Community Health Nursing Course Epidemiologic Process"

Learning Objectives:
1. Define epidemiology
2. Discuss the basic epidemiological concepts
3. Summarize the steps of epidemiological process and investigation
Definition of Epidemiology –
It is "concerned with the distribution and determinants of health and disease, morbidity, injuries, disability and morbidity in populations" (Friis & Sellers, 2009, p. 6).
Allender (2014), page. 217
Concepts Basic to Epidemiology
Host, Agent, and Environmental Model Relationship-
Disease results from a complex interaction between man, agent and the environment. This interaction is frequently referred to as epidemiological triangle. Health is maintained when the host-agent-environment variables are in a state of equilibrium. Disease occurs when there is a change in any one of the three variables that disturbs the state of equilibrium.
Allender (2014), page. 220
These variables are defined as follows:
A. Agent-
An animate or inanimate factor which must be present or lacking for
a disease or condition to occur.

Agent Factors-

Disease agent may be classified into following groups.
1. Biological agent- these are living agents of diseases, virus, fungi, bacteria, protozoa. These agents exhibit certain properties such as infectivity, pathogenicity, and virulence.

2. Nutrient agent- These can be proteins, fats, carbohydrates, vitamins, minerals and water. PEM, anaemia, goiter, obesity, and vitamin deficiencies are some of the nutritional problems.

3. Physical agent- exposure to excessive heat, cold, humidity, pressure, radiation, electricity, sound, etc. may result in illness.
4. Chemical agent-
Endogenous- some of the chemicals may produced in the body as a result of derangement in the body functions. E.g. urea (uraemia), serum bilirubin (jaundice), uric acid (gout), Calcium carbonate (kidney stone).

Exogenous- agents arising outside of human host e.g. fumes, dust, gases, insecticides etc. these may be acquired by inhalation, ingestion or inoculation.

5. Mechanical agent- exposure to chronic friction and other mechanical forces may result in crushing, tearing, dislocations and even death.

6. Social agents- these are poverty, smoking, unhealthy life styles, social isolation, maternal deprivation etc.
B. Host-
Living species, humans or animals capable of being infected or affected by an agent.
Host Factors –
The host factors may be classified as:

1. Demographic characteristics such as age, sex, race, etc.

2. Biological e.g. genetic factors.

3. Social and economic characteristics, education, occupation.

4. Life style factors, habits, nutrition, physical exercises, use of alcohol, drugs and smoking etc.

C. Environment –
Environment is a term used to describe all living and non-living things which surrounds man.
C. Environmental Factors-

Environment has been classified as three components

1. Physical environment

2. Biological environment

3. Psycho-social Environment