FDA/NSTA Web Seminar:

Food Safety and Nutrition

LIVE INTERACTIVE LEARNING @ YOUR DESKTOP

Thursday, April 26, 2007

7:00 p.m. to 8:00 p.m. Eastern time

Foodborne Illness Outbreak InvestigationOutbreak Investigation Surveillance and Epidemiology Surveillance and Epidemiology

“Be the Detective”“Be the Detective”

Patrick McCarthy, PhD, MPH

Food & Drug AdministrationU.S. Dept of Health and Human Services

USDA Food Safety and Inspection Service

– Responsible for ensuring safety of meat, poultry, and some egg products

US Food & Drug Administration

• Responsible for ensuring safety of all other food products

Estimates of foodborne illness and death based on surveillance databased on surveillance data

• 325,000 hospitalizations each year• 5,000 deaths each year• 14 million illnesses due to known pathogens• 62 million illnesses due to unknown pathogens

Paul Mead-CDC-1999

Factors Pushing the Numbers Up

• Globalization of the food supply

• Perceived healthiness of raw fruits and vegetables

• Increase in susceptible population

• Eating out more

• International travel

D Swerdlow, S Altekruse 1998

Which agency regulates these products: Type a “U” for USDA, or an “F” for FDA

Vegetables Meat Spices Seafood

Chicken Diet supplements

Infant formula Pizza with a lot of meat

Why do we do surveillance?

• Identify emerging problems and stimulate actions to address them

• Take prompt control actions

• Identify and interpret trends in foodborne disease

• Determine the consequences of foodborne illness

• Evaluate intervention programs

• Set goals, priorities, policies, training, etc. for food safety

How is foodborne illness recognized?

• From patients or someone close to patients • Report from MD, RN, laboratory, etc.• Review of national surveillance data

– Salmonella Outbreak Detection Algorithm(SODA)

– PulseNet– FoodNet

• Rarely: local newspaper or television news report

Viruses67%

Protozoa3%

Bacteria30%

Percentage of Foodborne Illness Attributable to Known

Pathogens

Mead et al., 1999

Identify what you think is the best reason to have a foodborne illness

surveillance program?

1.

2.

3.

Foodborne Outbreaks - FDA products only

Year Produce Sprouts Dairy Eggs Proc. foods

Seafood Cosmetics Total

1996 2 2 0 34 4 26 0 68

1997 4 3 1 32 1 8 0 49

1998 6 3 0 25 1 6 0 41

1999 9 6 0 30 3 8 0 56

2000 5 1 1 28 5 6 0 46

2001 8 3 3 16 1 13 0 44

2002 6 2 4 21 1 3 0 37

2003 6 5 4 15 3 6 0 39

2004 10 2 6 2 5 9 1 35

2005 7 0 3 4 4 6 2 26

Total 63 27 22 207 28 91 3 441

Why investigate outbreaks?

• Identify and eliminate sources of exposure

• Develop strategies to prevent future outbreaks

• Describe new diseases

• Learn more about existing diseases

• Evaluate existing prevention strategies

Why does it take so long?

Reported to health department

Culture-confirmed case

Lab tests for organism

Specimen obtained

Person seeks care

Person becomes ill

Population exposures

Determining Burden of Disease

Did you ever have a foodborne illness?

Yes ()

No (X)

If you answered yes to the previous poll question, did you report the illness to

the health department?

Yes ()

No (X)

Multiplication Factors

For Salmonella and other pathogens that cause non-bloody diarrhea the degree of underreporting has been estimated at about 38 fold.

For EC0157H7 and Shigella which cause bloody diarrhea - underreporting has been estimated at about 20 fold.

P Mead – CDC 1999

Burden of Illness

Measuring the Association Between Exposure and Disease

Attach Rate Table – Cohort Study

FoodExposure

Ate Food - YesTotal Ill % Ill

Ate Food - NoTotal Ill % Ill

AssociationRR 95% CI

Oysters 19 12 63% 20 14 70% 0.9 0.58 -1.41

Salad 28 24 86% 11 2 18% 4.7 1.33 -16.8

Baked Ham

22 16 73% 17 10 59% 1.2 0.77 -1.98

Cohort study: relative risk

ill not ill

Exposed 24 4

Unexposed 2 9

• At start of cohort study you know everyone’s exposure status

• total exposed = 28; total unexposed = 11

• go forward in time and determine risk of getting ill

• risk if exposed = 24 / 28 = 0.857 • risk if not exposed = 2 / 11 = 0.182

• Relative Risk = 0.85 / 0.18 = 4.71

28

11

total

http://www-unix.oit.umass.edu/~exsc597j/Epi2000/ENGLISH/HELP/statist.htm

Take Home Message

• In cohort studies the relative risk (RR) compares rate of illness in the exposed group to rate of illness in the unexposed group.

• In case-control studies the odds ratio (OR) is the odds in favor of exposure among cases compared to the odds in favor of exposure among the controls.

• if RR or OR = 1, or the 95 % CI includes 1 then the result is not considered statistically significant

• If RR or OR is less than 1 may mean food item is "protective“

Review: What pathogen is associated with the most foodborne illness ?

Bacteria Protozoa Viruses

Traceback

• Track food items back to their source (product type, lot #, delivery time, etc.)

Traceback - protocol

• Traceback protocol includes– extensive record reviews – extensive interviews – records / information collected includes

shipments, inventories, transportation, etc.

– data analyses

Traceback - case study

Details:– AZ; 19-ill; church group, restaurant, July 5th

– NV; 12-ill; friends, restaurant, July 8th

– CA; 14-ill; party, restaurant supplied food, July 9th

• lab reports all cases have identical PFGE pattern• case-control study is conducted• spinach is implicated• traceback is initiated to determine source of the

spinach

Scenario - common farm

Restaurant BSan Diego, CA

Spinach Distributor ADenver, CO

Restaurant CLas Vegas, NV

Restaurant APhoenix, AZ

Farm ANogales, AZ

Farm BSalinas, CA

Farm CTucson, AZ

No common restaurant so

distributors can be eliminated as a

possible contamination source.

Spinach Distributor BSalinas, CA

Farm B supplies both distributors and is suspected contamination source.

Product Contamination

• 4 important sources

– soil

– water

– farm workers

– domestic and feral animals

Outbreak of Escherichia coli O157 Infections Outbreak of Escherichia coli O157 Infections Associated with Fresh Spinach Associated with Fresh Spinach

August-September 2006August-September 2006

• Early epi information– 3 possible processors in California– dozens of possible ranches

• Possible ongoing exposures so FDA advises consumers not to consume bagged spinach

• Actions taken by other countries based on

early information.

Question:Type your answers on the chat window

• Can you identify potential sources of produce contamination in addition to these:

–soil–water–farm workers–domestic and feral animals

E. Coli O157:H7 and Spinach

• Sept. 14th; FDA notified of multi-state investigation possibly linked to bagged spinach - possible ongoing exposures - early epi could not identify a firm or lot code

• Sept. 14th; California Food Emergency Response Team dispatched to three firms

• Sept. 14th; phone calls between CDHS, FDA, and implicated firms begin

• Sept. 15th; firm X initiated a voluntary recall

0

5

10

15

20

25

30

1 4 7 10 13 16 19 22 25 28 31 3 6 9 12 15 18 21 24

Num

ber of co

nfirm

ed c

ase

s

August

September

Date of initial symptom onset

Number Of Cases by Date of Illness Onset

United States, August-September, 2006

August 15, 2006

Lot -227 production date

All data is preliminary

Baby Spinach Harvesting

• Results:

– E.coli O157:H7 found on 4 ranches

– 9 isolates, from 1 ranch were PFGE indistinguishable from outbreak strain (1 stream, 1 pig feces, 7 cow feces)

• ranch is primarily a beef cattle operation

• a stream on the property - ideal habitat for wildlife – feral pigs, etc.

• well is shallow and sits in a slight depression in the field.

Produce Outbreaks some lessons learned

• Leafy vegetables have elevated levels of Leafy vegetables have elevated levels of bacteria due to large surface areabacteria due to large surface area

• Bacteria tends to adhere and accumulate in Bacteria tends to adhere and accumulate in structures and at cut surfaces - once structures and at cut surfaces - once internalized, pathogens are difficult to removeinternalized, pathogens are difficult to remove

• Pathogen survival varies greatly

• Negative lab result ≠ absence of pathogen

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