Salmonella Enteritidis: Surveillance Data and Policy Implications

Alejandro Pérez, MPH

Enteric Diseases Epidemiology Branch

Division of Foodborne, Bacterial and Mycotic Diseases

National Center for Zoonotic, Vector-Borne, and Enteric Diseases

Centers for Disease Control and Prevention

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Glossary of Terms • Salmonella Enteritidis (SE) - the bacteria

Salmonella enterica serotype Enteritidis

• Serotype - strain of Salmonella based on reaction with specific antibodies

• Salmonellosis - the disease caused by infection by Salmonella enterica

• Isolate - Salmonella bacterium obtained from a single laboratory culture

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Salmonella • A genus of gram-negative, rod-shaped

bacteria

• Live in intestines and peri-reproductivetissues (ovaries, milk glands, etc)

• Few species, but thousands of serotypes

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Salmonellosis

• Disease caused by infection with Salmonella

• Symptoms include diarrhea, fever, abdominal cramps

• Starts 12-72 hours after infection and lasts 4-7 days

• Severe cases can result in hospitalization and can infect the blood and lead to death

• Infants, the elderly, and immunocompromised are most at risk

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Salmonella Enteritidis and eggs

• Eggs identified as primary vehicle for SE infection

• Exterior of eggs contaminated by contact with feces

• Interior of eggs contaminated via transovarian transmission

• In 1990’s it was estimated that 7% of egg farms had SE and 1 in 20,000 eggswere positive for SE

National Salmonella Surveillance

• Surveillance for individual patients • Salmonellosis is a nationally notifiable

disease

• Surveillance for foodborne outbreaks

• Two or more people ill due to a commonfood exposure

• May be reported to or recognized byhealth departments

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National Salmonella Surveillance System

• Established in 1970s • Collects information on individual patients

• Public Health Laboratory Information System • Electronic reporting of isolate data by public

health labs • Includes serotype information

• Passive surveillance

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0 5000

10000 15000 20000

25000 30000

70 73 76 79 82 85 88 91 94 97 00 03 06 Year

No.

Isol

ates

S. Typhimurium S. Enteriditis S. Newport S. Heidelberg

Top four Salmonella serotypes, 1970-2007

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0 2000 4000 6000 8000

10000 12000 14000

70 73 76 79 82 85 88 91 94 97 00 03 06 Year

No.

Isol

ates

S. Typhimurium S. Enteriditis S. Newport S. Heidelberg

Top four Salmonella serotypes, 1970-2007

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SE isolations, 1989-2007

0

2000 4000

6000

8000 10000

12000

89 91 93 95 97 99 01 03 05 07

Year

N o .

Is o l

a t e s

5,333

10,201

4,914

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SE rates by region,1970-2007

0

2

4

6

8

10

12

70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 06 Year

Inci

denc

e R

ate

(per

100

,000

)

New England Mid Atlantic Pacific Other Mountain

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Percent of Salmonella that is Salmonella Enteritidis - 1985

Less than 15% At least 15%, less than 25%CDC 25% or more

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Percent of Salmonella that is Salmonella Enteritidis - 1994

Less than 15%

25% or more At least 15%, less than 25%CDC

National Salmonella Surveillance System - Summary

• Salmonella Enteritidis currently mostreported Salmonella serotype

• Peaked in 1995, but still high with over 5,000 cases in 2007

• Spread quickly across the US starting in the northeastern states

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FoodNet

• Active surveillance for foodborne diseases in ten states

• Participate in conducting active surveillance, surveys, andepidemiologic studies

• Aim to gain better understanding of epidemiology of foodborne diseases

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FoodNet sites 1996-2007

15% of U.S. population 45.92007 45.42006 44.92005 44.52004 41.92003 38.02002 34.92001 30.62000 25.91999 20.71998 16.11997

14.31996

Pop (millions)

Year

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Relative rates of laboratory-diagnosed Salmonella Enteritidis cases, FoodNet sites, 1996 – 2008

0 0.2 0.4 0.6 0.8

1 1.2 1.4 1.6

96 -98

99 00 01 02 03 04 05 06 07 08

Year

Rel

ativ

e R

ate

The surveillance pyramid Reported

Culture-confirmed case

Lab tests for organism

Specimen obtained

Person seeks care Person becomes ill

Population exposed

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FoodNet’s contribution to the surveillance pyramid

Active surveillance

Population survey

Physician survey

Laboratory survey

Population exposed

Person becomes ill

Person seeks care

Specimen obtained

Lab tests for organism

Culture-confirmed case

Reported FoodNet:

FoodNet’s contribution to the surveillance pyramid

• Estimate that for every reported case of Salmonella Enteritidis, 37 cases go unreported

• Estimate that 16% of all Salmonella infections acquired outside the USA

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Estimate of SE infections, 2007

Reported 5,333 cases reported

Culture-confirmed case

Lab tests for organism

multiplied by 38 Specimen obtained

Person seeks care Person becomes ill

General population 202,654 estimated cases

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FoodNet - Summary • Relative rate of Salmonella Enteritidis

infection is on the rise

• There are 38 times more infections than what is reported through passive surveillance systems • Therefore over 200,000 SE cases in 2007

• 16% of infections are acquired abroad

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Foodborne Disease Outbreak Surveillance System

• State and local health departments investigate and report foodborne outbreaksto CDC

• Surveillance system started in 1973 and has been web-based since 1998

• Approximately 1,300 reports per year

• Data collected: number of cases, implicated food, pathogen, etc

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1096

1266

968

1328

1094

1320 1249

806

602645690

514 411

531533

140313391317

0

200

400

600

800

1000

1200

1400

1600

90 92 94 96 98 00 02 04 06 Year

No.

Out

brea

ks

Foodborne disease outbreak reports 1990- 2007

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0 10 20 30 40 50 60 70 80 90

90 92 94 96 98 00 02 04 06

Year

No.

Out

brea

ks

Outbreaks due to Salmonella Enteritidis, 1990 - 2007

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0 2 4 6 8

10 12 14 16

90 92 94 96 98 00 02 04 06

Year

% o

f All

Out

brea

ks

Percentage of outbreaks due to Salmonella Enteritidis, 1990 - 2007

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Determining egg association in SE outbreaks

• All outbreaks investigated by state/local health departments to determinecontaminated food vehicle

• All foods are considered regardless of etiology

• When traceback investigations are conclusive, SE of the same subtype isoften identified on the farms of origin

Attributing egg association to all cases

• Uncertainty in attributing proportion of

cases in egg-associated outbreaks to:

• Outbreaks with unknown food vehicle • Only ½ of outbreaks have vehicle identified

• Non-outbreak associated cases • Majority of SE cases are not associated with an

outbreak

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Egg-associated illnesses in SE outbreaks, 1985-2007

Egg status Vehicle of food Egg

Total determined known Associated Outbreaks 1,112 523 502 376 Illnesses 35,552 25,555 24,464 18,347

• High range estimate: 18,347 / 24,464 = 75%

• Low range estimate: 18,347 / 35,552 = 52%

• Mid range estimate: (75% + 52%) / 2 = 64%

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Foodborne Disease Outbreak Surveillance System - Summary

• Number of Salmonella Enteritidis outbreaks decreased early on but has leveled off

• 75% of SE outbreaks with known vehicle were due to eggs

• Mid-range estimate for all SE outbreaks due to eggs is 64%

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Estimated number of SE cases due

to eggs in the United States, 2007

• Reported SE cases: 5,333 • FoodNet multiplier: 38 • Proportion acquired outside US: 16% • Proportion due to eggs: 64%

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Estimated number of SE cases due to

eggs in the United States, 2007

• 5,333 x 38 = 202,654 total cases of SE

• 202,654 – (0.16 x 202,654) = 170,229 cases

of SE acquired in US

• 170,229 x 0.64 = 108,947 egg-associated cases

• Round to 109,000 egg-associated cases acquired in the USA in 2007

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Egg Quality Assurance Programs (EQAPs)

• Voluntary measures for minimizing contamination of eggs with Salmonella Enteritidis

• Follow Hazard Analysis Critical Control Point (HACCP) principles

• Designed around production, management, and monitoring practices

• Adopted in various states throughout 1990s

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Annualized change in incidence of SE in relation to adoption of EQAPs

-20

-10

0

10

20

30

40

-5 -4 -3 -2 -1 0 1 2 3 4 5

Year, relative to EQAP adoption

Ann

ualiz

ed c

hang

e in

SE

inci

denc

e re

lativ

e to

EQ

AP

adop

tion

(%)

States with five years of data (n=4) States with three years of data (n=6)

States with two years of data (n=7) States with one year of data (n=11)

Before EQAPs After EQAPs

0

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Conclusions • Salmonella Enteritidis estimated to cause

more than 200,000 illnesses a year

• Eggs estimated to cause approximately64% of these cases (ranging from 75%and 52%)

• Regulation of egg production has beenlinked with decreased SE incidence

• Control programs making progress, butneed to be standardized and more widelyadopted

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Acknowledgements

• National Surveillance Team • FoodNet and Outbreak Surveillance Team

• Dr Barbara Mahon • Dr Chris Braden