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 populationNumber

of Casesof Disease

Time

Two Broad Types of Epidemiology:I descriptive epidemiology: examining the distribution of disease in a population, and observing the basic features of itsdistributionI 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