Unit 3.

Food Safety

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 Presentation outline
• Definitions
• Objective of food hygiene
• Types of food borne illnesses
• Control and Prevention of Food Borne
Diseases
• Investigation of Outbreaks of Food-borne
Diseases

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 Definitions

Food satey:

• Means all conditions and measures necessary for

ensuring the safety, wholesomeness, and fitness
for consumption of food at all its stages from its
production, processing, storage, distribution,
preservation, and service. (WHO/FAO)

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 Definitions

Food Spoilage:
• Food spoilage is alteration of food in colour,
odour, taste, texture, consistency due to food
decomposition, decaying, rottening, and
fermentation.
• Food spoilage makes the food unsuitable,
unhealthy, undesirable for eating.

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 Definitions

• Food safety/hygiene is a science, which aims

to produce food which is safe for the consumer
and of good keeping quality.
• It involves the safe handling of food from the
time it has been produced until consumed:
(production to consumption/ Farm to fork).

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 Definitions

Food Adulteration:
• The intentionally and illegally addition of any
substance on food other than its genuine
component.

Misbranding/mislabeled:
• Giving a product or service a particular image
or brand identification.
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 Definitions

Mass Catering:
• The process, preparation and serving of
considerable amount of food to a large group
of people within a fixed time.

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 Objective of food hygiene

The collective goal of these programs is to

Protect food against infection

Insure wholesomeness of food

Meet consumer expectations

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Food safety: as essential public health priority

• More than 200 diseases are spread through food

• Food borne diseases are increasing worldwide

• Emerging problems are linked with food safety issues

• YOPI most affected

• Economic consequences for individuals, families,

communities, businesses and countries.

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 Categories of Food Safety Hazard
• Food safety is considering different types of hazards

• Microbiological hazards

• Chemical hazards

• Physical hazards

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 Biological hazards

•Infectious bacteria

•Toxin-producing organisms
Manifestations of these
hazards typically involve
•Moulds foodborne illnesses with
symptoms including
gastrointestinal distress,
•Parasites diarrhoea, vomiting, and
sometimes death.
•Virus
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 Chemical hazards

Different sources:
• Environmental pollutants such as lead, mercury,
polychlorinated biphenyls(PCBs), dioxins;
• Agricultural and veterinary practices such as pesticides,
fertilizers veterinary drugs;
• Food-processing and packaging techniques (e.g. the use of
solvent residues, nitrosamines, Bisphenol A)
• Naturally occurring toxins (fungal, algal toxins)
• Food additives (e.g. banned colour, preservative)

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Chronic sequelae  effects in the long term

The harmful effects may result from the constant exposure of

chemicals in food over time

Adverse health effects may include kidney and liver damage, fetal
developmental disruption, endocrine system disruption, immunotoxicity and
cancer

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 Physical hazards
• Either foreign materials unintentionally introduced to food
products (e.g. metal fragments in mince meat) or naturally
occurring objects (e.g. bones in fish) that are a threat to the
consumer.

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 Factors that affect microbial growth in foods

• To understand how to control micro-organisms, it is essential

to have some basic knowledge of the conditions required for
microbial growth.

• There are six factors required for the growth of micro-

organisms:

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1. Food/ a nutrient medium:

• MOs require sufficient and proper kinds of food for

growth and multiplication.

• Food of some sort, which may be a host tissue, blood,

plant matter, etc., is required.

• Food is a substrate for MOs. (Biochemical reactions

take place by action of MOs on food)

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• To grow and function normally, the MOs of
importance in foods require the following from the
nutrient medium:
– Water,
– Source of energy (carbohydrates, lipids)
– Source of nitrogen (proteins),
– Vitamins
– Minerals

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2. A suitable atmosphere/ Oxidation-Reduction (OR) Potential

•The OR potential is an indication of the oxidizing and

reducing power of the substrate.
•To attain optimum growth, some MOs require reduced
conditions; Others need oxidized conditions
•The presence or absence of oxygen or other gases may
encourage or discourage the growth of a particular type
of organism

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• Based on oxygen requirements MOs can be divided
into two:

– Those that require oxygen are called aerobes/

aerobic; (Pseudomonas species is an example).

– Those that can live and multiply in the absence of

oxygen are called anaerobes/ anaerobic (example
Clostridium species).

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3. Water requirement/ Moisture

• Water activity is defined as the ratio of water vapor

pressure of the food substrate to the vapor pressure of
pure water at the same temperature aw = p/po

• Water acts as a solvent to bring essential nutrients into

and remove metabolic waste products from the cell.
– Bacteria need quite a high amount of water, where as
yeasts and especially molds can tolerate low
availability of water.

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• The aw of a food describes the degree to which
water is "bound" in the food, its availability to
participate in chemical/biochemical reactions,
and its availability to facilitate growth of
microorganisms.
• The aw can be manipulated in foods by a number
of means, including addition of solutes such as
salt or sugar, physical removal of water through
drying or baking, or binding of water to various
macromolecular components in the food.
• Most microbes require an Aw higher than 0.91 for growth.

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4. A suitable temperature (T0)

• Temperature has dramatic impact on both the

generation time of an organism and its lag period.

• Optimal temperature for proliferation of most MOs is

from 140C to 400C,

• The lowest T0 at which MOs have been reported to

grow is -340C

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• At low temperatures, two factors govern the
point at which growth stops:
1) reaction rates for the individual enzymes in the
organism become much slower
2) low temperatures reduce the fluidity of the
cytoplasmic membrane, thus interfering with
transport mechanisms.
• At high temperatures, structural cell
components become denatured and
inactivation of heat-sensitive enzymes occurs.
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• With reference to To requirement, MOs are divided in
to three categories:
– Psychrophilic,
– Mesophilic,
– Thermophilic.

• Most pathogenic organisms belong to the

mesophilic category.

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A. Psychrophilic

• Grow best at low temperature

• Their optimum rage is from 100C to 200C
• Not pathogenic to humans
• Cause food spoilage at low temperatures
• Usually found in soil and water
• Examples include:
– Pseudomonas
– Moraxella-Acinetobacter
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B. Mesophilic

• Moderate T0 lovers

• Their optimum range is form 300C to 400C

• Most pathogenic organisms belong to this group

• Examples include:
– Most Lactobacilli

– Staphylococci

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C. Thermophilic

• Grow best at highT0.

• Their optimum ranges from 500C to 600C
• Usually found in thermal springs and similar places
• Non pathogenic to human beings
• Examples of thermophilic bacteria:
– Bacillus stearothermophilus
– Bacillus coagulans
– Lactobacillus thermophilus

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• Bacteria, molds, and yeasts each have some
genera with T0s optimal in the range
characteristic of thermophiles, mesophiles,
and psychrotrophs.

• Molds and yeasts tend to be less thermophilic

than do bacteria.

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5. pH( Potential Hydrogen)

• pH measures the degree of acidity and alkalinity of the

food.
• Most pathogenic MOs have the optimum pH range from
slightly alkaline to slightly acidic, around pH range of 6
to 8.
• Strong acids or strong bases do not favor bacterial
growth.
– For example, foods with high vinegar (acid) content do not spoil
as easily as other foods.

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• Yeasts grow best at pH 3 to 6.

• Majority of molds are favored by an acid pH.

• Thus low pH food (e.g. fruits) is spoiled by yeasts

and molds.

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7. Time

• MOs can multiply under optimal conditions every 20

minutes.
• Microbiological deterioration of food takes a
combination of time &suitable environment.
• Spoilage of food by MOs can only occur if enough time
is allowed for the multiplication of the organisms.
• Therefore, favorable conditions for bacterial growth must
be left short in time so that large numbers of bacteria
cannot grow.
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Table: Bacterial growth in relation to time Source: Modern food microbiology.
6 ed., 1970; and 14th ed.1992. By Jay. J. M)

O’clock Number of bacteria Time taken

12:00 1 0 minutes

12:20 2 20 minutes

12:40 4 40 minutes

13:00 8 1 hour

14:00 64 2 hours

15:00 512 3 hours

16:00 4096 4 hours

17:00 32768 5 hours

18:00 262144 6 hours

19:00 2,097,152 7 hours

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 Three types of food microorganisms

1. Beneficial microorganisms
(e.g., yeasts, lactic acid bacteria and probiotics)

2. Spoilage microorganisms
(through their growth and ultimately enzymatic action)

3. Pathogenic microorganisms

(intoxication and infection)

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 Microbial Growth Kinetics

A. Lag Phase

• The period of adjustment (or adaptation) to the environment,

with a slight decrease in microbial load due to stress

• Improved sanitation and hygienic practices

 Lowered initial counts of microbes

 Extended lag phase and next growth phase entry

• Reduced temperature or other preservation techniques

 Increases the “generation interval”

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B. Logarithmic Growth Phase

• Characterized by the duplication of components within each

cell, followed by prompt separation to form two daughter cells.

• The phase length may vary from 2 to several hours.

• Logarithmic growth rate can be affected by:

 The number of microorganisms and environmental factors, such as
nutrient availability and temperature

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C. Stationary Growth Phase

• The growth rate slows and reaches an equilibrium

Number of death ≈ Number of new cell

• Ranges from 24hrs. to >30 days depends on both

 the availability of energy sources for the maintenance of

cell viability

 the degree of pollution in (hostility of) the environment.

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D. Accelerated Death Phase
• Accelerated death rate is similar to logarithmic growth rate
• Ranges from 24 hrs. to 30 days but depends on
 Temperature
 Nutrient supply
 Microbial genus and species
 Age of the microorganisms
 Application of sanitation techniques and sanitizers
 Competition from other microbes

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E. Reduced Death Phase

• Nearly the opposite of the lag phase.

• The microbial population number is decreased to the extent

that the death rate decelerates.

• After this phase, the organism has been degraded, sterilization

has occurred, or another microbial population continues
decomposition.

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 Typical growth curve for bacteria
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 The effect of initial contamination and lag phase on the growth
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curve of microorganisms 42
 Foodborne Illness
• Food-borne disease is ‘any disease of an infectious or
toxic nature caused by or thought to be caused by the
consumption of food or water’.
• Foodborne illness is the sickness people experience
after consuming food and beverages that are
contaminated with pathogenic (disease-causing)
microorganisms, chemicals, or physical agents.

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 Classification of Foodborne Illness
1. Foodborne Infection
• A foodborne infection is caused by ingestion of food contaminated
by either viruses, bacteria or parasites, and occurs in one of two
ways:
I. Viruses, bacteria or parasites in ingested food invade and multiply
in the intestinal mucosa and/or other tissues.
II. Bacteria in ingested food invade and multiply in the intestinal tract
and then release a toxin or toxins that damage surrounding tissues
or interfere with normal organ or tissue function. This type of
infection is sometimes referred to as a toxin-mediated infection.
• Viruses and parasites are not able to cause a toxin-mediated
infection.

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Classification of Foodborne Illness
2. Foodborne Intoxication

• A foodborne intoxication is caused by ingestion of food already

contaminated by a toxin. Sources of toxin are:

 certain bacteria,

 poisonous chemicals (e.g., heavy metals like copper), or

 toxins found naturally or formed in animals, plants or fungi (e.g.,

certain fish and shellfish, certain wild mushrooms).

• Viruses and parasites are unable to cause intoxications.

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 The probability of infection and subsequent illness is a
function of:

I. the vulnerability of the host (e.g., age,

immune resistance),
II. the number of units of the infectious agent
ingested with food (e.g., viralparticles,
bacterial cells, parasitic cysts), and
III. the virulence or pathogenicity of the agent.

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Summary of Foodborne Infection and Foodborne Intoxication

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 Foodborne Illness Caused by Bacteria
• Pathogenic bacteria can cause illness when they or
their toxins are consumed with food.
• Bacterial contamination may occur in raw food, in
cooked food that has not been properly handled,
and on the surfaces of equipment and utensils that
have been contaminated by raw animal foods,
humans, or pests such as insects and rodents.
• In addition, certain food products require time and
temperature control to limit the growth of
pathogenic microorganisms and toxin formation.
• These items are called potentially hazardous
foods (time/temperature control for safety
foods).
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 Foodborne Illness Caused by Spore-
Forming Bacteria
• Spores are inactive or dormant forms of bacterial
cells that enable the organism to survive when its
environment is too hot, cold, dry, or acidic or
when there is not enough food.
• Bacteria that survive as spores can avoid being
killed by typical measures taken against them
(such as heating), and multiply in more active
forms on the food that humans consume.
• Examples include clostridium perfringens
(diarrhea and cramps) and clostridium botulinum
(botulism).

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 Foodborne Illness Caused by Non-
Spore-Forming Bacteria
• Many types of bacteria exist only as vegetative
cells and do not form spores. Vegetative
bacterial cells are easily destroyed by heat and
can be effectively controlled by such processes
as cooking and pasteurization.
• Examples include Shiga Toxin–Producing E.
Coli, listeria monocytogenes (listeriosis),
salmonella, and staphylococcus aureus
(staphylococcal food poisoning).

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 Foodborne Illnesses Caused by Viruses
• The Hepatitis A virus causes a liver disease called
infectious hepatitis. It is usually spread via the
fecal-oral route and can contaminate food in
production plants.
• Noroviruses are a group of viruses that cause the
“stomach flu,” or gastroenteritis, in people. People
can become infected by eating food or drinking
liquids that are contaminated with a norovirus, by
touching surfaces or objects contaminated with a
norovirus and then placing their hands in their
mouth, and by having direct contact with another
person who is infected and showing symptoms.
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 Foodborne Illnesses Caused by
Parasites
• Anisakis spp. are roundworms found in some species of
fish. Humans are exposed to this parasite when they eat
parasite-infested fish. Symptoms include coughing if
worms attach in the throat, vomiting and abdominal pain
if worms attach in the stomach, or sharp pain and fever if
worms attach in the large intestine.
• Cyclospora cayetanensis is a parasite that has been
associated with fresh fruits and vegetables contaminated
at the farm. The parasite is passed from person to person
by fecal-oral transmission. handling. Symptoms of
cyclosporiasis include watery and explosive diarrhea, loss
of appetite, and bloating.

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 Time of onset, symptoms, cause and
duration of foodborne illness

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 Time of onset, symptoms, cause and
duration of foodborne illness

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Examples of Chemical Contaminants of
Foods

• Food allergens can pose a serious health risk to

children and adults who are sensitive to these
substances.
• 5 to 8 % of children and 1 to 2 % of adults are
allergic to certain chemicals found in foods and
food ingredients.
• Food allergens cause a person’s immune system to
overreact and may result in such symptoms as
hives, swelling of the lips and tongue, difficulty
breathing, vomiting, cramps, and diarrhea. In
severe situations a life-threatening allergic reaction
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Examples of Chemical Contaminants of
Foods
• Accidental/ deliberate addiction of chemicals
in foods
• Poisoning of animal tissues
• Plant poisoning

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a. Mushroom Poisoning:

• Many species of mushrooms/fungi are useful to humans as

food.

• Certain species of mushroom, such as Amanita phalloides and

Amanita muscaria are able to produce phalloidine and other
alkaloids which are poisonous in nature.

• Cooking has no effect on the poison.

Incubation period:

• About 15 minutes to 15 hours.

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b. Ergotism
• Some fungi that grow on crops such as rye, wheat, barley etc.
produce a toxin called ergot which is poisonous to humans.
• Ergot is produced by a parasitic fungus called Claviseps
purpurea.
• Ergotism is a crippling and gangrenous disease which affects
different areas of the body.
• The onset of symptoms is gradual; occurring after prolonged
and several consumption of the poison in cereal grains.
• Several outbreaks have occurred in the world, and in Ethiopia
there are records of such outbreaks that occurred in Wollo and
Arssi areas.
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C. Mycotoxins
• Mycotoxins are compounds produced by a wide range of fungi
that are toxic to humans and animals.
• The acute diseases caused by Mycotoxins are called
mycotoxicosis.
• Aflatoxin, one type of Mycotoxin, may cause liver cancer,
liver damage, intestinal and peritoneal hemorrhaging resulting
in death.
• Mycotoxins may enter the food by:
– Direct contamination, resulting from mold growth on the food
– Indirect contamination by use of contaminated ingredients or;
– The consumption of foods containing Mycotoxin residues.

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d. Other poisonous plant foods:
• Neurolathyrism (Lativa sativus or ‘’Guaya’’)
• Enkirdad

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Control and Prevention of Food Borne Diseases

• The CDC has identified several risk factors as

primary contributors to foodborne disease outbreaks;
these factors are therefore important focus areas for
food safety programs.
 Improper holding temperatures
 Poor personal hygiene
 Improper cooking temperatures
 Foods from unsafe sources
 Contaminated equipment and cross-contamination

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 Control and Prevention of Food Borne Diseases
• Among several factors that are commonly found to be the
cause of largely preventable foodborne outbreaks such as

1. Improperly refrigerated food

2. Improperly heated or cooked food

3. Food handlers who practice poor hygiene

4. Lapse of a day or more between preparing and serving food

5. Introduction of raw or contaminated materials into a food

that will not undergo further cooking

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6. Improper storage of foods at temperatures ideal for bacterial
growth

7. Failure to properly heat previously cooked foods to

temperatures that will kill bacteria

8. Cross-contamination of ready-to-serve foods with raw foods,

contaminated utensils, or machinery, or through the
mishandling of foods

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 The 10 golden rules of WHO for safe food

1. Choose foods processed for safety

2. Cook foods thoroughly
3. Eat cooked foods immediately
4. Store cooked foods carefully
5. Reheat cooked foods thoroughly
6. Avoid contact between raw and cooked food
7. Wash hands repeatedly
8. Keep all kitchen surfaces meticulously clean
9. Protect food from insects, rodents and animals
10. Use safe water

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 Food Preservation Methods

• Many microbes including the pathogens several important

characteristics, making it easier to develop common and
effective control measures against them.
• The major food preservation techniques can be categorized as
I. Slowing down or inhibiting chemical deterioration and
microbial growth
II. Directly inactivating bacteria, yeasts, molds, or enzymes
III. Avoiding recontamination before and after processing

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 Investigation of Outbreaks of Food-borne Diseases

Protecting the public from foodborne illness depends on

 rapid detection of outbreaks

 thorough knowledge of the agents and factors responsible

for foodborne illness.

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 The purposes of a foodborne illness investigation
 Determine the cause of the outbreak, including the
etiologic agent, and verify that the agent is foodborne.
 Detect all cases, the food(s) or beverages involved in the
transmission
 Environmental conditions and food-handling practices
that may have contributed to the transmission of the
agent.
 Control the outbreak, and prevent additional cases from
occurring.
 Document foodborne disease occurrence to improve the
knowledge of foodborne disease causation.
 Correct poor food-handling practices and provide training
to prevent similar occurrences.
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 Steps Investigation of Outbreaks of Food-borne
Diseases

• Although every outbreak is unique, the investigative

process generally follows these nine steps

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1. Obtain a description of food items and secure any leftover
food items.

 If the outbreak is associated with a particular event, acquire

a list of all food and beverages consumed at the event.

 If the outbreak is linked with a particular food

establishment, obtain a copy of the menu or product list.

 Determine if leftovers are available from the event. If so,

make sure they are collected, labeled, and stored at the
proper temperature and where they will not be discarded.

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2. Gather basic data

 Obtain clinical and three-day food histories for the ill

people through personal interviews or from medical
personnel.

 This involves collecting information about the food

consumed by the victim within the seventy-two hours prior
to the onset of symptoms.

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3. Formulate an initial hypothesis and case definition

 The initial case definition is based on facts about time,

place, person, clinical signs, and mode of transmission.

 This tentative hypothesis is used to direct the investigation;

however, it should not be too restrictive.

 Focusing too closely on one hypothesis can exclude

potentially important cases or events.

 Case definitions can change as the investigations

progresses.

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4. Collect clinical specimens for testing
 Determine if any clinical specimens have been collected by
health care providers and obtain the results of any tests.
 If specimens were collected, contact the reference laboratories
and have them save the specimens, if possible, for further
testing.
 When specimens have not yet been collected, investigators
should attempt to collect clinical specimens, first, from the
people who are currently ill and, second, from those who were
recently ill.
 Specimens should also be collected from food handlers who
were ill before the outbreak as well as from those who were
asymptomatic.
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5. Develop a questionnaire
 A standardized questionnaire is developed, using the initial case
definition, food item description, and clinical data. This tool is
used to collect
o Exposure data (time and place of exposure, approximate number exposed)
o Patient information (name, address, telephone number)
o Patient demographics (age, gender, and so forth)
o Illness history (whether subject is ill or well, any underlying conditions,
medications)
o Clinical data (signs and symptoms, onset date and time, recovery date and time)
o Medical attention sought (provider, sample collection, test results, treatment)
o Contact with other ill individuals
• It is extremely important to interview people who are well in
addition to those who are ill.
• The cause of illness can be identified only by comparing the
exposures (foods eaten) of those who are ill (cases) and of those
who are not (controls).
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6. Analyze the questionnaires.

 This is generally accomplished using a cohort or case

control study format.

 Analyze the data to identify differences in exposure

frequencies between cases and controls to confirm or refute
the hypothesis.

 As data from questionnaires are analyzed, it may be

necessary to modify the course of the investigation by
formulating a new hypothesis or case definition.

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7. Conduct an environmental investigation.

• The primary objective of the environmental investigation is to

determine what specific factors may have contributed to the
illness or outbreak and, if discovered, assure that they are
corrected.
1. Inspecting the food establishment

2. Collecting food samples

3. Facilitating enteric collections

4. Conducting a HACCP risk assessment on implicated foods

5. Initiating corrective or enforcement actions

6. Writing a report or summary

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8. Implement control measures
Control measures may include
 Providing post exposure prophylaxis to control the spread
of the disease
 Recalling or destroying food
 Making a public announcement of the outbreak
 Providing educational information
 Closing a food establishment to stop the ongoing spread of
disease
 Recommending antibiotic treatment or exclusion from
work or child care or other measures

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9. Summarize the investigation

 It is important to prepare a document that summarizes the

conditions and causes of the outbreak in order to prevent
future occurrences.

 This summary also serves as the public record of the

outbreak.

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