descriptive epidemiology ahmed mandil prof of epidemiology ksu college of medicine
TRANSCRIPT
Descriptive Epidemiology
Ahmed Mandil Prof of Epidemiology
KSU College of Medicine
Headlines Definition of Health Definition of Epidemiology Uses and Applications of
Epidemiology Descriptive versus Analytical
Epidemiology Epidemiological triads Related disciplines
Definition of Health
A state of complete physical, mental and social well-being, and not mere absence of infirmity (WHO, 1945)
Definition of Epidemiology
Epidemiology may be defined as: the study of distribution and determinants of health-related states or events in specified populations; and the application of this study to control of health problems (Last, 2000)
Uses and Applications of Epidemiology
- Establishing etiological hypothesis (causation)
- Studying natural history of disease
- Describing health status of populations
- Evaluating interventions
Establishing etiological hypothesis (causation)
This includes the study of the different factors (genetic / environmental / interaction between both), which may be responsible for ill health. This includes investigation of causes of communicable diseases, as well as risk factors for non-communicable diseases and injuries. All this can lead to identification of the most effective preventive methods, which have the overall goal of improving the health of populations.
Studying natural history of disease
This includes the study of the course and outcome (i.e. natural history) of diseases (in individuals and groups). This includes following up the affected people from the time of exposure, through subclinical stages; appearance of signs and symptoms (clinical disease); and final outcome (recovery, chronicity, disability, death)
Describing health status of populations
Epidemiology is also often used to describe the health status of populations groups. Knowledge of disease burden (morbidity, mortality) in populations is essential for health authorities, which seek to use limited resources to the best possible effect by identifying priority health programmes for prevention and care.
Evaluating Interventions
In addition to investigating etiological hypothesis, studying natural history of diseases, describing health status of population groups, epidemiologists have become involved in evaluating interventions. This inlcudes evaluating the effectiveness and efficiency of health promotion and educations programmes; preventive measures as well as public health services including management schemes.
What Is The Unique Skill Of Epidemiologists?
MEASURING DISEASE FREQUENCY IN
POPULATIONS
Measuring Disease Frequency Has Several Components
Classifying and categorizing disease
Deciding what constitutes a case of disease in a study
Finding a source for ascertaining the cases
Defining the population at risk of disease
Defining the period of time of risk of disease
Obtaining permission to study people
Making measurements of disease frequency
Relating cases to
population and time at risk
Two Broad Types of Epidemiology
Examining the distribution of a disease in a population, and observing the basic features of its distribution in terms of time, place, and person.
Typical study design:
community health survey (approximate synonyms - cross-sectional study, descriptive study)
Testing a specific hypothesis about the relationship of a disease to a putative cause, by conducting an epidemiologic study that relates the exposure of interest to the disease of interest.
Typical study designs: cohort, case-control
DESCRIPTIVE EPIDEMIOLOGY ANALYTIC EPIDEMIOLOGY
Epidemiological Triads
Descriptive Epidemiology Triad:
Person Place Time
Analytical Epidemiology Triad:
Agent Host Environment
The Basic Triad Of Descriptive Epidemiology
THE THREE ESSENTIAL CHARACTERISTICS OF DISEASE WE LOOK FOR IN DESCRIPTIVE EPIDEMIOLOGY:
TIME PLACE PERSON
Time
Changing or stable?
Seasonal variation.
Clustered (epidemic) or evenly distributed (endemic)?
Point source or propagated.
Time Trends Point source (e.g. food-borne outbreaks),
in terms of hours / days Seasonal - cyclicity (e.g. common cold,
influenza), in terms of months Propogative (e.g. water borne epidemics),
in terms of weeks / months Secular (e.g. morbidity / mortality of non-
communicable diseases), in terms of years Cluster in time / place
Place Geographically restricted or
widespread (pandemic)? Relation to water or food supply
(clusters: multiple / one) Residence (rural, urban, sub-urban) Weather (temperature, humidity) Natural / political
Person
Age
Socio-economic status
Gender
Ethnicity/Race
Behavior
Descriptive Epidemiology Is A Necessary Antecedent Of Analytic Epidemiology
To undertake an analytic epidemiologic study you must first:
Know where to look Know what to control for Be able to formulate hypotheses
compatible with laboratory evidence
A COMMON ERROR IN EPIDEMIOLOGY IS MOVING TO ANALYTIC EPIDEMIOLOGY WITHOUT HAVING A SOLID BASE IN THE DESCRIPTIVE EPIDEMIOLOGY OF THE CONDITION.
The Basic Triad Of Analytic Epidemiology
THE THREE PHENOMENA ASSESSED IN ANALYTIC EPIDEMIOLOGY ARE:
HOST
ENVIRONMENTAGENT
AgentsAgents
Biological (micro-organisms) Physical (temperature, radiation,
trauma, others) Chemical (acids, alkalis, poisons,
tobacco, others) Environmental (nutrients in diet,
allergens, others) Psychological experiences
Host Factors
Genetic endowment
Immunologic state
Age
Personal behavior
Environment Crowding Atmosphere Modes of communication – phenomena
in the environment that bring host and agent together, such as: Vector Vehicle Reservoir
Epidemiologists are required to have some knowledge of the disciplines of:
• Public health, because of the emphasis on disease prevention.
• Clinical medicine, because of the emphasis on disease classification and diagnosis.
• Pathophysiology, because of the need to understand basic biological mechanisms in disease.
• Statistics, because of the need to quantify disease frequency and its relationships to antecedents.
• Social sciences, because of the need to understand the social context in which disease occurs and presents.
Further Reading Porta M. A dictionary of epidemiology. 5th
Edition. Oxford, New York: Oxford University Press, 2008.
Gordis L. Epidemiology. 4th edition. Philadelphia, Pennsylvania: Elsevier Science, 2008
Beaglehole R, Bonita R, Kjellstrom T. Basic epidemiolgy. 2nd edition. Geneva: World Health Organization, 2006
Paneth N. Introduction to epidemiology. University of Pittsburgh.