WHO does not limit its definition of health to the mere absence of disease or disability. Health is a state of complete physical, mental and social well–being.
Advances in biology in the last two centuries gave currency to the germ theory of causation of disease. However, the emergence of so called modern disease of civilization, such as cancer, coronary heart disease, mental illness etc. as major public health problems, and even more importantly our inability to reduce the incidence of medically curable diseases like TB and leprosy, led to more holistic understanding of disease causation, and understanding that in includes social, economic, psychological and genetic causes as well as more immediate causes.
For instance, not everyone exposed to the tubercle bacilli develops tuberculosis, it has been found that factors such as poverty, over–crowding and malnutrition contribute significantly to its spread. Similarly, it is a malnourished child who is much more likely to succumb to measles, and it is a rural child without access to clean potable water who is more likely to die of diarrhea.
Therefore, to interpret a death due to TB, measles or diarrhea exclusively in terms of bacilli is at best to focus primarily on the most proximate cause of mortality. Much more fundamentally, these deaths are caused by poverty and its associated deprivations of sanitation, drinking water, nutrition, health education, health services and so on.
The significance of this is that it is erroneous and futile to expect the conquest of disease and promotion of health primarily through curative interventions by health professionals. The deaths we spoke of above and the tragic range of disease, disability, epidemics and mortality that the poor are routinely subjected to, could be prevented effectively by interventions such as livelihood promotion for the rural and urban poor, increased productivity in dry land farming, an employment guarantee program with a food for work component, sanitation, drinking water, improved shelter programs and effective implementation of PDS and ICDS. To acknowledge the social basis of disease is to recognize that range of equity–based state and social interventions would have direct, even critical bearing on public health.