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:
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•
•
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Diarrhea
Hemorrhagic colitis
Hemolytic Uremic Syndrome (HUS)
Thrombotic thrombocytopenic purpura (TTP)
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E. coli O157:H7
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1993
E. coli O157
Emergence
Large western
states outbreak, 500
cases and 4 deaths
CDCMMWR.
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.
1982
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First clinical isolation,
“Rare E. coli serotype”
O’Brien and LaVeck.
1983. Infect.Immun.
Riley et al.
1983. NEJM
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
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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
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Two habitat model
Primary habitat:
large intestine, rectoanal junction?
• warm, constant
• nutrient rich
• vigorous growth
Secondary habitat:
water, soil, sediment
• cool, fluctuating
• nutrient limiting
• survival
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Excretion
Re-colonization
Death
Environment
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 persons
15.2% of U.S. population
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2004 Preliminary FoodNet Data
Pathogen
Total #
isolates
Cases per
100,000
6,464
5,665
2,231
613
14.7
12.9
5.1
1.3
E. coli O157
Yersinia
Vibrio
401
173
124
0.9
0.39
0.28
Listeria
Cyclospora
120
15
0.27
0.03
Salmonella
Campylobacter
Shigella
Cryptosporidium
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Cases per 100,000 persons
E. coli O157 Incidence in FoodNet Sites, 2004
2.2
2
E. coli O157:H7
1.7
1.3
1
0.9
HP 2010
0.9 0.8 0.8 0.8
1.0 / 100,000
0.5 0.4
0.3
0
All MN OR NY
sites
CT
CO
Site
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CA
TN NM MD GA
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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2
Relative Rate
E. coli O157
1
0.8
0.7
0.6
0.5
1996-1998
-42 (-54 to -28)
1999
2000
2001
2002
Year
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2003
2004
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
Percent Positives
1
0.8
0.6
0.4
0.2
0
95
1 Results
96
97
98*
99**
00
Fiscal Year
01
02
03
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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04
Foodborne transmission
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Has HACCP led to a reduction
in human incidence?
Excretion
Re-colonization
Death
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Environment
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 O157
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•
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•
•
•
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Fair
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)
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Year
2000
2001
2001
2001
2002
2002
2003
2004
2005
# Ill
27
111
59
88
60
4
25
108
>30
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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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
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Questions?
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