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Shiga-toxigenic E. coli O157: Reservoirs and Transmission Routes

Shiga-toxigenic E. coli O157: Reservoirs and Transmission Routes. John R. Dunn, DVM, PhD Tennessee Department of Health Centers for Disease Control and Prevention. Shiga-toxigenic E. coli (STEC). Intestinal bacterial flora Gram negative rods Somatic or O antigen (LPS)

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Shiga-toxigenic E. coli O157: Reservoirs and Transmission Routes

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  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. 1993. Association of STEC with HUS, Karmali et al. Karmali et al. 1985. J.Infect.Dis. Description of Shiga toxin: O’Brien, others O’Brien and Holmes. 1987. Microbiol.Rev. O’Brien and LaVeck. 1983. Infect.Immun. 1982 First clinical isolation, “Rare E. coli serotype” Riley et al. 1983. 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. Excretion Re-colonization Environment Death Two habitat model • 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 data2. 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

  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. E. coli O157 -42 (-54 to -28) 2 1 Relative Rate 0.8 0.7 0.6 0.5 1996-1998 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. Excretion Re-colonization Environment Death Has HACCP led to a reduction in human incidence?

  21. Direct and indirect contact transmission

  22. Direct contact transmission

  23. Indirect contact (environmental) transmission

  24. Recent fair outbreaks- E. coli O157 FairYear# Ill • Medina county (OH) 2000 27 • Lorain county (OH) 2001 111 • Ozaukee county (WI) 2001 59 • Wyandot county (OH) 2001 88 • Lane county (OR) 2002 60 • Calaveras county (CA) 2002 4 • Fort Bend county (TX) 2003 25 • North Carolina State Fair 2004 108 • Florida (multiple fairs) 2005 >30

  25. 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

  26. 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)

  27. 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

  28. Questions?

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