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Delaware Health & Social Services
Division of Public Health
Laboratory

LPAC - November 14, 2008

Shiga Toxin Producing Escherichia coli

Debbie Rutledge, Clinical Microbiology Lab Manager

Background

• In 1999- 100,000 illnesses, 3200 hospitalizations, 91 deaths in US;
• Asymptomatic shedding, non-bloody diarrhea, hemorrhagic colitis, HUS;
• contaminated food or H20 & infected animals or persons;
• O157 most recognized- others just as common;
• >100 serotypes, O157 sorbitol negative, Others undistinguishable. 

Conventional Culture

Testing for STEC

• Culture media
     – Sorbitol-MacConkey (SMAC) agar
     – Cefixime-Tellurite (CT)-SMAC
     – Chrom agar

• Disadvantages
     – Some E. coli O157:H7 can have unusual biochemical characteristics 
       (e.g., sorbitol positive)
     – Low numbers may not be isolated
     – Sensitivity of culturing for E. coli O157:H7 may be low (50-60%)
     – Misses non-O157:H7 STEC

STEC Non culture methods

• 1995, FDA cleared first rapid assay for detection of STEC from stools.
• EIA – Enzyme Immunoassay for detection of stx 1 & 2.
• Labs –rely on these tests rather than culture methods. 
• Lose epidemiologic and surveillance information without isolate. 

Non culture methods

• Pros:
     – Advantages for care of the individual patient.
     – Rapid and easy to perform.
     – Enables detection of non-O157 STEC isolates.

• Cons:
     – False positives – reportable disease.
     – Inability to easily obtain critical isolates needed for public health 
       surveillance activities.
• Antimicrobial resistance.
• PulseNet molecular subtyping.
• Detection of novel or altered strain types .

STEC in Delaware

Pathogen Detection and Characterization

DPHL STEC Recommendations 

• Clinical labs- submit shigatoxin positive broths and/or original stool;
• Tests original and new broths –stx 1 & 2  by EIA or PCR;
• Sub positive broths – tests up to 20 colonies for stx 1 & 2 by EIA or PCR;
• Look for O157 and screen colonies with RIM E.coli antisera;
• Confirm biochemically- ID of E.coli.

Serotyping & PFGE

• Serotype for O157 & top 6 “O” groups (026,045, 0103,0111,0121,0145);
• If unable to serotype –send to CDC;
• Pulse-Field Gel Electrophoresis- within 4 days from receipt- Pulsenet;
• Analyze gels and send to CDC Pulsenet database. 

Conclusions

• Timely laboratory diagnosis of STEC illness
     – prevent inappropriate treatment .
     – allow for supportive care to prevent HUS.
     – Requires communication between hospital and state PHLs to ensure 
       optimal testing.

• Including PCR testing to conventional testing algorithms - guide appropriate 
  and cost effective public health efforts and focuses resources on optimal 
  STEC recovery .

• The recover of STEC isolates is essential to the tracking of cases and 
  detection of outbreaks.

     – Enables prompt PFGE subtyping and further characterizations.
     – Allows for public health interventions (ie. Recalls) to prevent 
       additional infections.

Acknowledgements

• DPHL Clinical Microbiology Lab Staff
• Denise Toney, VA Division of Consolidated Laboratories
• 2008 APHL STEC Subcommittee
• Susan Shore, DPH Epidemiology