Epidemiology is an old world, dating back to the third century BC and has its origin in the idea first expressed over 2000 years ago by Hippocrates and others, that environmental factors can influence the occurrence of disease. The word ‘epidemiology’ is derived from the Greek word, ‘Epidemic’. ‘Epi = upon’, ‘demos = people’, ‘Logos = science’. The branch of medical science which deals with the treatment of epidemics”. Epidemiology as “the study of the distribution and determinants of health related states or events in specified populations, and the application of this study to the control of health problems”.