1. Prevalence of Enterohemorrhagic E. coli (EHEC) Marler and Clark Retail Ground Beef Baseline Study: Phase 3

2. Introduction IEH has been commissioned by Marler and Clark to conduct a baseline study to determine the prevalence of non-O157 EHEC in ground beef. The project involves analysis of 5,070 ground beef samples purchased at retail markets throughout the country. IEH accepted the project with the condition that the names of the manufacturing establishments would not be released.

3. Enterohemorrhagic (EHEC): Pathogenic Shiga Toxin Producing E. coli (pSTEC) Several other serotypes of EHEC have been associated with HC, and HUS These serotypes are difficult to test for, mainly due to lack of convenient markers to allow for their detection Another impediment is lack of regulatory definition for the target organisms

4. Challenges in Defining EHEC/pSTEC Up to 20% of ground beef samples at retail can contain E. coli that produce Stx, great majority of these STEC strains lack the ability to cause illness in humans:  Stx is phage borne, generic E. coli can get infected with the phage  Stx alone is not sufficient to produce illness other factors such as eae, or subtilase are needed  All major serotypes of EHEC also contain EPEC members

5. The IEH Definition An E. coli strain is deemed to be EHEC/pSTEC if it:  Carries/produces at least one form of Stx  The strain should also be eae or Subtilase positive  All isolates will be serotyped to determine if they belong to one of the common serotypes in the USA (O26, O45, O111, O121, O145)  Other serotypes will also be considered to be EHEC/pSTEC if they possess the appropriate virulence factors

6. Retail Ground Beef baseline Study Phase III

7. Human isolates of non-O157 STEC, by serogroup, 1983-2002 Brooks, JID 2005;192:1422 N = 940 isolates % of isolates 55 O groups, each <1% 70%

12. Conclusion A total of 5070 retail ground beef samples were analyzed for the presence of non-O157 EHECs 301 samples were presumptive for the EHECs, 86 samples were confirmed, and 30 of the 86 belonged to the CDC-6 serotypes 138 of the 5070 samples were presumptive positive for Salmonella, 86 of the 138 were confirmed positives for Salmonella.

13. Conclusions Substantial number of positives have the Subtilase/Stx genotypes We have found some of the more pathogenic serotypes which are not included in the CDC-6 From a public health point of view the CDC-6 approach is flawed The results of the current study are based on N=1 sampling plan, as such, the data is an underestimation of the burden of the target organisms