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Epidemiology
the study of the distributionand determinants of health-related states or events in specified populations, and the application of this study to control health problems.
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The 5 W’s?
- 1.Diagnosis or health event (what)
- 2.Person (who)
- 3.Place (where)
- 4.Time (when)
- 5.Causes, risk factors, & modes
- of transmission (why/how)
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Distribution
•Epidemiology is concerned with the frequency and pattern of health events in a population.
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Frequency
- not only the number of health events (# cases of meningitis or diabetes in a population), but also the relationship
- of that number to the size of the population.
- (rate)
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Pattern
- occurrence of health-related events by
- time, place, and person.
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Characterizing health events by time,
place, and person are activities of?
Descriptive epidemiology.
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Determinants
causes/factors that influence the occurrence of disease and other health-related events.
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Epidemiologists use analytic epidemiology
to provide the “Why” & “How” of event….
–think chain of infection
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Health-related states or events may
be anything that affects the well-being of a population.
–Amount of exercise
–Seat-belt use
–Genetic markers of disease risk
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Epidemiology is the study (scientific, systematic, data-driven) of the distribution
(frequency, pattern) and determinants
(causes, risk factors) of health-related
states and events (not just diseases) in specified populations (patient is community, individuals viewed collectively), and the application of this study to the control of health problems.
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Community/Population is focus of
epidemiology.
•Identifying exposure or source that causes illness
•Number of other persons who may have been exposed
•Potential for further spread in the community
•Interventions to prevent additional
cases or recurrences
•INDIVIDUAL (HCP) vs Collective Health focus (PH)
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•1850s – an anesthesiologist who studied the cholera outbreak in London, “father of field epidemiology”
John Snow
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Agent
- An animate or inanimate factor that must
- be present or lacking for a disease or condition to develop
- •Categories of causative agents:
- –Physical
- –Chemical
- –Nutrient
- –Biological
- –Psychological
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Physical agents
- Various mechanical forces or frictions
- that may produce injury or disease
- –Extremes in temperature
- –Radiation
- –Trauma
- –?Genetic?
- •Sometimes classified by itself
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Chemical agents
- Substances
- –Dust
- –Vapors
- –Fumes
- –Medicines
- –Liquids
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Nutrient Agents
- Dietary components whose absence or
- excess results in disease
- –Vitamins
- –Minerals
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All living infectious organisms
- –Insects
- –Worms
- –Protozoa
- –Bacteria
- –Viruses
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Psychological Agents
- Stressful circumstances in the
- environment
- –Fear
- –Anxiety
- -Prejudice
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Host
- A living species (human or animal)
- capable of being infected or affected by an agent
- –Genetic susceptibility
- –Immutable characteristics (sex, age)
- –Acquired characteristics (immunological
- status)
- –Lifestyle factors (diet, exercise)
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Enviroment
- All external to a given host or agent and
- that is influenced and influences the host/or agent
- –Climate
- –Plant and animal life
- –Human population distribution
- –Socioeconomic factors
- –Working conditions
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INFECTIOUS Agents can be classified in terms of their ability to produce disease in the
host
- •Infectivity
- •Pathogenicity
- •Virulence
- •Invasiveness
- •Toxigenicity
- •Antigenicity
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Organism’s ability to spread rapidly from
- one host to another host.
- –Influenza
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Pathogenicity
- The ability of an agent to cause disease
- after infection.
- •Measured as the proportion of infected
- persons infected by an agent who then experience clinical disease.
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Virulence
Ability to produce severe disease
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Invasiveness
Capability to spread and disseminate in the host.
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Toxigenicity
Capability to produce poisonous products (such as exotoxins)
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Antigenicity
Capability of stimulating the hostto produce an immune response (productionof antibodies or antitoxins)
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NON-INFECTIOUS Agents classified in terms of their ability to cause injury to biological
tissue in host:
- •Chemical (toxicity)
- •Physical (size and shape)
- •Psychological Stress (chronic or sudden onset)
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Reservoirs of the Agent
- •Agent’s habitat
- •Can be human, animals, insects, plants,
- soil, or inanimate matter in environment.
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Human reservoirs: Carriers
- •Persons who harbor infectious agents but
- have no overt signs or symptoms.
- •Sub-clinical infections, incubatory,
- convalescent, chronic.
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