shiga-toxigenic e. coli o157:
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Shiga-toxigenic E. coli O157: Reservoirs and
Transmission Routes
John R. Dunn, DVM, PhD
Tennessee Department of Health
Centers for Disease Control and Prevention
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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
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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
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Human pathogens
Symptoms:
• Diarrhea• Hemorrhagic colitis• Hemolytic Uremic Syndrome (HUS)• Thrombotic thrombocytopenic purpura (TTP)
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E. coli O157:H7
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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.
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Ruminant reservoir
Gansheroff and O’Brien (PNAS,2000): “…Higher prevalence rates than previously estimated”
Conventional culture techniques:
•Swab samples
•Direct plating +/- broth enrichment
Selective enrichment & Immunomagnetic separation
(IMS)- Sensitive methods
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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
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Primary habitat:large intestine, recto-anal junction?• warm, constant• nutrient rich• vigorous growth
Secondary habitat: water, soil, sediment• cool, fluctuating• nutrient limiting• survival
Excretion
Re-colonization
Environment Death
Two habitat model
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E. coli O157:H7 Epidemiology
1. Trends- FoodNet data
2. Transmission routes
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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
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2004 FoodNet Catchment Area
Catchment population 44.1 million persons15.2% of U.S. population
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2004 Preliminary FoodNet DataPathogen Total #
isolatesCases 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
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E. coli O157:H7
E. coli O157 Incidence in FoodNet Sites, 2004
0.9
2.2
1.7
1.3
0.9 0.8 0.8 0.80.5 0.4 0.3
0
1
2
Allsites
MN OR NY CT CO CA TN NM MD GA
Site
Case
s per
100,
000 p
erso
ns HP 2010
1.0 / 100,000
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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
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1
0.8
0.7
0.6
0.5
2
1996-1998 1999 2000 2001 2002 2003 2004
Year
E. coli O157
Rel
ati
ve
Rat
e
-42 (-54 to -28)
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Consistency in data sources: Decline in E. coli O157
1. FoodNet surveillance data- declines overall and in high incidence sites
2. FSIS data
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Prevalence of E. coli O157:H7 in Ground Beef1
0
0.2
0.4
0.6
0.8
1
95 96 97 98* 99** 00 01 02 03 04Fiscal Year
Perc
ent P
ositiv
es
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.
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Foodborne transmission
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Excretion
Re-colonization
Environment Death
Has HACCP led to a reduction in human incidence?
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Direct and indirect contact transmission
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Direct contact transmission
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Indirect contact (environmental) transmission
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Recent fair outbreaks- E. coli O157Fair Year # 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
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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
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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)
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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
STEC public health challenges
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Questions?
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