Prevalence of Enterohemorrhagic E. coli (EHEC) in Marler and Clark Retail Ground Beef

Baseline Study: Phase 3

Mansour Samadpour

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 5000 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 isolates55 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 (%

)

Incidence of Non O157 EHEC in Retail Ground Beef Survey (n=4,841)

6.22

1.96

0

1

2

3

4

5

6

7

Total IR (n=301) Total Confirmed (n=95)

Inci

denc

e (%

)

Incidence of Non O157 EHEC in Retail Ground Beef Survey (n=4,841)

6.22

1.96

0.62

0

1

2

3

4

5

6

7

Total IR (n=301) Total Confirmed (n=95) O26, O45, O111, O121, O145, O103 (n=30)

Inci

denc

e (%

)

Incidence of Salmonella in Retail Ground Beef Survey (n=4,841)

2.85

1.74

0

1

1

2

2

3

3

Total IR (n=138) Total Confirmed (n=84)

Inci

denc

e (%

)

Conclusions regarding Phase III

• 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

Effective use of the pSTEC group

• Process control• Process control• Process control• Our failure to control pathogens in

ground beef is due to: Lack of understanding the microbiological

aspects of the process Insufficient verification Lack of process control

Frequency of Positive Signals in Carcasses, Ground Beef, Trim, and Variety Meats

STEC

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EHEC

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O157

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Salmonella

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Variety Meats

H