JCM Accepts, published online ahead of print on 30 July 2014 J. Clin. Microbiol. doi:10.1128/JCM.01231-14 Copyright © 2014, American Society for Microbiology. All Rights Reserved.
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Shiga Toxin-Producing Escherichia coli: A Single Center, 11-Year Pediatric Experience
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Emily I. Schindler,a,b Patricia Sellenriek,c Gregory A. Storch,d Phillip I. Tarr,e,f and Carey-Ann
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D. Burnhamb#
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Barnes Jewish Hospital, St. Louis, MOa; Department of Pathology and Immunology, Washington
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University School of Medicine, St. Louis, MOb; St. Louis Children’s Hospital, St. Louis, MOc;
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Division of Infectious Diseases, Edward Mallinckrodt Department of Pediatrics, Washington
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University School of Medicine, St. Louis, MOd; Division of Gastroenterology, Edward
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Mallinckrodt Department of Pediatrics, Washington University School of Medicine, St. Louis,
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MOe; Department of Molecular Microbiology, Washington University School of Medicine, St.
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Louis, MOf
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Running Head: Detection of STEC in Children with HUS
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#
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Department of Pathology and Immunology
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660 S Euclid Ave, Campus Box 8118
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St. Louis, MO 63139
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[email protected].
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Telephone: 314-362-1547
Address correspondence to: Carey-Ann Burnham
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Abstract: The aim of this study was to identify best practice for the detection of Shiga toxin-
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producing Escherichia coli (STEC) in children with diarrheal illness treated at a tertiary care
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center: sorbitol-MacConkey (SMAC) agar culture, enzyme immunoassay (EIA) for Shiga toxin,
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or the use of both methodologies simultaneously. STEC were detected in 100 of 14,997 stool
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specimens submitted for enteric culture (0.7%), of which 65 were E. coli O157. Among E. coli
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O157, 57 (88%) were identified by both SMAC and EIA, 6 (9%) by SMAC alone, and 2 (3%) by
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EIA alone. Of the 62 individuals with diarrheal hemolytic uremic syndrome (HUS) seen at our
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institution during the study period, 16 (26%) had STEC isolated from culture at our institution
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and 15 (24%) had STEC isolated at other institutions. No STEC was recovered in 31 cases
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(50%). Of the HUS cases in which an STEC was isolated, 28 (90%) were attributable to E. coli
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O157 and 3 (10%) were attributable to non-O157 STEC. Consistent with previous studies, we
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have determined that a subset of E. coli O157 STEC will not be detected if an agar based method
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is excluded from the enteric culture workup; this has both clinical and public health implications.
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Best practice would be concomitant use of an agar based method and a Shiga toxin EIA, but a
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Shiga toxin EIA should not be considered to be an adequate stand-alone test for detection of E.
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coli O157 in clinical samples.
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Introduction:
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Shiga toxin-producing Escherichia coli (STEC) cause a spectrum of disease, with
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manifestations ranging from mild, self-limited diarrhea to the life-threatening hemolytic uremic
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syndrome (HUS) (1-7). The incidence and severity of STEC infection are highest in children,
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with a disproportionate number of HUS cases reported in this group (7-10). E. coli O157:H7 is
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the serotype most often implicated in HUS worldwide (1, 9, 11-15).
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In 2009, the US Centers for Disease Control and Prevention (CDC) published guidance
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indicating that laboratories should simultaneously include a selective and differential agar-based
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medium to detect E. coli O157 and a test to detect Shiga toxins or Shiga toxin genes on all stools
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submitted for bacterial culture (16). These complementary methods are recommended because
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of the increasing recognition that non-O157:H7 STEC cause disease, and lack of evidence that
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STEC EIA is as good as or better than SMAC agar screening for the detection of E. coli O157,
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which remains the most clinically actionable of the STEC serotypes. Furthermore, some studies
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suggest toxin EIA is inferior to SMAC agar screening for detecting E. coli O157:H7 (14, 17-24).
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Infections with STEC are rare (FoodNet data suggest that approximately 4,000 cases of
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E. coli O157:H7 infection occur annually in the United States) (25), but for those infected, there
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are considerable benefits to making a timely diagnosis. Specifically, the earlier a microbiologic
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diagnosis is attained, the better the clinical outcome (26). Moreover, by identifying STEC as the
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probable cause of an often quite severe illness, clinical care can be focused. However, concern
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remains that uniform screening of all stools for these pathogens has little public health or clinical
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value. Advocates for limiting STEC testing to “request-only” status encourage laboratories to
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consider local disease prevalence, seasonal incidence, and cost before implementing the CDC
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guidance (24, 27, 28). The counter-point to this argument is that broad STEC screening prevents
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severe clinical outcomes by early detection and optimization of care. Best practice dictates
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intravenous hydration and conservative management of severe diarrhea be instituted as
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expeditiously as possible, and the laboratory detection of an STEC often prompts this
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intervention (2, 26, 29).
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Considering the cost of parallel testing and the paucity of data on which to judge the
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merit of the CDC guidance, many laboratories do not seek STEC unless specifically requested,
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and nearly 10% of laboratories have abandoned agar-based testing in favor of exclusively
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performing EIA for Shiga toxin detection (30).
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The St. Louis Children’s Hospital (SLCH) Microbiology Laboratory has followed the
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practice of simultaneous SMAC culture and STEC EIA on all stool specimens since 2001; this
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practice was recommended by CDC in 2009. Our objective in this study was to report our
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microbiological and clinical experience with these pathogens between 2001 and 2011, and
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provide data to evaluate the relative value of each component of the recommended testing
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methodology.
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Methods:
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Population: All stool and rectal swab specimens submitted to the microbiology laboratory at
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SLCH for enteric bacterial culture from January 1, 2001 to December 31, 2011 were included in
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this analysis. Clinical and laboratory data pertaining to patients with positive SMAC and/or
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positive EIA results were extracted from electronic medical records. Cases of diarrhea-
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associated HUS were identified by reviewing all electronic medical records from the study
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period for patients with a primary or secondary diagnosis of HUS (ICD-9 code 283.11). HUS
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was defined stringently using the criteria of anemia (hematocrit