259. A Sensitive Multiplex, Real-Time PCR Assay for Detection of Shiga-Toxin Producing E. Coli from Stool Reveals Similar Incidence of Non-O157 and O157 Serotypes in Northern California
Session: Poster Abstract Session: Diagnostic Microbiology; Novel Molecular Methods
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
Background: Rapid and accurate detection of Shiga-toxin producing E. coli of all serotypes from patients with diarrhea is critical for medical management and for prevention of ongoing transmissions. 

Methods: We designed a multiplex, real-time PCR assay targeting the Shiga-toxin genes stx1 and stx2 and assessed the performance of the assay for detection of O157 and non-O157 Shiga-toxin producing E. coli from diarrheal stool samples enriched in GN broth.  To assess laboratory practices in our geographic area regarding the use of Shiga toxin testing, we also performed a telephone survey in Santa Clara County in which data were requested on current protocols for O157 E. coli and/or Stx testing. 

Results: We show that the multiplex, real-time PCR assay is 100% sensitive (95% confidence interval (CI) 89.1% to 100%) and 98.5% specific (95% CI 90.6% to 99.9%).  During a two-year post-validation period, the assay detected a greater number of positive samples from patients in Northern California compared to culture and PCR testing performed at a public health reference laboratory, with a positive predictive value of 95.6% (95% CI 87.6% to 99.1%).  Serotyping data showed an incidence rate of 51.2% for non-O157 STEC strains.  Additionally, a survey of 17 clinical laboratories in Northern California demonstrated that nearly 50% do not screen all stool specimens for the presence of Shiga toxins.

Conclusion: The findings from this study underscore the recommendations of the CDC for laboratories to test all diarrheal stool samples from patients with acute community-acquired diarrhea for non-O157 STEC in addition to O157 serotype using a sensitive assay.

Martina I. Lefterova, MD, PhD, Pathology, Stanford Hospital and Clinics, Stanford, CA, Kathleen A. Slater, Bsanta Clara County Public Health Laboratory, San Jose, CA, Indre Budvytiene, Stanford University, Palo Alto, CA, Patricia A. Dadone, Santa Clara County Public Health Laboratory, San Jose, CA and Niaz Banaei, MD, Departments of Pathology and Medicine, Division of Infectious Diseases and Geographic Medicine, Stanford University, Palo Alto, CA


M. I. Lefterova, None

K. A. Slater, None

I. Budvytiene, None

P. A. Dadone, None

N. Banaei, None

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