Abstract
Shiga toxin-producing Escherichia coli (STEC) are important enteric pathogens responsible for sporadic cases and outbreaks of gastroenteritis. E.coli O157:H7/NM (STEC O157) are the most commonly known STEC serotypes but it is now increasingly apparent that non-O157 STEC serotypes have been underreported in the past because they were not part of routine screening in many front-line laboratories. The Canadian Public Health Laboratory Network (CPHLN) has identified the need for improved detection and surveillance of non-O157 STEC and has developed the following recommendations to assist in the decision-making process for clinical and reference microbiology laboratories. These recommendations should be followed to the best of a laboratory's abilities based on the availability of technology and resources. The CPHLN recommends that when screening for the agents of bacterial gastroenteritis from a stool sample, front-line laboratories use either a chromogenic agar culture or a culture-independent diagnostic test (CIDT). CIDT options include nucleic acid amplification tests (NAATs) to detect Shiga toxin genes or enzyme immunoassays (EIAs) to detect Shiga toxins. If either CIDT method is positive for possible STEC, laboratories must have a mechanism to culture and isolate STEC in order to support both provincial and national surveillance as well as outbreak investigations and response. These CPHLN recommendations should result in improved detection of STEC in patients presenting with diarrhea, especially when due to the non-O157 serotypes. These measures should enhance the overall quality of healthcare and food safety, and provide better protection of the public via improved surveillance and outbreak detection and response.
Highlights
Escherichia coli are part of the normal flora of the gut
If either culture-independent diagnostic test (CIDT) method is positive for possible Shiga toxin-producing Escherichia coli (STEC), laboratories must have a mechanism to culture and isolate STEC in order to support both provincial and national surveillance as well as outbreak investigations and response. These Canadian Public Health Laboratory Network (CPHLN) recommendations should result in improved detection of STEC in patients presenting with diarrhea, especially when due to the non-O157 serotypes
E. coli O157:H7/NM (STEC O157) are the most common STEC serotypes causing infection in humans, but many non-O157 STEC serotypes have been associated with serious illness and major outbreaks [2]
Summary
Escherichia coli are part of the normal flora of the gut. Shiga toxin-producing Escherichia coli (STEC) are intestinal pathogens. Improvements to laboratories’ ability to identify non-O157 STEC are based on the use of chromogenic and/or selective agars and culture-independent diagnostic tests (CIDT). Less common CIDTs include Shiga toxin detection by cell culture cytotoxicity assays or reverse passive latex agglutination test, and isolation of selected serogroups by O-antigen immunomagnetic bead-capture methods. These methods are not practical in most front-line microbiology laboratories. The Canadian Public Health Laboratory Network (CPHLN) recommends that when screening for the agents of bacterial gastroenteritis, front-line laboratories use one or more of three options for the detection of STEC: NAAT, culture on selective agar, or broth enrichment plus an EIA (Figure 1). It is imperative that front-line laboratories communicate with their referral public health laboratories to determine the required work-up for culture, isolation or characterization of isolates before submitting any samples
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