Shiga-toxigenic E. coli O157:

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Shiga-toxigenic E. coli O157:

  1. 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. 2. Shiga-toxigenic E. coli (STEC) <ul><li>Intestinal bacterial flora </li></ul><ul><ul><li>Gram negative rods </li></ul></ul><ul><ul><li>Somatic or O antigen (LPS) </li></ul></ul><ul><ul><li>Flagellar or H antigen </li></ul></ul><ul><ul><li>Serotype O:H </li></ul></ul><ul><li>STEC virulence factor complement </li></ul><ul><ul><li>Hemolysin </li></ul></ul><ul><ul><li>Intimin </li></ul></ul><ul><ul><li>Shiga toxin </li></ul></ul>
  3. 3. Shiga toxin <ul><li>Distinguishing virulence factor </li></ul><ul><li>Subunit toxin: </li></ul><ul><ul><li>A: acts at ribosomal level, inhibits protein synthesis </li></ul></ul><ul><ul><li>B: binds glycolipid receptor in mammalian cells (renal endothelium) </li></ul></ul><ul><li>Stx1, Stx2 </li></ul><ul><ul><li>Stx2 variants: 2c,2d,2e,2f </li></ul></ul>
  4. 4. Human pathogens <ul><li>Symptoms: </li></ul><ul><li>Diarrhea </li></ul><ul><li>Hemorrhagic colitis </li></ul><ul><li>Hemolytic Uremic Syndrome (HUS) </li></ul><ul><li>Thrombotic thrombocytopenic purpura (TTP) </li></ul>
  5. 5. E. coli O157:H7
  6. 6. E. coli O157 Emergence First clinical isolation, “Rare E. coli serotype” Description of Shiga toxin: O’Brien, others Association of STEC with HUS, Karmali et al. Large western states outbreak, 500 cases and 4 deaths 1982 1993 Karmali et al. 1985. J.Infect.Dis . O’Brien and Holmes . 1987. Microbiol.Rev. O’Brien and LaVeck . 1983. Infect.Immun. Riley et al. 1983. NEJM CDC- MMWR . 1993.
  7. 7. Ruminant reservoir <ul><li>Gansheroff and O’Brien ( PNAS ,2000): “…Higher prevalence rates than previously estimated” </li></ul><ul><li>Conventional culture techniques: </li></ul><ul><li>Swab samples </li></ul><ul><li>Direct plating +/- broth enrichment </li></ul>Selective enrichment & Immunomagnetic separation (IMS)- Sensitive methods
  8. 8. 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 Ruminant (Bovine) Reservoir
  9. 9. <ul><li>Primary habitat: </li></ul><ul><li>large intestine, recto-anal junction? </li></ul><ul><li>warm, constant </li></ul><ul><li>nutrient rich </li></ul><ul><li>vigorous growth </li></ul><ul><li>Secondary habitat: </li></ul><ul><li>water, soil, sediment </li></ul><ul><li>cool, fluctuating </li></ul><ul><li>nutrient limiting </li></ul><ul><li>survival </li></ul>Two habitat model Excretion Re-colonization Environment Death
  10. 10. E. coli O157:H7 Epidemiology 1. Trends- FoodNet data 2. Transmission routes
  11. 11. Foodborne Diseases Active Surveillance Network (FoodNet) <ul><li>Established in 1996 </li></ul><ul><li>Principle foodborne disease component of Emerging Infections Program (EIP) </li></ul><ul><li>DHHS (CDC, FDA), USDA (FSIS), and 10 participating state health departments </li></ul>
  12. 12. 2004 FoodNet Catchment Area Catchment population 44.1 million persons 15.2% of U.S. population
  13. 13. 2004 Preliminary FoodNet Data 0.9 401 E. coli O157 0.03 15 Cyclospora 0.27 120 Listeria 0.28 124 Vibrio 0.39 173 Yersinia 1.3 613 Cryptosporidium 5.1 2,231 Shigella 12.9 5,665 Campylobacter 14.7 6,464 Salmonella Cases per 100,000 Total # isolates Pathogen
  14. 14. E. coli O157:H7 HP 2010 1.0 / 100,000
  15. 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. 16. 1 0.8 0.7 0.6 0.5 2 1996-1998 1999 2000 2001 2002 2003 2004 Year Relative Rate E. coli O157 -42 (-54 to -28)
  17. 17. Consistency in data sources: Decline in E. coli O157 <ul><li>FoodNet surveillance data- declines overall and in high incidence sites </li></ul><ul><li>FSIS data </li></ul>
  18. 18. Prevalence of E. coli O157:H7 in Ground Beef 1 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. 19. Foodborne transmission
  20. 20. Has HACCP led to a reduction in human incidence? Excretion Re-colonization Environment Death
  21. 21. Direct and indirect contact transmission
  22. 22. Direct contact transmission
  23. 23. Indirect contact (environmental) transmission
  24. 25. Recent fair outbreaks- E. coli O157 <ul><li>Fair Year # Ill </li></ul><ul><li>Medina county (OH) 2000 27 </li></ul><ul><li>Lorain county (OH) 2001 111 </li></ul><ul><li>Ozaukee county (WI) 2001 59 </li></ul><ul><li>Wyandot county (OH) 2001 88 </li></ul><ul><li>Lane county (OR) 2002 60 </li></ul><ul><li>Calaveras county (CA) 2002 4 </li></ul><ul><li>Fort Bend county (TX) 2003 25 </li></ul><ul><li>North Carolina State Fair 2004 108 </li></ul><ul><li>Florida (multiple fairs) 2005 >30 </li></ul>
  25. 26. Summary <ul><li>STEC- diverse serotypes </li></ul><ul><ul><li>Shiga toxin- distinguishing virulence factor </li></ul></ul><ul><ul><li>O157:H7 most common, best characterized </li></ul></ul><ul><li>STEC O157:H7 </li></ul><ul><ul><li>Ruminant (cattle) reservoir </li></ul></ul><ul><ul><li>Survival for long periods in the environment </li></ul></ul>
  26. 27. Summary (cont) <ul><li>STEC O157:H7 decline in FoodNet (HP 2010) </li></ul><ul><ul><li>Consistent with FSIS data </li></ul></ul><ul><li>Transmission from multiple sources </li></ul><ul><ul><li>Foodborne </li></ul></ul><ul><ul><li>Direct and indirect animal contact (fairs and farms) </li></ul></ul>
  27. 28. <ul><li>Understand the epidemiology of Non-O157 STEC </li></ul><ul><li>Food safety </li></ul><ul><ul><li>Ground beef / tenderized steaks- recent outbreaks of E. coli O157 </li></ul></ul><ul><ul><li>Other vehicles- produce / waterborne outbreaks </li></ul></ul><ul><li>Direct and indirect animal contact </li></ul><ul><ul><li>Prevention- NASPHV compendium </li></ul></ul><ul><ul><li>Other measures- restrict children, treat animals, decontaminate environment </li></ul></ul>STEC public health challenges
  28. 29. Questions?

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