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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