Prevalence of Enterohemorrhagic E. coli (EHEC)

Marler and Clark Retail Ground Beef Baseline Study: Phase 3

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.

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

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

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

Retail Ground Beef baseline StudyPhase III

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%

E. coli Serotypes in Retail Ground Beef Survey

31.6

11.610.5

9.5

6.35.3

4.23.2

2.11.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1

0

5

10

15

20

25

30

35

Inci

denc

e (%

)

6.22

2.00

0

1

2

3

4

5

6

7

Total IR (n=301) Total Confirmed (n=96)

Inci

den

ce (%

)Incidence of Non O157 EHEC in Retail Ground Beef Survey (n=5,070)

6.22

2.00

0.62

0

1

2

3

4

5

6

7

Total IR (n=301) Total Confirmed (n=96) O26, O45, O111, O121, O145, O103 (n=30)

Inc

ide

nc

e (%

)

Incidence of Non O157 EHEC in Retail Ground Beef Survey (n=5,070)

2.85

1.70

0

1

1

2

2

3

3

Total IR (n=138) Total Confirmed (n=86)

Inci

den

ce (%

)

Incidence of Salmonella in Retail Ground Beef Survey (n=5,070)

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.

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