1. Shiga-toxigenic E. coli O157: Reservoirs and Transmission Routes
John R. Dunn, DVM, PhD
Tennessee Department of Health
Centers for Disease Control and Prevention

2. Shiga-toxigenic E. coli (STEC)
Intestinal bacterial flora
Gram negative rods
Somatic or O antigen (LPS)
Flagellar or H antigen
Serotype O:H
STEC virulence factor complement
Hemolysin
Intimin
Shiga toxin

3. Shiga toxin Distinguishing virulence factor Subunit toxin:
A: acts at ribosomal level, inhibits protein synthesis
B: binds glycolipid receptor in mammalian cells (renal endothelium)
Stx1, Stx2
Stx2 variants: 2c,2d,2e,2f

4. Human pathogens Symptoms: Diarrhea Hemorrhagic colitis
Hemolytic Uremic Syndrome (HUS)
Thrombotic thrombocytopenic purpura (TTP)

5. E. coli O157:H7

6. 1993
Large western states outbreak, 500 cases and 4 deaths
E. coli O157 Emergence
CDC-MMWR
Association of STEC with HUS, Karmali et al.
Karmali et al J.Infect.Dis.
Description of Shiga toxin: O’Brien, others
O’Brien and Holmes Microbiol.Rev.
O’Brien and LaVeck Infect.Immun.
1982
First clinical isolation, “Rare E. coli serotype”
Riley et al NEJM

7. Ruminant reservoir
Gansheroff and O’Brien (PNAS,2000): “…Higher prevalence rates than previously estimated”
Selective enrichment & Immunomagnetic separation (IMS)- Sensitive methods
Conventional culture techniques:
Swab samples
Direct plating +/- broth enrichment

8. Ruminant (Bovine) Reservoir
Asymptomatically colonized- transient but common intestinal flora
Seasonal- summer peak, winter nadir
Endemically unstable- by feedlot, pen, individual, farm, week
Periodic high isolation rates (epidemics)- feces, hide, oral cavity, environment, carcass

9. Two habitat model Primary habitat:
Excretion
Re-colonization
Environment
Death
Primary habitat:
large intestine, recto-anal junction?
warm, constant
nutrient rich
vigorous growth
Secondary habitat:
water, soil, sediment
cool, fluctuating
nutrient limiting
survival

10. E. coli O157:H7 Epidemiology
1. Trends- FoodNet data 2. Transmission routes

11. Foodborne Diseases Active Surveillance Network (FoodNet)
Established in 1996
Principle foodborne disease component of Emerging Infections Program (EIP)
DHHS (CDC, FDA), USDA (FSIS), and 10 participating state health departments

12. 2004 FoodNet Catchment Area
Catchment population 44.1 million persons
15.2% of U.S. population

13. 2004 Preliminary FoodNet Data
Pathogen
Total # isolates
Cases per 100,000
Salmonella
6,464
14.7
Campylobacter
5,665
12.9
Shigella
2,231
5.1
Cryptosporidium
613
1.3
E. coli O157
401
0.9
Yersinia
173
0.39
Vibrio
124
0.28
Listeria
120
0.27
Cyclospora 15
0.03

14. E. coli O157:H7
HP 2010
1.0 / 100,000

15. Incidence of E. coli O157 infections, by state, 1999-2002
Isolates / 100,000 pop/ year
3.0 – 6.2
1.7 – 2.9
0.9 – 1.6
0.2 – 0.8

16. 2
E. coli O157 1
Relative Rate
0.8
0.7
0.6
-42 (-54 to -28)
0.5
1999
2000
2001
2002
2003
2004
Year

17. Consistency in data sources: Decline in E. coli O157
FoodNet surveillance data- declines overall and in high incidence sites
FSIS data

18. Prevalence of E. coli O157:H7 in Ground Beef1
1 Results of raw ground beef products analyzed for E. coli O157:H7 in federal plants.
* In 1998 FSIS increased sample size from 25 g to 375g.
** In July 1999 FSIS changed to a more sensitive analytical method.

19. Foodborne transmission

20. Has HACCP led to a reduction in human incidence?
Excretion
Re-colonization
Environment
Death

21. Direct and indirect contact transmission

22. Direct contact transmission

23. Indirect contact (environmental) transmission

25. Recent fair outbreaks- E. coli O157
Fair Year # Ill
Medina county (OH)
Lorain county (OH)
Ozaukee county (WI)
Wyandot county (OH)
Lane county (OR)
Calaveras county (CA)
Fort Bend county (TX)
North Carolina State Fair
Florida (multiple fairs) >30

26. Summary STEC- diverse serotypes
Shiga toxin- distinguishing virulence factor
O157:H7 most common, best characterized
STEC O157:H7
Ruminant (cattle) reservoir
Survival for long periods in the environment

27. Summary (cont) STEC O157:H7 decline in FoodNet (HP 2010)
Consistent with FSIS data
Transmission from multiple sources
Foodborne
Direct and indirect animal contact (fairs and farms)

28. STEC public health challenges
Understand the epidemiology of Non-O157 STEC
Food safety
Ground beef / tenderized steaks- recent outbreaks of E. coli O157
Other vehicles- produce / waterborne outbreaks
Direct and indirect animal contact
Prevention- NASPHV compendium
Other measures- restrict children, treat animals, decontaminate environment

29. Questions?