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Epidemiology and Risk Assessment Morris Potter Center for Food Safety and Applied Nutrition Food and Drug Administration
Epidemiology and Risk Assessment
Morris Potter
Center for Food Safety and Applied Nutrition
Food and Drug Administration
Epidemiology and Risk Assessment
• Incidence of diseases that may be foodborne
• Proportion of these diseases that are foodborne
• Major food vehicles of transmission
• Characterization of conditions under which foodborne transmission occurs
Risk Assessment
• Hazard identification
• Exposure assessment
• Hazard characterization (dose-response)
• Risk characterization
Epidemiology
• Outbreak investigations
• Studies of sporadic foodborne disease
• Surveillance of human diseases
• Surveillance of pathogens in foods
Incidence of Potentially Foodborne Diseases
• Surveillance that is– Passive– Active
• Surveillance that is – Based on clinical diagnosis– Based on laboratory confirmation from human clinical
specimens
• Known population denominator permits calculation of rates of illness
Salmonella Enteritidis Incidenceby Region, United States, 1970-99
0
2
4
6
8
10
12
1970 72 74 76 78 80 82 84 86 88 90 92 94 96 98Year
Nu
mbe
r/10
0,00
0 po
p.
Total New England Mid Atlantic Pacific Other Mountain
CDC PHLIS data
Food-related Illness and Death in the United States
76 million illnesses323,000 hospitalizations 5,000 deaths
First comprehensive estimates by CDC
Based on passive nationwide surveillance, medical literature, early FoodNet statistics, and expert elicitation
Used for new cost estimates, risk-assessment, model for other disease estimates
Food-related Illness and Death in the United States
FoodNet: Foodborne Disease Active Surveillance Network
YEAR POPULATION (in millions)
1996 14.3
1997 16.1
1998 20.7
1999 25.9
2000 30.5
2001 34.3
2002 36.1
2003 37.4 13%
of U.S. population
Active Surveillance
• 7 bacterial pathogens: Campylobacter, E. coli O157, Listeria, Salmonella, Shigella, Vibrio, and Yersinia
• 2 parasitic organisms: Cryptosporidium and Cyclospora
• 3 syndromata: Hemolytic Uremic Syndrome (HUS), Guillain Barré Syndrome (GBS), congenital toxoplasmosis
• Foodborne disease outbreaks
Incidence of Infections with Pathogens under Surveillance, FoodNet 2002
1.7E. coli O157
1.4Cryptosporidium
0.44Yersinia
0.26Listeria
0.27Vibrio
0.11Cyclospora
10.3Shigella
13.4Campylobacter
16.1Salmonella
Cases per 100,000 personsPathogen
Relative Rates of Laboratory-Diagnosed Cases of Campylobacter, Listeria, & Yersinia,
By Year 1996 - 2002
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1996 1997 1998 1999 2000 2001 2002
Rel
ativ
e R
ate
Campylobacter Listeria Yersinia
Relative Rates of Laboratory-Diagnosed Cases of Salmonella, E. coli O157, & Shigella,
By Year, 1996 - 2002
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1996 1997 1998 1999 2000 2001 2002
Rel
ativ
e R
ate
Salmonella E. coli O157 Shigella
Rate/ 100,000
0
50
100
150
<1 1-4 5-12 13-19 20-29 30-39 40-49 50-64 65-74 75+
Age group
Campylobacter Salmonella
Incidence of Campylobacter and Salmonella Infections in FoodNet by Age Group
Percentage of Cases Hospitalized, FoodNet, by Pathogen
0
20
40
60
80
100Percent
Epidemiology and Risk Assessment
• Incidence of diseases that may be foodborne
• Proportion of these diseases that are foodborne
• Major food vehicles of transmission
• Characterization of conditions under which foodborne transmission occurs
Incidence of Foodborne Disease
• Expert elicitation –
Proportion foodborne
• Population-based sporadic case studies – Specific attribution
Foodborne Disease Outbreaks, Passive Nationwide System, United States, 2000
Etiology Number NumberOutbreaks Cases
Bacterial 226 6528Chemical 37 185Parasitic 6 169Viral 176 7208Multiple Etiologies 3 22
Total Confirmed Etiology 448 14112Total Unknown Etiology 969 11931
Total 2000 1417 26043
Outbreaks Reported to FoodNet and Nationwide Surveillance System, 1998-1999
FoodNetPassive
Rate/million population 10.3 4.5
Known etiology 30% 28%
Salmonella 11% 32%
Shigella 2% 4%
E. coli O157 1% 7%
Epidemiology and Risk Assessment
• Incidence of diseases that may be foodborne
• Proportion of these diseases that are foodborne
• Major food vehicles of transmission
• Characterization of conditions under which foodborne transmission occurs
Major Food Vehicles
• Sometimes the biology of the agent identifies the vehicle
• For other pathogens– Outbreak investigations– Sporadic case studies– Pathogen surveillance
in foods
Major Food Vehicles for Specific Foodborne Pathogens
Outbreak investigations
Sporadic case-control studies
Food microbiology-based surveillance
Sporadic Case Studies
• Sporadic cases generally more common
• May have different epidemiologic characteristics and control strategies
• Studied by same methods as outbreaks but more difficult without clustering of cases
• FoodNet primarily established as a vehicle to study sporadic foodborne disease
Case-Control Studies of Sporadic Foodborne Disease
• Hazard identification
• Attribution to food
• Association of specific food-pathogen combinations
• If population-based, studies provide rates that can be generalized
• Salmonella
• Campylobacter
• E. coli O157
• Cryptosporidium
• Listeria
• Infant illness: (Salmonella, Campylobacter)
• Salmonella Newport
• Salmonella Enteritidis
FoodNet Case Control Studies
Surveillance Outbreak Detection Algorithm (SODA)• PC-based program for detecting Salmonella and Shigella outbreaks
Electronic Foodborne Outbreak Reporting System (EFORS)• Web-based system for reporting foodborne disease outbreaks
DPDx• Parasitic diagnostic support for states by videoconference
PulseNet • National network of laboratories for molecular fingerprinting of foodborne
pathogens for rapid comparison of “fingerprints” with central database
• Enhances detection of common source outbreaks, especially geographically dispersed outbreaks
Calicinet• Enhanced viral diagnostics and subtyping
Improving Surveillance for Foodborne Disease
PulseNet USA• National network of laboratories for molecular
fingerprinting of foodborne pathogens– All 50 states, CDC, FDA, and FSIS– Plans to add additional USDA laboratories and
possibly academic and industry laboratories
• Standardized protocols allows rapid comparison of digital images of fingerprints with central data base
• Enhances detection of common-source outbreaks, especially multistate outbreaks
PulseNet Expansion
• Geographic Expansion • PulseNet Canada• PulseNet Europe• PulseNet Asia Pacific• PulseNet Latin America (2004)
• Microbial Expansion• Methodological Expansion
PulseNet Expansion
• Geographic Expansion • Microbial Expansion
• Current: E. coli O157, Salmonella, Listeria, Shigella, Campylobacter
• Future: Non-O157 STEC, Vibrio cholerae, Yersinia enterocolitica, V. parahaemolyticus, Clostridium perfringens
• Methodologic Expansion• Current: Rapid standardized PFGE protocols• Future: MLVA, MLST, Microarrays, other
Epidemiology and Risk Assessment
• Incidence of diseases that may be foodborne
• Proportion of these diseases that are foodborne
• Major food vehicles of transmission
• Characterization of conditions under which foodborne transmission occurs
Characterization of Conditions of Foodborne Transmission
• Frequency and level of contamination
• Dose-response relationship
• Important antecedent factors
Qualitative Food Microbiology Data
ProductProduct Total SamplesTotal Samples % Positive% Positive
Fresh soft cheeseFresh soft cheese 29312931 0.170.17
Bagged SaladsBagged Salads 29662966 0.740.74
Blue-veined CheesesBlue-veined Cheeses 16231623 1.421.42
Mold-Ripened CheesesMold-Ripened Cheeses 13471347 1.041.04
Seafood SaladsSeafood Salads 24462446 4.704.70
Smoked SeafoodSmoked Seafood 26442644 4.314.31
Luncheon MeatsLuncheon Meats 91999199 0.890.89
Deli SaladsDeli Salads 85498549 2.362.36
TOTALTOTAL 31,70531,705 1.821.82
NFPA/JIFSAN Retail Study
Quantitative Food Microbiology DataOf 9,199 deli meat samples, 82 (0.9%) were Lm positive• 42 samples 0.04 – 0.1 cfu/g• 20 samples >0.1 –1 cfu/g• 10 samples >1-10 cfu/g• 2 samples 10-100 cfu/g• 7 samples 100-1000 cfu/g• 1 sample 103 to 104 cfu/g77% of the RTE meat samples were pre-packaged by the
manufacturer -- 0.4% were Lm positive23% of the RTE meat samples were deli-packed -- 2.7%
were Lm positiveNFPA/JIFSAN Retail Study
Exposure AssessmentFrequency of food contamination at retail
Number of Lm in contaminated samples
Lm growth potential in foods
Amount consumed/serving
Number of Lm consumed per serving
Storage time and temperature in home
Log reduction in reheated franks
Exposure Assessment: Other Factors to Consider
• Home refrigerator temperatures
• Percent of frankfurters reheated
• Effect of temperature on growth rate
• Effect of temperature on extent of growth
Hazard Characterization: probabilityof illness and death as a function of
number of L. monocytogenes ingested • Dose-response curve from mouse studies• Area under the curve set by FoodNet data on
human listeriosis• Other factors:
– Variation in virulence of L. monocytogenes isolates– Variation in susceptibility within age groups– Variation in susceptibility between age groups– Variation in fatality to hospitalization ratio
Dose of Listeria and Mortality in Mice
6 0 1 3 4
40
80
90
5
50
30
2
20
10
100
Data
Exponential
7
70
0
60
Dose (Log10 cfu)
Human Listeriosis Cases to be Distributed
within the Mouse Dose-Response Curve Sub- FoodNet Reported National Projected
Population Listeriosis in 4 Years Annual Listeriosis
_________ Cases Deaths Cases Deaths
Neonatal 38 3 216 16
Elderly 194 52 1159 307
Other 113 10 701 67
Total 345 65 2078* 390
Neonatal cases were multiplied by 2.5 to account for under-ascertainment, giving a case total for all listeriosis of 2400 for purposes of analysis.
Current Foodborne Disease Epidemiology
• Documents that too much food-related illness and death occurs
• Poorly characterizes the diseases
• Complicates risk ranking and priority setting
• Biased toward traditional bacterial enteric pathogens and foods of animal origin
Enhanced Foodborne Disease Epidemiology
• Improved health outcome data– Better diagnostics and subtyping– Enhanced epidemiologic follow-up– More quantitative data
• Improved food chain information– Surveillance based on food microbiology– Linkage of in-line indicators with health outcomes
• Improved risk assessments
