be very sensitive and require minimal specimen volumes.