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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

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

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?