seminar presenatation PHCP 806

1. EPIDEMIOLOGIC INVESTIGATIONS
By
MUSA, Abbas
P16PHCP8016
DEPARTMENT OF CLINICAL
PHARMACY & PHARMACY PRACTICE
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2. Definition
 Epidemiology is the study of the
distribution and determinants of
health-related states or events in
specified populations, and the
application of this study to the control
of health problems.
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3. Types
 Descriptive epidemiology:
observational study of disease
occurrence
 Analytical epidemiology: observational
study of risk factor-disease
associations
 Experimental epidemiology:
experimental study of interventions
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4.  Endemic: applied to diseases which
exist in particular localities or among
certain races.
 Pandemic: an epidemic that has
spread so widely that very many
people in different countries are
affected.
 Examples Influenza pandemic of
1919–20 . AIDS/HIV.
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5. Dynamics of Dx Transmission
 Communicable diseases are
transmitted from the reservoir/ source
of infection to susceptible host
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6. Transmission pre-requisite
 Agent
 Source of agent
 Portable of exit from host
 Suitable mode of transmission
 Portable of entry suitable to agent
 Susceptible host
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8. Chain of transmission
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9. Chain of transmission
 There are three links in the chain of
transmission 1. Reservoir 2. Mode of
transmission 3. Susceptible host
 SOURCE & RESERVOIR • SOURCE • The
source defined as the “person, animal, object
or substance from which an infectious agent
passes or disseminated to the host”.
 15. • RESERVOIR • A reservoir is defined as
“any person, animal, arthropod, plant, soil or
substance in which an infectious agent lives
and multiplies , on which it depends primarily
for survival, and where it reproduces itself in
such manner that it can be transmitted to a
susceptible host”.
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10.  SOURCE “person, animal, object or
substance from which an infectious
agent passes or disseminated to the
host”.
 RESERVOIR “any person, animal,
arthropod, plant, soil or substance in
which an infectious agent lives and
multiplies , on which it depends
primarily for survival, and where it
reproduces itself in such manner that
it can be transmitted to a susceptible
host” 10Musa Abbas PHCP 806

11.  Types of reservoir 1. Human reservoir
2. Animal reservoir 3. Reservoir in non
living things
 HUMAN RESERVOIR The most
important source or reservoir of
infection for human is man himself.
 Human may be Case Carrier
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12. Cases
 CASES “ a person in the population having
the particular disease, health disorder or
condition under investigation”.
 •The presence of infection in host may be
◦ clinical case:- may be mild or moderate, typical
or atypical, severe or fatal. Mild cases may be
more important source of infection than severe
cases.
◦ Sub clinical cases also known as in apparent,
missed or abortive cases. The disease agent
may multiply in the host but does not manifest
itself by signs and symptoms. May be detected
only by laboratory tests.
◦ Latent infection • Infectious agent lies dormant
within the host without symptoms.
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13. CARRIERS
 A carrier is defined as an infected
person or animal that harbours a
specific infectious agent and serves as
a potential source of infection for
others.
 The elements in a carrier state are:-
◦ The presence of disease agent in the
body.
◦ The absence of recognizable signs and
symptoms
◦ Spread of disease agent in the discharges
or excretions. 13Musa Abbas PHCP 806

14. CARRIERS
 TYPE
A) Incubatory
B) Convalescent
C) Healthy
 DURATION
A)Temporary
B)Chronic
 PORTAL OF EXIT
A) Urinary
B) Intestinal
C) Respiratory
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16. Chain of Infection
 Etiological agent
 Source/Reservoir
 Portal of exit
 Mode of transmission
 Portal of entry
 Susceptible host
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17. Determinants of Disease
Outbreak
 Herd Immunity
 Resistance of a group to an attack by a disease to which
a large proportion of the members of the group are
immune
 If a large % of population is immune Þ entire population is
protected, not just those who are immune
 Why?
 – If a large % of population is immune then likelihood is
small that an infected person will encounter a susceptible
person and transmit the infection • More of the encounters
will be with other immune people • Important for
immunization programs – Do not need 100% coverage
immunization rates
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18.  Herd Immunity Necessary conditions:
◦ Disease agent must be restricted to a
single host species within which
transmission occurs
◦ Transmission must be relatively direct
from one member of the host species to
another
◦ Infections must induce solid immunity
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19.  Herd Immunity
 Works when:
◦ Probability of an infected person
encountering every other individual in the
population (random mixing) is the same
 Does NOT work when:
◦ An infected person interacts only with
people who are susceptible (no random
mixing); likely to transmit the disease to
those people
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20.  The Portal of Exit
 Route of escape of the pathogen from
the reservoir infectious agent enters
into surrounding reservoir env-transfer
to host at their portal of entry
 Examples: respiratory secretions, GI
blood exposure, breaks in skin
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22. Incubation Period
 The period of time after an infection is
established but before the first signs
or symptoms appear
 Different diseases generally have
different incubation times and
symptoms
 Therefore, can derive epidemic curves
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23. Out break
 The occurrence in a community or
region of cases of an illness with a
frequency clearly in excess of normal
expectancy
 The number of cases indicating an
outbreak vary
◦ infectious agent
◦ size and type of population exposed
◦ previous experience or lack of exposure
to the disease
◦ time and place of occurrence.
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24. Importance of outbreak
investigation
 Stop the current outbreak from
spreading
 „Prevent future similar outbreaks
 „Provide scientific explanation of the
event
 „Provide knowledge for the
understanding of the disease process
 „React to and calm public and political
concerns
 „Train epidemiologists
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25. Epidemiological Investigation
 Steps:
◦ Establish the existence of an outbreak
◦ Confirm the diagnosis
◦ Establish the case definition and count
cases
◦ Relate the outbreak to time, place and
person
◦ Determine who is at risk of becoming ill
◦ Formulate a tentative hypothesis
◦ Compare the hypothesis with the
established 25Musa Abbas PHCP 806

26. Establish the existence of an
outbreak
 Compare current information with
previous incidence in the community
during the same time of year to
determine if the observed number of
cases exceeds the expected.
Compare available information about
new cases with a predetermined
definition of an outbreak.
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27. Confirm the diagnosis
 Analyze clinical histories of cases and
have standard laboratory tests
performed to confirm or reject the
suspected diagnosis and to determine
the type of agent associated with the
illness (e.g.,bacterial, viral, other).
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28. Establish the case definition and
count cases
 Develop a case definition and
establish methods for identifying and
counting cases.
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29. Relate the outbreak to time,
place and person
 Characterize the outbreak according
to person, place or time by
interviewing known or selected cases
to determine common experiences,
such as when they became ill (time),
where they became infected (place)
and who they are (person).
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30. Determine who is at risk of
becoming ill
 Count cases and relate these counts
to the appropriate population to find
the group(s) at risk. Contact those
who can provide information on the
illness or about the environmental
circumstances that contributed to the
outbreak.
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31. Formulate a tentative hypothesis
 To explain the most likely
◦ cause, source and distribution of cases
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32. Compare the hypothesis with the
established facts
 The hypothesis will direct the course
of the investigation, and will be tested
by the various data gathered during
the investigation. Several successive
hypotheses may be required.
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33. Plan a detailed epidemiologic
investigation
 Descriptive
 Analytical
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34. Prepare a written report
 A written report should summarize the
investigation and be prepared as soon
as the investigation is completed. This
report should include the various
information listed in the example
referenced (refer to “Report of an
Investigation of an Outbreak”).
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35. Implement control and
prevention measures
 Effective control measures should be
developed using the evidence that has
been uncovered. Use the information
that has been collected during the
investigation to control the current
outbreak and also to prevent future
problems in the community. Initiate or
intensify surveillance of the disease and
agent. If imminent danger exists, control
measures should be initiated after a
tentative hypothesis has been formed.
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36.  Thank you for listening
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