PART 2: Microbiological Risk Assessment (MRA)

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UNIT 3 KEY STAGES IN THE PROCESS OF RISK
ASSESSMENT

• PART 2 Microbiological Risk Assessment (MRA)

Christine CEZARD (Unit co-ordinator) Anabel
VITAS Kofi Aidoo IUT A USTL Lille France
University of Navarra Pamplona
Spain Glasgow Caledonian University
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RISK ASSESSEMENT
_____________________________________________
Introduction
Identification and quantification of the risk
resulting from a specific use or occurrence of a
chemical, physical or microbiological agent,
taking into account possible harmful effects on
individual people or society of using the
agent in the amount and manner proposed and all
the possible routes of exposure
SCIENTIFIC PROCESS
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THE RISK ASSESSEMENT PROCESS
_____________________________________________
Introduction

• 1. Hazard identification
• 2. Hazard characterization
• 3. Exposure assessment
• 4. Risk characterization

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STEP 1. HAZARD IDENTIFICATION
______________________________________Hazard
identification
HAZARD a biological, chemical or physical agent
with the potential to cause an adverse health
effect (CODEX)
MICROBIOLOGICAL RISK ASSESSMENT (MRA) Emphasis
is given to the agent, the likelihood of
its association with food or water and
consequences of its presence
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______________________________________Hazard
identification
MICROBIOLOGICAL HAZARD IDENTIFICATION
Determination of pathogenic microorganisms
or microbial toxins, evaluating whether they
have the potential to cause harm when present
in food or water
STEP 1
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______________________________________Hazard
identification
WHICH microbiological hazards ?

• From the pathogen perspective (which agent
  bacteria, viruses, yeasts, moulds, algae,
  parasitic protozoa, their toxins)
• From the public health perspective (which
  illnesses in which categories of the population)
• From the product perspective (which products are
  enveloped)

STEP 1
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______________________________________Hazard
identification
Adapted from Brown, 2002
STEP 1
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______________________________________Hazard
identification
STEP 1
Adapted from Brown, 2002
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______________________________________Hazard
identification
STEP 1
Source ILSI Europe. Diane Benford.
http//europe.ilsi.org/file/ILSIcmRA.pdf
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______________________________________Hazard
identification
STEP 1
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______________________________________Hazard
identification
STEP 1
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______________________________________Hazard
identification
DATA USED FOR MICROBIOLOGICAL HAZARD
IDENTIFICATION?

• For many established food-and water-borne
  pathogens
• information available in scientific literature
• Public health and surveillance data
• Government agencies relating to the amounts,
  frequencies and sources of the microorganism
• For new emerging pathogens
• similar approaches to those for chemical hazards
  (clinical studies, epidemiological and animal
  studies)

STEP 1
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______________________________________Hazard
identification
EXAMPLE MICROBIOLOGICAL HAZARD IDENTIFICATION
Observations - It causes listeriosis in humans,
with symptoms including mild diarrhoea,
meningitis, septicaemia, abortion and
stillbirth. - Epidemiological evidence suggests
that most exposure is foodborne - Cases are
infrequent but 20 to 40 are fatal in
susceptible individuals. - Illness is associated
with only a few virulent strains. - Major risk
factors include immnosuppression, pregnancy and
age Hazard identification - Milk and dairy
products, particularly soft cheeses are
implicated in outbreaks of listeriosis
Listeria monocytogenes
STEP 1
Source ILSI Europe. Diane Benford.
http//europe.ilsi.org/file/ILSIcmRA.pdf
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STEP 2. HAZARD CHARACTERIZATION
____________________________________Hazard
characterization
Qualitative and/or quantitative evaluation of
the nature of the adverse health effects
associated with biological, chemical and physical
agents
For chemical agents a dose-response assessment
should be performed. For biological agents a
dose-response assessment should be performed if
the data are obtainable.
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____________________________________Hazard
characterization
To estimate the nature, severity and duration
of the adverse effects that may result from
ingestion of harmful microbiological agents
present in food or water
1. Characteristics of the microorganism 2.
Interaction of the microorganism with the food
matrix and the host 3. Dynamics of infection
and/or intoxication 4. The host, and the hosts
health status and predisposing factors
STEP 2
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____________________________________Hazard
characterization
1. Characteristics of the microorganism

• Determination of virulence of the strain (Factors
  that allow the organism to survive the passage
  through the stomach, the immunological defences
  and multiply (which agent bacteria, viruses,
  yeasts, moulds, algae, parasitic protozoa, their
  toxins).
• Transmission of the microorganism between
  individuals
• Changes with time (natural mutations)

STEP 2
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____________________________________Hazard
characterization
2. Interaction of the microorganism with the
food matrix and the host

• Enhanced survival could be associated with
• Increased stomach pH (due to age or use of
  antiacids)
• Decreased residence time in the stomach (rapid
  transit of liquids)
• Protection of the microorganisms from stomach
  acid by entrapment in liquid droplets or in
  highly buffered foods.

STEP 2
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____________________________________Hazard
characterization
3. Dynamics of infection

• Amount of cells ingested increasing levels of a
  pathogen in food at the time of consumption
  generally result in
• a greater proportion of the population becoming
  ill
• a decrease in incubation period
• possibly in the severity of disease in
  individuals.

STEP 2
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____________________________________Hazard
characterization
4. Host susceptibility

• Genetic factors that compromise the immune
  response
• Reduced immune status of vulnerable
  subpopulations such as premature infants, the
  elderly, pregnant women, individuals taking
  immunosuppressive drugs
• Concomitant infections
• Nutritional deficiencies, stress

STEP 2
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____________________________________Hazard
characterization
DOSE-RESPONSE ASSESSMENT

• Infection It is assumed that a single cell of a
  pathogen could result in infection (but his
  probability would be very low in Listeria
  monocytogenes 1/1014)
• Toxi-infection a threshold level of toxin will
  be required in order for adverse effects to occur
  (but, due to proliferation of pathogens in the
  body, it is not possible to associate a level of
  pathogen intake with production of a threshold
  level of toxin)

STEP 2
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____________________________________Hazard
characterization
DOSE-RESPONSE ASSESSMENT

• Foodborne disease analysis
• Food surveillance data
• Population characteristics surveys
• Animal trials
• Human volunteer studies

SOURCES OF INFORMATION
Mathematical models
STEP 2
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____________________________________Hazard
characterization
EXAMPLE MICROBIOLOGICAL HAZARD CHARACTERIZATION
Listeria monocytogenes
- Dose-response models (mathematical models) for
the normal (low risk population) and for
high-risk populations (including pregnant,
elderly or taking immunosuppressive drugs). -
The models determine the probability of human
listeriosis resulting from exposure to a certain
level of the agent.
Source ILSI Europe. Diane Benford.
http//europe.ilsi.org/file/ILSIcmRA.pdf
STEP 2
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STEP 3. EXPOSURE ASSESSMENT
____________________________________Exposure
assessment
Qualitative and/or quantitative evaluation of
the likely intake of biological, chemical or
physical agent via all relevant sources
Exposure is expressed in different terms for
chemical and microbiological agents For
chemical agents daily or weekly intake over a
lifetime For biological agents usually relates
to a single serving of contaminated food
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____________________________________Exposure
assessment
To describe the level of viable microorganisms
or microbial toxins in the food or drinking
water at the time of consumption
1. Characteristics of the pathogenic agent (its
resistance to heat, its growth range) 2. The
realistic association of the agent with a
particular foodstuff 3. The treatments that a
food undergoes from farm to fork (production,
processing, storing, handling) 4. The type of
treatment that the food undergoes
STEP 3
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____________________________________Exposure
assessment
Factors affecting microbiological exposure
assessment
5. Potential of cross-contamination with
pathogens from other foodsuffs 6. Preservation
factors in foodstuffs (temperature, pH, humidity,
atmospheric gases) 7. The nature of the
foodstuff itself and wether it allows or not the
growth or survival of the pathogen. 8. Consumer
use (handling and preparation)
STEP 3
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____________________________________Exposure
assessment
Data used for exposure estimation

• Growth models (laboratory studies about growth of
  the pathogen in different foods under different
  storage conditions). Mathematical modelling
  techniques.
• Challenge tests
• Storage tests (determination quantitative and
  qualitative of the pathogen in the food)
• Surveys

STEP 3
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____________________________________Exposure
assessment
EXAMPLE EXPOSURE ASSESSMENT
Listeria monocytogenes
1. Determination of L. monocytogenes in raw
milk Probability of milk being contaminated
67 Estimation of growth during storage in
farm, transport and storage by the
manufacturer 2. Cheese processing Estimation
of number of L. monocytogenes in one cheese vat
of 1000 litres Estimation of number of L.
monocytogenes in 250 g of cheese prepared from
2,2 litres of milk.
STEP 3
Source ILSI Europe. Diane Benford.
http//europe.ilsi.org/file/ILSIcmRA.pdf
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____________________________________Exposure
assessment
EXAMPLE EXPOSURE ASSESSMENT
Listeria monocytogenes
3. Estimation of intake Single serving 1/8 of
250 g cheese (31 g) Estimated an average of 50
servings per person/year Probability of
consuming contaminated cheese estimated
65 4. Investigation of alternative scenarios
Decreased contamination of cheese when cows with
L. monocytogenes are excluded
Source ILSI Europe. Diane Benford.
http//europe.ilsi.org/file/ILSIcmRA.pdf
STEP 3
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STEP 4. RISK CHARACTERIZATION
____________________________________Risk
characterization
Qualitative and/or quantitative estimation,
including attendant uncertainties, of the
probability of occurrence and severity of known
or potential adverse health effects in a given
population based on hazard identification,
hazard characterization and exposure assessment
Estimating how likely it is that harm will be
done and how severe the effects will be
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____________________________________Risk
characterization
Risk characterization provides the primary basis
for making decisions on how to manage the risk
in different situations

• Average probability of illness for adults from a
  single meal
• Average probability of illness for children from
  a single meal
• Change in probability of illness in children if
  processing or a raw material are changed
• Likelihood of disease per 100.000 individuals per
  year

STEP 4
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____________________________________Risk
characterization
The confidence in the risk assessment will
depend on the variability, uncertainty and
assumptions identified in all the previous
stages, and the weight of evidence and the type
of data on which it is based
STEP 4
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____________________________________Risk
characterization
EXAMPLE RISK CHARACTERIZATION
Listeria monocytogenes in cheese
1. Individual cumulative risk of listeriosis
Estimated from the probability of illness linked
to consumption of a single serving, number of
servings per person per year, the proportion of
Listeria strains t hat are virulent and the
probability of illness at a given dose.
Annual cumulative risk 2 to 64 per billion (for
low risk populations) 1000 to 72,000 per
billion (for high risk populations)
STEP 4
Source ILSI Europe. Diane Benford.
http//europe.ilsi.org/file/ILSIcmRA.pdf
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____________________________________Risk
characterization
EXAMPLE RISK CHARACTERIZATION
Listeria monocytogenes in cheese
2. Estimated incidence of listeriosis in a
country of 50 millions inhabitants Mean
number clinical cases of listeriosis 57 Mean
number of deaths 12 3. Effect of eliminating
milk from cows infected with L. monocytogenes
Estimates reduced to 11 cases and 2 deaths per 50
million inhabitants
STEP 4
Source ILSI Europe. Diane Benford.
http//europe.ilsi.org/file/ILSIcmRA.pdf