OUTBREAK

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OUT-BREAK

• Paradorn 4418714
• Kraileark 4518583

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What is an outbreak ? Occurrence of
more cases of disease than expected in a given
area among a specific group of people over a
particular period of time
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Why investigate outbreaks? Stop the outbreak
Understand what happened and why Prevent
future outbreaks Improve our knowledge
Improve surveillance and outbreak detection
Training
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In investigating an outbreak, speed is
essential, but getting the right answer is
essential, too. To satisfy both requirements,
epidemiologists approach investigations
systematically, using the following 10
steps         1 .Prepare for field work
        2. Establish the existence of an
outbreak         3. Verify the diagnosis
        4. Define and identify cases        
5. Describe and orient the data in terms of time,
place, and person         6. Develop hypotheses
        7. Evaluate hypotheses         8.
Refine hypotheses and carry out additional
studies         9. Implement control and
prevention measures         10. Communicate
findings
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Figure 2. Probable cases of severe acute
respiratory syndrome, by reported source of
infection - Singapore, February 25-April 30, 2003
(from MMWR 52 405-11)
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Attack Rates by Items Served
at a Church Supper, Oswego,
New York, April 1940 
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Infection and intoxication
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  Action of Food infection Food infection
occurs when food contains a large number of
living harmful bacteria which grow in the human
intestinal tract.Common symptoms are an upset
stomach with violent diarrhea, cramps, fever,
nausea and vomiting.Symptoms usually occur
between 4 to 48 hours, lasting from 2 to 4 days
(death has even occurred).Infections usually
take longer than intoxications before the
symptoms appear, and the illness will take longer
to disappear.
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Action of Food
intoxication Food intoxication occurs when
bacteria grow in food and give off a waste
product called a toxin (poison).Toxins can also
cause tissue damage in the intestinal tract,
while some will affect the nervous
system.Symptoms vary (violent nausea and
vomiting, headache, dizziness and cramps).The
illness could be one or a combination of these
symptoms.The illness may last for several days
and could be fatal.Symptoms are usually severe
and occur quickly from 1 to 8 hours after eating.
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Staphylococcus Bacteria in the genus
Staphylococcus are pathogens of man and other
mammals. Traditionally they were divided into two
groups on the basis of their ability to clot
blood plasma (the coagulase reaction). 1. The
coagulase-positive staphylococci constitute the
most pathogenic species S aureus. 2. The
coagulase-negative staphylococci (CNS) are now
known to comprise over 30 other species.
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Description and Morphology - Gram positive -
Spherical cell - Cells arranged in irregular
clusters - Non-motile - Nonsporeforming -
Facultative anaerobe - S. aureus is pigmented
yellow-gold on solid media. - Normal flora of
humans found on nasal passages,skin and
mucous membranes - Pathogen of humans, causes a
wide range of suppurative infections, as well
as food poisoning and toxic shock syndrome 
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Coagulase test The coagulase enzyme
is an extracellular protein which binds to
prothrombin in the host to form a complex called
staphylothrombin. The protease activity
characteristic of thrombin is activated in the
complex, resulting in the conversion of
fibrinogen to fibrin. This is the basis of the
tube coagulase test, in which a clot is formed in
plasma after incubation with the S aureus
broth-culture supernatant.

S aureus and S intermedius are
coagulase positive. All other staphylococci are
coagulase negative. Coagulase-negative
staphylococci are normally less virulent and
express fewer virulence factors.
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Staphylococcus aureus toxin Time for symptoms to
appear 1-6 hours Symptoms Nausea
Vomiting, diarrhea, abdominal pain Associated
foods Foods that require considerable handling
during preparation and that are kept at slightly
elevated temperatures after preparation (salads,
cream pastries).
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Pathogenesis
of S. aureus infections
FIGURE 3. Sites of infection and
diseases caused by Staphylococcus aureus
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Gastroenteritis
is the irritation and inflammation of the
digestive tract. This condition may cause
abdominal pain, vomiting and diarrhea. Severe
cases of gastroenteritis can result in
dehydration. In such cases, fluid replacement is
the primary factor in treatment. All ages and
both sexes may be affected yet the most severe
symptoms are experienced by infants and those
individuals over sixty years old. The use of
certain drugs such as aspirin, antibiotics or
cortisone drugs may increase risk for this
condition.
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The symptoms of gastroenteritis
---abdominal cramps
---nausea and vomiting
---diarrhea ---loss of
appetite ---weakness
---fever or chills
---dehydration
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Staphylococcal
enterotoxin An enterotoxin is a toxic
substance produced by certain bacteria. The toxin
is released into your intestines, causing
gastrointestinal symptoms such as cramps and
diarrhea. S. aureus can produce foodborne
poisoning by the production of staphylococcal
enterotoxins (SEs), of which eight have
previously been identified SEA, SEB, SEC1, SEC2,
SEC3, SED, SEE and SEH. However, the analysis for
these enterotoxins in Staphylococcus-related
foodborne outbreaks have indicated that
additional un-identified enterotoxins may exist.
SEA SED are most frequently associated with
food poisoning, presumably because strains
producing these toxins can produce them over a
wider range of growth conditions. SEB SECs
share antigenic sites, as do SEA, SED, SEE
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Conditions Affecting Enterotoxin
Production Nutritional Factors. Mg, Fe, PPi,
or K. pH Levels. optimum pH levels for
production of SEA SEB and SEC appear to be
between 6.8-7.2. Temperature. Generally,
temperatures higher than those for optimal growth
of the bacterium are optimal for production of
enterotoxin. Sodium Chloride. enterotoxin
production is inhibited at salt levels above 5
NaCl. Water Activity. S. aureus can also
tolerate the addition of other chemicals which
effect a reduced water activity
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Staphylococcal enterotoxin detection 1.Chromatog
raphic Separation of Toxin from Foods for
Micro-Slide Double Diffusion 2. Microslide gel
double diffusion assay.