Download 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

Epidemiology derives from epidemic, a term
that provides an immediate clue to its subject
matter.

Originates from the Greek words epi (upon) +
demos (people) + logy (study of)

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)

Epidemiologists had the challenge of isolating a
single bacteria, virus, or parasite

The discipline of epidemiology underwent dramatic
changes in the first half of the 20th century.

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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Study of the health and disease of the “body
politic” – the population.
•
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?

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

Explains why and how health-related states
or events occur

Classic descriptors of how common a disease,
symptom, or problem is in a population

Incidence- measures the occurrence of new
disease in a population

Prevalence- measures the existence of
current disease in a population

Incidence: Fraction of a group initially free of
the condition that go on to develop it during
a given time period.
 How 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.

Incidence is calculated as the number of new cases
of a disease or condition in a specified time period
(usually a year) divided by the size of the
population under consideration who are initially
disease free.

Example:
 For example, the incidence of meningitis in the UK in
1999 could be calculated by finding the number of
new meningitis cases registered during 1999 and
dividing that number by the population of the UK.

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 dividing the
number of persons with the disease or condition
at a particular time point by 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.

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 time an event
occurs
 Epidemiology studies the number of times a
disease occurs
▪ It answers the question- How many?
▪ Epidemiology is a quantitative study

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)

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
Epidemic: outbreak of one specific disease in
excess of what would be normally expected
(W. Nile)
Pandemic: Epidemic affecting a large
number of people, many countries,
continents, or regions
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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

Agent factors + Host factors + Environmental
factors = Etiology of Disease
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When an infectious disease is contagious, or
capable of being communicated or
transmitted, it is called a communicable
disease

Communicable diseases spread through air,
water, food, and contact.
 Examples:
▪ HIV/AIDS
▪ Hanta virus
▪ Bird flu

Some — but not all — infectious diseases spread
directly from one person to another. Infectious
diseases that spread from person to person are
said to be contagious (communicable).
 Some infections spread to people from an animal or
insect, but are not contagious from another human.
▪ Lyme disease is an example: You can't catch it from someone
you're hanging out with or pass in the street. It comes from
the bite of an infected tick.