epidemology

FOURTH YEAR

Epidemiology
Dr. Areej Mothanna

A Modern Definition

Study of the occurrence and distribution of health-related diseases or events in specified populations, including the study of the determinants influencing such states, and the application of this knowledge to control the health problem
(Porta M, Last J, Greenland S. A Dictionary of Epidemiology, 2008)

Uses of Epidemiology

To study the cause (or etiology) of disease(s), or conditions, disorders, disabilities, etc.
determine the primary agent responsible or ascertain causative factors
determine the characteristics of the agent or causative factors
define the mode of transmission
determine contributing factors
identify and determine geographic patterns


Uses of Epidemiology
To determine, describe, and report on the natural course of disease, disability, injury, and death.
To aid in the planning and development of health services and programs
To provide administrative and planning data

The Epidemiology Triangle

Time

Epidemiologic triad

Host

Agent
Environment
Biological agents
Physical agents
Chemical agents
Nutrient agents
Mechanical agents
Social agents
Physical environment
Biological environment
Social environment
Demographic characteristics
Biological characteristics
Socioeconomic characteristics


The Epidemiology Triangle
The agent is the cause of the disease
Can be bacteria, virus, parasite, fungus, mold
Chemicals (solvents), Radiation, heat, natural toxins (snake or spider venom)
The host is an organism, usually human or animal, that harbors the disease
Pathogen disease-causing microorganism or related substance
Offers subsistence and lodging for a pathogen
Level of immunity, genetic make-up, state of health, and overall fitness within the host can determine the effect of a disease organism can have upon it.

The Epidemiology Triangle

The environment is the favorable surroundings and conditions external to the human or animal that cause or allow the disease or allow disease transmission
Environmental factors can include the biological aspects as well as the social, cultural, and physical aspects of the environment
Time accounts for incubation periods, life expectancy of the host or pathogen, duration of the course of illness or condition.

Endemic, Epidemic and Pandemic

Endemic - The habitual presence (or usual occurrence) of a disease within a given geographic area
Epidemic - The occurrence of an infectious disease clearly in excess of normal expectancy, and generated from a common or propagated source
Pandemic - A worldwide epidemic affecting an exceptionally high proportion of the global population

Number of Cases

of Disease
Time


Two Broad Types of Epidemiology:
I descriptive epidemiology: examining the distribution of disease in a population, and observing the basic features of its
distribution
I analytic epidemiology: investigating a hypothesis about the cause of disease by studying how exposures relate to disease

Descriptive vs. Analytic Epidemiology

Descriptive
Used when little is known about the disease

Rely on preexisting data

Who, where, when

Illustrates potential associations

• Analytic
• Used when insight about various aspects of disease is available
• Rely on development of new data
• Why
• Evaluates the causality of associations
Both are important!


The End