Concept of health and disease | Epidemeology

Concept of health and disease | Epidemeology

Concept of health 

In an ancient period explain as an absence of disease another said “A condition of body free from physical diseases”. A condition of the soundness of any organism that stays in which all the natural functions are performed freely without pain. Some people said that help is free from sickness. 

In 1984, WHO gave a widely accepted and recognized definition that is health is a complete state of physical, mental and social well-being not merely an absence of disease or infirmity. 

Concept of disease 

In an ancient period, the term disease was defined in many ways i.e. 

  • The departure of the body parts. 
  • Impaired of body 
  • Dysfunction of body parts 
  • Interruption of performing of vital organs etc. 


Physiological and psychological dysfunction of the external and internal parts of the body which is identified by the various medical diagnostic test is called disease. 

Concept of disease causation 

In an ancient period, till the time of Louise Pasteur, Various concepts were in the practice of disease causation. Eg. Supernatural power, god created curse, devil eyes, tuna Muna, majestic theory, theory of humour etc. 

These all were the theory of rumours after the discovery of microbiology, the concept was changed. 

A. Germ theory of disease 

Louis Pasteur, the chemist changed the concept of disease causation. He demonstrated the presence of microorganisms in the air. He said that the disease is caused by various small microorganisms which we couldn’t see with our naked eyes and not caused by a supernatural power or by miasma. In 1877, Robert Koch showed that anthrax was caused by bacteria.

The Germ theory of disease was confirmed by Pasteur and Koch. It was a golden age of bacteriology. 

Criticism has also appeared against germ theory. However, they couldn’t think beyond the germ theory of disease. it is now found that disease is rarely caused by a single agent but by multiple factors. 

B. Multi-factorial causation of disease 

Multi-factorial causation of means there is multiple factors in disease causation. it is an improved theory of germ theory. This theory was purpose by Pettenkofer of Munich.

This theory explains that disease is not only caused by a single agent like in germ theory but by many other factors. social, economic, cultural genetic and physiological factors are equally important for disease causation. For example: – Tuberculosis is not only caused by Tubercle bacilli, other factors such as poverty Overcrowding and malnutrition are also equally important for its occurrence.

This theory now is used to describe the diseases such as chronic heart disease, and cancers which are caused by multiple factors. Examples are excess fat intake, smoking, lack of physical exercise, obesity etc. 

Concept of health and disease | Epidemeology

C. Web causation of disease 

This model was first suggested by Make Mohan and Pugh. This model is used in the study of chronic disease where the disease agent is generally unknown, but the outcome is the interaction of multiple factors. 

In Web causation, there is not only one factor but several factors or conditions that help to cause a single disease which is known as risk factors or predisposing factors. 

The web causation was developed especially to enhance the understanding of chronic diseases such as cardiac vascular disease. However, it can also be applied to the study of injury and communicable disease. 

It is often difficult to find causes for health-related events or chronic diseases as they are multiple and heterogeneous. All these factors collectively form the “Web of causation” where every cause is interconnected. 

D. Iceberg phenomenon of disease 

It is closely related to the spectrum of diseases. The Iceberg phenomenon shows the disease pattern seen in a community.

Here in this phenomenon, the floating tip of the iceberg represents what the physician sees in the community i.e., the symptomatic phase of the disease and the hidden part of the ice represent what the physician cannot see that is pre-symptomatic.

The visible part of the iceberg denotes the clinically apparent cases of the disease in the community so this denotes that everyone can see the disease which shows the clinical symptoms. The part of the iceberg below the water level denotes the latent, subclinical, undiagnosed and carrier states in the community.

The main role of the health personnel is to identify the hidden part that is the pre-symptomatic phase of the disease and prevent them. 

E. Spectrum of disease 

A graphic representation of the variations in the manifestations of the disease is known as the “Spectrum of diseases”. We can compare this spectrum of disease to the spectrum of light from a prism where the colours vary from one end to the other but it is difficult to determine where the colour ends and the other begins.

Same wise, at the one end of the disease spectrum, are sub-clinical infections that are not ordinarily identified and at the other end are fatal illnesses.

In the middle of the spectrum lie illness ranging in severity from me to CBR, these manifestations depend upon the state of unity the study of a spectrum of diseases helps in the early diagnosis and treatment of disease by using a preventive measure that stops the further development of the disease. 

Leprosy is an excellent example of the spectrum concept of disease. 

Concept of health and disease | Epidemeology

F. Natural history of the disease 

The natural history of disease is the key concept of epidemiology. Natural history of one of the major elements of descriptive epidemiology. We study the natural history of disease from the earliest stages of its pre pathogenesis phase to its termination as recovery disability or death.

Each disease has its own unique natural history which is not the same for every individual. The natural history of established by Cohort study. For creating a natural history of the disease, it is necessary to make a framework to understand the Pre-pathogenesis and pathogenesis phases of a particular disease.

Pre-pathogenesis phase is the process in the environment phase is a process in the host. These two phases are the main core component of the natural history of the disease. 

1. Pre-pathogenesis phase 

We have already discussed earlier that it usually occurs in the environment. This phase is preliminary to the onset of disease in man. In this stage, the disease agent is not entered in man but many interactions with the human already occurred in the environment.

In this stage, man is exposed to the risk of disease. Actually, we all are in the Pre-pathogenesis phase of many communicable and non-communicable diseases. 

2. Pathogenesis phase 

The phase begins when the disease agent in the human host and the development of the disease agent occurs in the pathogenesis phase and creates the health problem. The final outcome of the disease may be recovery, disability or death. 

The study of the pathogenesis phase of is the natural history of the disease is important because it helps to know where and how the stage of the disease is going on so that we can organize the intervention program on time and prevent the further worsening of the disease and the health of the patient. 

G. Risk factors 

Risk factors are defined as the probability of developing a disease or experiencing a fluctuation in health status. Those factors that increase the probability of disease outcome are called “Risk factors”. Examples: – Genetic, environmental, social, behavioural etc.

The study of risk factors is not only applicable in non-communicable diseases but also in communicable diseases. Risk factors may be true, causative examples: – Smoking and lung cancer, merely contributory (e.g., lack of physical exercise and chronic heart disease) or only predictive (e.g., illiteracy and prenatal mortality).

Some risk factors are modifiable and others are non-modifiable. Risk factors are needed for the study of epidemiological methods like case-control studies and cohort studies. If the risk factors are reduced then the occurrence of disease will be reduced. 

Examples of risk factors  

Disease  Risk factors 
Heart Disease  Smoking, high serum cholesterol level, increased blood pressure, diabetes, obesity, lack of exercise 
Cancer Smoking, alcohol, radiation, drugs, environmental pollution, occupational hazard 
Stroke High blood pressure, smoking, alcoholism, high serum cholesterol  
Diabetes Obesity, high carbohydrate diet 
Cirrhosis of liver Alcoholism 

H. Risk group 

Those groups of people who are at increased risk of developing the disease are caused by “Risk groups”. Identification of risk groups helps to define priority and point to those who are in need of attention.

The risk approach is a managerial device for increasing the efficiency of health services within limited local resources. The knowledge of risk factors and risk groups can be used to prevent disease and hence be used to prevent disease and hence we are able to remove or minimize the risk. 

Guidelines for Defining Risk Group 

1. Biological situation 

  • Age: – infants, children, old age, adolescent 
  • Sex: -Male/female of reproductive age 
  • Physiological status: – pregnant women, High blood pressure etc. 
  • Genetic factors: – Family history. 

2. Physical situation 

  • Rural, urban living conditions 
  • Overcrowding, water supply 
  • Environmental etc. 

3. Socio-cultural situation 

  • Social class 
  • Ethic and cultural Group 
  • Family housing 
  • Customs 
  • Habits 
  • Behaviour 
  • Lifestyles etc. 
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