Shiga toxin-producing Escherichia coli, Idaho

Long-Term Sentinel Surveillance for Enterotoxigenic Escherichia coli and Non-O157 Shiga Toxin-Producing E. coli in Minnesota

Sentinel surveillance in Minnesota revealed that enterotoxigenic E. coli (ETEC) and non-O157 Shiga toxin-producing E. coli are common enteric pathogens; ETEC was the second leading bacterial pathogen in an urban site; 39% of ETEC were domestically acquired.

Background. Enterotoxigenic Escherichia coli (ETEC) and non-O157 Shiga toxin-producing E. coli (STEC) are not detected by conventional culture methods. The prevalence of ETEC infections in the United States is unknown, and recognized cases are primarily associated with foreign travel. Gaps remain in our understanding of STEC epidemiology.

Methods. Two sentinel surveillance sites were enrolled: an urban health maintenance organization laboratory (Laboratory A) and a rural hospital laboratory (Laboratory B). Residual sorbitol MacConkey (SMAC) plates from stool cultures performed at Laboratory A (1996–2006) and Laboratory B (2000–2008) were collected. Colony sweeps from SMAC plates were tested for genes encoding STEC toxins stx1 and stx2 (1996–2008) and ETEC heat-labile and heat-stable toxins eltB, estA 1, 2 and 3 (2000–2008) by polymerase chain reaction (PCR)-based assays.

Results. In Laboratory A, a bacterial pathogen was identified in 7.0% of 21 970 specimens. During 1996–2006, Campylobacter was the most common bacterial pathogen (2.7% of cultures), followed by Salmonella (1.2%), Shigella (1.0%), and STEC (0.9%). Among STEC (n = 196), O157 was the most common serogroup (31%). During 2000–2006, ETEC (1.9%) was the second most common bacterial pathogen after Campylobacter (2.6%). In Laboratory B, of 19 293 specimens tested, a bacterial pathogen was identified for 5.5%, including Campylobacter (2.1%), STEC (1.3%), Salmonella (1.0%), and ETEC (0.8%). Among STEC (n = 253), O157 was the leading serogroup (35%). Among ETEC cases, 61% traveled internationally.

Conclusions. Enterotoxigenic E. coli and STEC infections were as common as most other enteric bacterial pathogens, and ETEC may be detected more frequently by culture-independent multiplex PCR diagnostic methods. A high proportion of ETEC cases were domestically acquired.

Shiga toxin-producing Escherichia coli: a single-center, 11-year pediatric experience

The aim of this study was to identify the best practices for the detection of Shiga toxin-producing Escherichia coli (STEC) in children with diarrheal illness treated at a tertiary care center, i.e., sorbitol-MacConkey (SMAC) agar culture, enzyme immunoassay (EIA) for Shiga toxin, or the simultaneous use of both methods. STEC was detected in 100 of 14,997 stool specimens submitted for enteric culture (0.7%), with 65 cases of E. coli O157. Among E. coli O157 isolates, 57 (88%) were identified by both SMAC agar culture and EIA, 6 (9%) by SMAC agar culture alone, and 2 (3%) by EIA alone. Of the 62 individuals with diarrheal hemolytic uremic syndrome (HUS) seen at our institution during the study period, 16 (26%) had STEC isolated from cultures at our institution and 15 (24%) had STEC isolated at other institutions. No STEC was recovered in 31 cases (50%). Of the HUS cases in which STEC was isolated, 28 (90%) were attributable to E. coli O157 and 3 (10%) were attributable to non-O157 STEC. Consistent with previous studies, we have determined that a subset of E. coli O157 infections will not be detected if an agar-based method is excluded from the enteric culture workup; this has both clinical and public health implications. The best practice would be concomitant use of an agar-based method and a Shiga toxin EIA, but a Shiga toxin EIA should not be considered to be an adequate stand-alone test for detection of E. coli O157 in clinical samples.

Shiga toxin-producing Escherichia coli O157 is more likely to lead to hospitalization and death than non-O157 serogroups--except O104

The clinical spectrum following infection with Shiga toxin-producing Escherichia coli (STEC) is wide ranging and includes hemorrhagic colitis and life-threatening hemolytic uremic syndrome (HUS). Severity of STEC illness depends on patients' age and strongly on the infecting strains' virulence. Serogroup O157 is often assumed to be more virulent than others. Age-adjusted population-based data supporting this view are lacking thus far.

We conducted a large retrospective cohort study among patients of community-acquired gastroenteritis or HUS diagnosed with STEC infection, reported in Germany January 2004 through December 2011. Age-adjusted risks for reported hospitalization and death, as proxies for disease severity, were estimated for STEC serogroups separately, and compared with STEC O157 (reference group) using Poisson regression models with robust error estimation.

A total of 8,400 case-patients were included in the analysis; for 2,454 (29%) and 30 (0.4%) hospitalization and death was reported, respectively. Highest risks for hospitalization, adjusted for age and region of residence, were estimated for STEC O104 (68%; risk ratio [RR], 1.33; 95% confidence interval [CI], 1.19–1.45), followed by STEC O157 (46%). Hospitalization risks for the most prevalent non-O157 serogroups (O26, O103, O91, O145, O128, O111) were consistently and markedly lower than for O157, with the highest RR for O145 (0.54; 95% CI, 0.41–0.70) and the lowest for O103 (0.27; 95% CI, 0.20–0.35). Mortality risk of O104 was similar to O157 (1.2% each), but the group of all other non-O157 STEC had only 1/10 the risk (RR, 0.09; 95% CI, 0.02–0.32) compared to O157.

The study provides population-based and age-adjusted evidence for the exceptional high virulence of STEC O157 in relation to non-O157 STEC other than O104. Timely diagnosis and surveillance of STEC infections should prioritize HUS-associated E. coli, of which STEC O157 is the most important serogroup.

Evaluation of a new chromogenic agar medium for detection of Shiga toxin-producing Escherichia coli (STEC) and relative prevalences of O157 and non-O157 STEC in Manitoba, Canada

This study assesses the detection performance of CHROMagar STEC medium relative to a reference cytotoxin assay and describes the current relative prevalence of O157 and non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes within the province of Manitoba, Canada. Over a 10-month period, 205 nonfrozen routine stool submissions to Cadham Provincial Laboratory (CPL) were used to assess the performance of CHROMagar STEC. Of the 205 stools, 14 were identified as true positives by a cytotoxin assay, with resultant CHROMagar STEC sensitivity, specificity, and positive predictive and negative predictive values of 85.7%, 95.8%, 60.0%, and 98.9%, respectively. Using a separate panel of 111 STEC strains, CHROMagar STEC was shown to support the growth of 96 (86.5%) isolates. To assess relative prevalence, attempts were made to isolate by any means all STEC strains identified at CPL over a 17-month period. Of 49 isolates (representing 86.0% of all STEC infections detected), only 28.6% were O157 STEC strains. Of the 35 non-O157 STEC strains, 29 were subjected to further molecular analysis. In contrast to earlier results from our area, carriage of stx(2) appears to have increased. Overall, although CHROMagar STEC is not recommended as a primary screen, our results indicate that it is an effective supplemental medium for the isolation of probable STEC strains. Increased isolation of these serotypes is warranted to better understand their prevalence, clinical characteristics, and epidemiology and aid in the development or enhancement of food safety control programs targeting all STEC serotypes.

Shiga toxin-producing Escherichia coli in children: diagnosis and clinical manifestations of O157:H7 and non-O157:H7 infection

Shiga toxin-producing Escherichia coli (STEC), a cause of food-borne colitis and hemolytic-uremic syndrome in children, can be serotype O157:H7 (O157) or other serotypes (non-O157). E. coli O157 can be detected by culture with sorbitol-MacConkey agar (SMAC), but non-O157 STEC cannot be detected with this medium. Both O157 and non-O157 STEC can be detected by immunoassay for Shiga toxins 1 and 2. The objectives of this study were first to compare the diagnostic utility of SMAC to that of the Premier EHEC enzyme immunoassay (Meridian Diagnostics) for detection of STEC in children and second to compare the clinical and laboratory characteristics of children with serotype O157:H7 STEC and non-O157:H7 STEC infections. Stool samples submitted for testing for STEC between April 2004 and September 2009 were tested by both SMAC culture and the Premier EHEC assay at Children's Hospital Boston. Samples positive by either test were sent for confirmatory testing and serotyping at the Hinton State Laboratory Institute (HSLI). Chart review was performed on children with confirmed STEC infection. Of 5,110 children tested for STEC, 50 (0.9%) had STEC infection confirmed by culture; 33 were O157:H7 and 17 were non-O157:H7. The Premier EHEC assay and SMAC culture detected 96.0% and 58.0% of culture-confirmed STEC isolates (any serotype), respectively, and 93.9% and 87.9% of STEC O157:H7 isolates, respectively. There were no significant differences in disease severity or laboratory manifestations of STEC infection between children with O157:H7 and those with non-O157 STEC. The Premier EHEC assay was significantly more sensitive than SMAC culture for diagnosis of STEC, and O157:H7 and non-O157:H7 STEC caused infections of similar severity in children.

Shiga-toxigenic Escherichia coli detection in stool samples screened for viral gastroenteritis in Alberta, Canada

Shiga-toxigenic Escherichia coli (STEC) is an important cause of diarrheal disease. The most notorious STEC serotype is O157:H7, which is associated with hemorrhagic colitis and hemolytic-uremic syndrome (HUS). As a result, this serotype is routinely screened for in clinical microbiology laboratories. With the bias toward the identification of the O157 serogroup in routine diagnostic processes, non-O157 STEC has been largely underrepresented in the epidemiology of STEC infections. This diagnostic bias is further complicated by the fact that many non-O157 STEC infections cause nonspecific gastroenteritis symptoms reminiscent of enteric viral infections. In this study, real-time PCR was used to amplify Shiga toxin genetic determinants (stx(1) and stx(2)) from enriched stool samples that were initially submitted for the testing of enteric viruses in patients with suspected viral gastroenteritis between May and September of 2006, 2007, and 2008 (n = 2,702). Samples were submitted from the province of Alberta, Yukon, the Northwest Territories, and Nunavut, Canada. A total of 38 samples (1.4%) tested positive for Shiga toxin genes, and 15 isolates were cultured for further characterization. Several of the serotypes identified (O157:H7, O26:HNM, O26:H11, O103:H25, O121:H19, and O145:HNM) have been previously associated with outbreaks and HUS. This study outlines the importance of combining molecular methods with classical culture techniques to enhance the detection of emerging non-O157 as well as O157 serotypes in diarrheal stool samples. Furthermore, atypical diarrhea disease caused by non-O157 STEC can be routinely missed due to screening only for viral agents.

Comparison of Shiga toxin-producing Escherichia coli detection methods using clinical stool samples

Molecular diagnostic tools capable of identifying Shiga toxin-specific genetic determinants in stool specimens permit an unbiased approach to detect Shiga toxin-producing Escherichia coli (STEC) in clinical samples and can indicate when culture-based isolation methods are required. It is increasingly recognized that clinically relevant STEC are not limited to the singular O157 serotypes, and therefore diagnostic assays targeting toxin-encoding determinants must be able to account for any genetic variation that exists between serotypes. In this study conventional PCR and four real-time PCR assays (HybProbe, TaqMan, SYBR Green, and LUX) targeting the stx1 and stx2 Shiga toxin coding sequences were used to identify STEC in enriched stool samples (n = 36) and a panel of O157 and non-O157 strains (n = 64). PCR assays targeting stx1 and stx2 had variable specificity and sensitivity values with enriched stool samples. Molecular assays using DNA from pure cultures revealed that some primers were not sensitive to all stx2 variants. This evaluation concluded that the TaqMan-based probes were most appropriate in high throughput clinical diagnostic laboratories in consideration of cost, turn around time, and assay performance.

Shiga toxins, and the genes encoding them, in fecal samples from native Idaho ungulates

Cattle are a known reservoir of Shiga toxin-producing Escherichia coli. The prevalence and stability of Shiga toxin and/or Shiga toxin genes among native wild ungulates in Idaho were investigated. The frequency of both Shiga genes and toxin was similar to that reported for Idaho cattle ( approximately 19%).

Phenotypic and genotypic characterization of verotoxin-producing Escherichia coli O103:H2 isolates from cattle and humans

Characterization of important non-O157 verotoxin-producing Escherichia coli (VTEC) has lagged considerably behind that of O157:H7 strains. This study characterized 91 VTEC O103:H2 strains from bovine and human sources and of North American and European origins by virulence or putative virulence genes, pulsed-field gel electrophoresis (PFGE) patterns, plasmid profiles, antimicrobial resistance, and colicin production. All strains were positive for vt1 and eae-epsilon; 97% were positive for ehxA; and all were negative for hlyA. Two strains carried vt2. There were 66 PFGE patterns grouped in six clusters, and there were 25 different plasmid profiles. Plasmid-encoded katP and etp genes were significantly more frequent in European than in North American human strains. The distribution of selected phenotypes was as follows: enterohemorrhagic E. coli (EHEC) hemolysin, 95%; colicin production, 38%; antimicrobial resistance, 58%. All the strains were negative for the alpha-hemolytic phenotype. In conclusion, the VTEC O103:H2 strains were diverse, as shown by PFGE, plasmid profiles, virulence markers, and antimicrobial resistance patterns, and all strains showed an EHEC hemolytic phenotype instead of the alpha-hemolytic phenotype that has been shown previously.