Transcript Epidemiology

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A public health science (foundation of public
health)
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Impacts personal decisions about our
lifestyles
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Affects government, public health agency
and medical organization policy decisions
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Epidemiology derives from epidemic, a term
that provides an immediate clue to its subject
matter.
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Originates from the Greek words epi (upon) +
demos (people) + logy (study of)
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Friis & Sellers 2009, defines epidemiology as
concerned with the distribution and
determinants of health and diseases,
morbidity, injuries, disability, and mortality
in populations.
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Application of this study to control and
prevent health problems in populations.
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In the past, main causes of death were due to a
single pathogen (disease causing microorganism or
related substance)
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Epidemiologists had the challenge of isolating a
single bacteria, virus, or parasite
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The discipline of epidemiology underwent dramatic
changes in the first half of the 20th century.
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A new kind of epidemiology came into being as a
discipline in the decades following the Second
World War variously referred to as “modern” or “risk
factor” epidemiology (Parascandola, 2011).
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The new epidemiology differed from earlier forms
of epidemiology in that it included a focus on
chronic rather than infectious diseases an emphasis
on identifying individual risk factors for disease, and
use of advanced quantitative methodology
(Parascadola, 2011).
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If you have an index card, raise your hand
 You have a “fake” disease
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What pattern do you notice? Compare those
that have the “fake” disease to those that
don’t.
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The first step when dealing with a disease
(epidemiology) is identifying what causes
the disease
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The next step would be to create a
hypothesis: Why is jewelry an indicator of this
“fake” disease?
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What is the next step in investigating a
disease?
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Study of the health and disease of the “body
politic” – the population.
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Basic science of public health
• What causes disease?
• How does disease spread?
• What prevents disease?
• What works in controlling disease?
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Descriptive
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Analytic
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Descriptive epidemiology involves
characterization of the distribution of healthrelated states or events by:
 Person – who?
 Place – where?
 Time – when?
 Clinical criteria – what?
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Describes frequency and patterns of
diseases/conditions
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Planning, conduction, and evaluation of
effective health education, screening,
prevention, and control programs
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Identifying and quantifying associations
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Testing hypotheses, and identifying causes of
health-related states or events
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Explains why and how health-related states
or events occur
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Ratio: Relationship between two numbers
 Example: males/females
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Proportion: A ratio where the numerator is included
in the denominator
 Example: males/total births
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Rate: A proportion with the specification of time
 Example: (births in 1999/population in 1999) x 1,000
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Classic descriptors of how common a disease,
symptom, or problem is in a population
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Incidence- measures the occurrence of new
disease in a population
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Prevalence- measures the existence of
current disease in a population
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Incidence: Fraction of a group initially free of
the condition that go on to develop it during
a given time period. (the # of new cases
during a certain time period)
 How is it measured?
▪ By identifying group of susceptible people (free of
disease) and examining them periodically in order to
discover and count new cases that develop during
interval.
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Incidence is calculated as the:
number of new cases of a disease or condition in a
specified time period (usually a year)
the size of the population under consideration who
are initially disease free.
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Example:
 110 new cases of malaria are detected in a community
during 2007. In June, the population of the community is
2200 people. What is the incidence rate of malaria?
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What is the incidence rate of malaria?
 110 cases/2200 persons =
 1
20
= 0.05 = 5 per 100 persons
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Prevalence: The fraction (proportion) of a
group processing a clinical condition at a
given point in time
 How measured?
▪ By surveying a defined population containing people
with and without the clinical condition at a single point
in time (snap-shot in time)
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The prevalence is calculated by:
number of persons with the disease or condition at a
particular time point
the number of individuals examined
 For example:
▪ In a study, 6139 individuals completed a questionnaire (were
examined). Of these 6139 people, 519 currently suffered
incontinence and so had the condition at the particular time
point of the study. Thus the prevalence of incontinence was
519/6139 = 0.085
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Prevalence is often expressed as a
percentage, calculated by multiplying the
ratio by 100.
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The above study expresses prevalence as a
percentage, thus the prevalence of
incontinence is 8.5% (or rounded is 9%)
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Frequency: the number of times an event
occurs
 Epidemiology studies the number of times a
disease occurs
▪ It answers the question- How many?
▪ Epidemiology is a quantitative study
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Distribution: Distribution of an event by
person, place and time
 Epidemiology studies distribution of disease
▪ It answers the question: who, where, and when?
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Determinants: Factors or events that are
capable of bringing about a change in
health(Friis & Sellers, 2009)
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Epidemiology studies what determines
health events
 It answers the question : how and why?
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Endemic: Persistent, usual, expected healthrelated state or event in a defined population over a
given period of time
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Epidemic: outbreak of one specific disease in
excess of what would be normally expected (W.
Nile)
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Pandemic: Epidemic affecting a large number of
people, many countries, continents, or regions
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Sporadic: refers to a disease that occurs
infrequently and irregularly
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Outbreak: carries the same definition of
epidemic, but is often used for a more limited
geographic area.
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Identifying causes of disease and the
mechanisms by which they spread remains a
primary focus of epidemiology
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Etiology: Science and study of the causes of
disease and their mode of operation
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The sum of all factors contributing to the
occurrence of the disease
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Agent factors + Host factors + Environmental
factors = Etiology of Disease