Post on 06-Jan-2018
description
Scientific Perspective on Listeria monocytogenes in
Ready-to-Eat Food
Régis Pouillot, DVM, PhDFDA / CFSAN / OAO /
Division of Risk and Decision Analysis /Risk Analysis Branch
Food Advisory Committee, Dec 7-8, 2015
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Outline
• Epidemiology
• Listeria monocytogenes in RTE food (and elsewhere)
• Listeria dose-response models
• New Data
3
EPIDEMIOLOGY
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Few cases, severe
Scallan et al., Emerg Infect Dis 17(1): 7-12.
Pathogen Estimated annual number of illnesses in the U.S.(domestically acquired, foodborne)
Estimated annual number of associated deaths
Listeria monocytogenes 1,600 255 (16% of cases)
Salmonella, non typhoidal 1.0 million 378 (.03% of cases)
Norovirus 5.5 million 149 (.002% of cases)
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Most cases are sporadic
• Outbreak vs. Sporadic Cases• 2004-2011: 1,084 cases reported to CDC via FoodNet• 56 (5.2%) only associated to outbreaks
– Little idea about the implicated foods for sporadic cases
• Some case characteristics (age, gender, illness severity) comparable to outbreaks
• Comparable implicated foods? – Few contaminated products will not lead to an outbreak
Interagency Food Safety Analytics Collaboration webinar, Jan 10th, 2014
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Outbreaks: shift in the implicated foods since 1998Year Cases Food Year Cases Food Year Cases Food1998 108 Frankfurters 2005 6 Unknown 2011 2 Undetermined
4 Frankfurters 3 Grilled chicken 2 Chive cheese and ackawi cheese
1999 6 Unknown 13 Deli meat 147 Whole cantaloupe4 Frankfurters 12 Mexican-style cheese 2 Mexican-style cheese
5 Deli meat 2006 2 Unknown 15 Aged, blue-veined cheese11 Pâté 2 Taco or nacho salad 2012 22 Ricotta cheese2 Deli meat 3 Cheese
2013 6 Soft ripened cheese2000 13 Mexican-style cheese 2007 5 Milk
2014 8 Mexican-style cheese
30 Deli meat 2008 5 Tuna salad5 Mexican-style cheese
2001 28 Deli meat 20 Sprouts 5 Sprouts2002 54 Deli meat 8 Mexican-style cheese 35 Caramel apple2003 3 Unknown
2010 8 Hog head cheese2015
10 Ice cream
12 Mexican-style cheese 2 Sushi rolls 30 Cheese
4 Undetermined
10 Pre-cut celery
6 Mexican-style cheese
CDC (2013). MMWR Morb Mortal Wkly Rep 62(22): 448-452.Cartwright et al., Emerg Infect Dis 19(1): 1-9.CDC website
Listeria Outbreaks and Incidence, 1983-2014
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
012345678
0123456789Total
Outbr...
Pre-PulseNet
0.369
Early PulseNet
2.311
Listeria Initiative
2.95.5
No. outbreaks Incidence (per million pop)
EraOutbreaks per
yearMedian cases per
outbreak
WGS8
4.5
Data are preliminary and subject to change
Slide: CDC via M. Wiedmann
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Overall: Stable number of cases since 2003
• Laboratory confirmed cases in FoodNet
CDC MMWR 2014 / 63(15);328-332
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Conclusions: Epidemiology
• Few cases, severe, mostly sporadic• Sharp decrease in the number of cases, then
stable since 2003• Evolving knowledge, linked to evolving tools
– More, smaller recognized outbreaks • Evolving food implicated in outbreaks
– Sporadic cases?
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LISTERIA IN READY-TO-EAT FOOD (AND ELSEWHERE)
L. monocytogenes: ubiquitous bacteria • Widely distributed in the environment
– Soil, water, vegetation• 15% Lm in preharvest env. (NY state)
– Manufacturing environment• persistent strains that have found a harborage site
within the facility where it may reside for years… • transient strains…
– Retail environment• idem • e.g. 241 retail establishments tested
– 60% positive (at least one positive sample)– 6.3% food-contact surface samples were positive– 17% of non food-contact surface samples were
positive » Milk crates: 34%! Floor drains: 28%!
Environment
Processing
Retail
Food
Strawn et al, 2013 Appl Environ Microbiol. 79(24):7618-27Hoelzer et al., J Food Prot 74(7): 1083-1095
Simmons et al. J Food Prot 77(11): 1929-1939
Commodities
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In Food: FSIS inspected facilities
Percentage of RTE meat and poultry products testing positive for L. monocytogenes in FSIS- inspected facilities, compared with incidence of listeriosis per 100,000, from CDC FoodNet surveillance
Interagency Risk Assessment: Listeria monocytogenes in Retail Delicatessens Technical Report (2013)Source data: FSIS and CDC
Year
1990 1995 2000 2005 2010
L. monocytogenes
ALLR
TE
Testing (%
Positives)
0
1
2
3
4
5
List
erio
sis
Inci
denc
e Pe
r 10
0,00
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6Testing PrevalenceListeriosis Incidence
In Food: survey data
* Preliminary results from phase I
FDA/ARS Survey* (2013)
(0.27%) (4.31%)
(0.76%) (4.70%)
(0.049%) (1.25%)
(1.04%) (2.36%)
Source: Food Advisory Committee Meeting Materials, September 29-30, 2014 13
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No-growth food?• Known limits
– pH less than or equal to 4.4– Water activity less than or equal to
0.92• Better knowledge of interactions
– Robust predictive microbiology models (most studied bacteria)
• Remaining issues– Heterogeneity
• within product, lot-to-lot
– Validation of challenge tests?
• see Powell, 2009, IJFM 136 10-17
Augustin and Carlier, 2000, IJFM 56: 53-70
Mejlholm et al, 2010, IJFM 141: 137-150
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Conclusions: L. monocytogenesin RTE food
• Ubiquitous bacteria widely distributed in the environment, manufacturing environment, retail environment– Frequently found on non food contact surfaces
• Decrease in the prevalence in food over the last decade(s)– FSIS inspected facilities– Other food– (decrease in the number of cases?)
• Growth-No growth boundary in practice?
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Listeria dose-response
Listeria monocytogenes Levels in Food (per serving)
Number of Servings(per year in the United States)
Number of Servings (per person per year)
0 3.3 1011 1300
1 to 1000 4,900,000,000 19
103 to 106 620,000,000 2.4
106 to 109 130,000,000 0.5
> 109 73,000,000 0.3
2,500 annual cases(Mead et al., 1999)1,600 annual cases(Scallan et al., 2011)
(FDA/FSIS, 2003)
Lots of bacteria
Few cases
ca. 1.8% RTE food contaminated (Gombas et al., 2003)Smoked seafood: prevalence: 4.3%, up to 105-106 CFU/g
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Listeria dose-response
• Probability of invasive listeriosis following the ingestion of Listeria is then– On average: very low– But function of
• Individual Susceptibility ++++• Strain Virulence ++
– But no Listeria monocytogenes is safe• Food vehicle ?• Dose
0 20 40 60 80
0.0
0.5
1.0
1.5
2.0
2.5
Age
Inci
denc
e ra
te
Individual Susceptibility
Non Hispanic womenFoodNet Data, 2004-2009
“Healthy” (less 65 year old, no known underlying condition)
1.0
65-74 year old 8.0
more 74 year old 20
Pregnant 116
Chronic Lymphocytic Leukemia 1,138
HIV/AIDS 55
Diabetes 1 44
Diabetes 2 5.4
Heart disease 5.4
Pouillot et al. 2014 Clin Infect Dis. 54 Suppl 5:S405-10.Goulet et al.2012 Clin Infect Dis. 54:652-60.
(per
100
,000
)
Virulence heterogeneity
• Listeria monocytogenes is one of the most studied intra-cellular pathogen
• Entry of L. monocytogenes into certain human epithelial cells is receptor mediated, – Depending on specific interactions between internalins on
the bacterial surface and their respective host cell receptors– Point mutations in the inlA gene can lead to virulence
attenuation
• Nevertheless, all Listeria monocytogenes should be considered as pathogen
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Dose-Response models
Hoelzer et al, 2011, Risk anal, 33 (9) 1568-81
Models basedon animal data
Model based on outbreak data
Models based on epi data
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
13
log10(Dose)
Pr(Il
lnes
s|do
se)
‘Average’
Virulent Strain A Less Virulent Strain B
Strain A, Susceptible Individual Strain B, Non Susceptible Individual
How far will we go?
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23
0 5 10 15 20
-8-6
-4-2
0
log10Dose
log 1
0P
rob
FDA 2015 dose-resposne model andbutter outbreak in hospitalized patients
DR for this specific outbreak as estimated from data
FDA 2015 DR for transplant organ patients, highly virulent strain, moderately virulent strain (this study)
PrimateDR
Established DR for Susceptible population, FAO/WHO 2004
Pouillot et al., Risk Analysis, 35(1):90-108, 2015
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Conclusions: Dose-Response• In order to explain the relatively high frequency of product contamination
and the relative rareness of the disease, one must assume that, “on average”, low dose equals low risk– FAO/WHO, 2004
• Refined models better characterize the variability in the dose-response: “on average”, low dose equals low risk, but in susceptible subpopulations, a relatively low dose may lead to a measurable risk for some individuals – Pouillot et al, 2015
• Animal models and outbreak data model would predict too many cases if applied as-is
• The variability in individual susceptibility and strain virulence maybe more important than the dose
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LISTERIA MONOCYTOGENES RISK ASSESSMENTS
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• FDA/FSIS 2003• Quantitative
Assessment of Relative Risk to Public Health From Foodborne Listeria monocytogenes Among Selected Categories of Ready-to-Eat Foods
• Dose Response considers strain variability and host susceptibility. Scaled to epidemiological data. Characterized uncertainty
• Risk: products that support growth
Decreased Risk per Annum
Dec
reas
ed R
isk
per S
ervi
ng
Clusters A and B Clusters C and D Cluster E Very High Risk
(Clusters 1-A, 1-B) Deli Meats Frankfurters (not reheated)
High Risk (Clusters 1-C, 1-D)
Pâté and Meat Spreads Unpasteurized Fluid Milk Smoked Seafood
Moderate Risk (Cluster 1-E)
No food categories Cluster 1
High Risk (Clusters 2-A, 2-B)
High Fat and Other Dairy
Products Pasteurized Fluid Milk Soft Unripened Cheese
Moderate Risk (Clusters 2-C, 2-D)
Cooked RTE Crustaceans
Moderate Risk (Cluster 2-E)
No food categories Cluster 2
Moderate Risk
(Clusters 3-A, 3-B)
No food categories
Moderate Risk (Clusters 3-C, 3-D)
Deli-type Salads Dry/Semi-dry Fermented Sausages Frankfurters (reheated) Fresh Soft Cheese Fruits Semi-soft Cheese Soft Ripened Cheese Vegetables
Low Risk (Cluster 3-E)
Preserved Fish Raw Seafood
Cluster 3
Moderate Risk
(Clusters 4-A, 4-B)
No food categories
Low Risk (Clusters 4-C, 4-D)
No food categories
Very Low Risk (Cluster 4-E)
Cultured Milk Products
Hard Cheese Ice Cream and Other Frozen Dairy Products
Processed Cheese
Cluster 4
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FSIS Risk Assessment for L. monocytogenes in Deli Meats (2003)
• Plant-to table probabilistic risk assessment built on FDA/FSIS 2003 risk assessment– Evaluated the number of illness
prevented and lives saved annually according to various processing interventions
• Led to Interim final rule– Alternative 1: Use of post-lethality
treatment AND antimicrobial agent/process
– Alternative 2: Use of post-lethality treatment OR antimicrobial agent/process
– Alternative 3: Use of sanitation procedures only
Source: FSIS
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FAO/WHO 2004: Risk assessment of L. monocytogenes in ready-to-eat food
• Exponential dose-response models– One for susceptible population, – One for non-susceptible population
• “The vast majority of cases of listeriosis are associated with the consumption of foods that do not meet current standards for L. monocytogenes in foods, whether that standard is zero tolerance or 100 CFU/g”
FAO/WHO (2004). Risk assessment of Listeria monocytogenes in ready to eat foods - Technical report.
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FDA/FSIS Interagency Risk Assessment: L. monocytogenes in Retail Delicatessens (2013)
• Sampling surveys and RA attribute most listeriosis cases from deli-meat to retail-sliced deli meat
• This RA evaluated the impact of cross-contamination, sanitation, growth in retail deli– Complex discrete event model– FAO/WHO dose response
• Key findings– Would explain some sporadic cases– Control Growth, notably through the use of
growth inhibitors– Contaminated products that do not support
growth can lead to a risk of listeriosis from cross-contamination of product that do support growth
Interagency Risk assessment: Listeria monocytogenes in retail delicatessens (2013)
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NEW DATA
Usual data to inform Listeria monocytogenes dose-response models are difficult to obtain
• Volunteers • Animal Models
– Validity of the animal model? • Hoelzer et al, 2012 Veterinary Research 43(1): 18
• Outbreak Data– Long incubation period -> Difficult to find leftovers
• Case report• Case control studies• Epidemiological Data
FDA Data Collection Efforts
• Celery Outbreak, TX, 2010– Limited prevalence and contamination level data– Data on underlying health issues– Growth studies
• Cantaloupe Outbreak, Multistate, 2011 – Limited prevalence and contamination level data– Growth studies
• Caramel Apple, Multistate, 2015– Growth studies
• Ice Cream, Multistate, 2015– Extensive prevalence and contamination data– Opportunity to assess exposure and underlying health issues
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The case of the caramel apples• Apple does not support growth (pH 3.2), • Caramel does not support growth
(low aw)• Caramel coated apple with a stick
support growth – Up to 7 log10 in few days at ambient
temperature • 35 illness including
– 11 associated with a pregnancy– 3 meningitis among otherwise healthy
children aged 5-15– (target population!)
CDC websiteBouvier, Science Translational Medicine 7 (311) pp. 311ec184 (2015)K. A. Glass et al., mBio 6, e01232-15 (2015).
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The case of ice-cream• 10 cases …
– 4 cases, observed in a single hospital, linked to one product of factory A (through milk shakes)
– 5 cases linked to a second factory (factory B)
• … over 5 years!• FDA obtained products from
factory A– Product that does not support
growth (frozen)– Observed levels of bacteria are
relevant to consumed levels
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Enumeration data
• “Product A”, from factory A – 2,290 samples of Product A tested all but 13 samples were positive (99.4% positive)
• Range: <0.03 MPN/g to > 208 MPN/gm– Highly consistent low contamination levels
• 15% below 1 MPN/gm• 58% below 5 MPN/gm• 77% below 10 MPN/gm
• 92% below 20 MPN/gm• 98% below 50 MPN/gm• 99.8% below 100 MPN/gm
– 4 samples > 100 MPN/gm**one >208 MPN/g (direct plating: 357 cfu/gm), two = 208 MPN/gm (direct plating: 142 cfu/gm and Non Available), and one 139 MPN/gm (direct plating: 177cfu/gm)
Chen et al, submitted; Chen et al, IAFP 2015
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Enumeration of L. monocytogenes in Different Lots of Product A
Average: 8 MPN/g
Chen et al, submitted; Chen et al, IAFP 2015
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Exposure data (preliminary) • Our estimates from product distribution records
– 4,000,000 to 33,000,000 contaminated servings sold to the population– 62,000 to 471,000 contaminated servings sold to pregnant women: no
case identified– 16,000 to 56,000 contaminated servings sold to highly susceptible
population 4 identified cases
• Corresponding dose-response model comparable to previous dose-response models developed from outbreaks– Other outbreaks: limited diffusion of products contaminated at
relatively high level– Here: large diffusion of products contaminated at low level
(Pouillot et al, in preparation)
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Ice cream Outbreak – Tentative Conclusions
• We’ll probably never get better data• A no-growth product, with a very low average level of contamination (8 cfu/g) did cause an
“outbreak”– It is likely that most patients were exposed to ice cream with < 100 cfu/g– A high dose can’t be excluded
• Growth in milk shake > few logs improbable but• “inoculation” of the shaker at each serving. Biofilm? Growth?
• The large distribution of a no-growth product, with a low average level of contamination (8 cfu/g) didn’t cause a massive outbreak
• The underlying health of the patient, cell-mediated immune status and medications may be more important than the dose
• Sufficient for risk management?
• Black Swan ? or White Swan?• Few products that support growth (e.g. cheese) -> Outbreak• Very large diffusion of a contaminated product that
does not support growth (ice-cream) -> Outbreak
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Conclusions: Listeria monocytogenes…
• The most studied foodborne bacteria
• A lot of questions remain unanswered
• Risk management in an uncertain world