When you visit a physician with some complaint, he examines sign and symptoms and takes help of laboratory test to reach diagnosis. He writes the prescription from his knowledge about medicine and prescribes only those medicines that have been recommended by the scientists and approved by medical science authorities. In other words, diagnosis is the major skill of a physician while the scientists investigate causes of diseases and their cure. Scientists study human diseases using the following three approaches, which are complementary to each other.
1) The basic science approach
2) The clinical approach
3) The epidemiological approach
In the basic science approach, the cause of the disease — physical, chemical, biological or any other is investigated in detail. The clinical approach involves the study of sick people and the physiological symptoms due to disease and the conditions that will arrest or relieve the symptoms.
The epidemiological approach examines the relative frequency of a disease within defined population or a fraction of it that may be large or small. Obviously, a group of people or community or larger population are exposed to a common environment, epidemiological approach is an important way of studying the influence of environmental contaminants on human beings. It encompasses two main areas:
a) Descriptive Epidemiology:
In which a study of the distribution of disease or health hazards in the human population is conducted.
b) Analytic Epidemiology:
In which a study of the determinants or underlying causes or risk factors of disease is undertaken.
The main objective of epidemiology is to understand or discover the cause of diseases and suggest best means of prevention of diseases or controlling their spread and provide guidance to Health Services.
In the epidemiological approach, the following five basic questions have to be answered.
1) When does the disease occur? (Time)
2) Where does the disease occur? (Place)
3) Who are the people affected? (Persons involved)
4) Why has it happened? (Causes)
5) What should be done to prevent or control the disease? (Prevention, control and eradication)
Such approach helps in identifying the environmental causative of the disease and suggests the ways of its prevention.
For example, in epidemiological study of respiratory disorders in an area, it was found that disease has been prevalent for some years, the affected people work in textile industry and show common symptoms of disease. Among the workers only those are affected who breathe in fibers. So fibers are linked with disease. After verification of such data, physical and medical means of control and prevention of disease can be planned.
Environmental factors are considered in the light of area of incidence and time of exposure. For example, a single event such as an accident in a chemical plant requires immediate instant study of factors different from a long-term hazard due to coal and zinc mining.