Epidemiology of Infectious Diseases includes a wide range of topics including studies on various epidemic diseases using methods like supervision, monitoring, statistical inference, analytic researches and experiments. Epidemiology is the occurrence of communicable and chronic diseases, principally in the form of epidemics which is caused by microbial infection. Infection is the invasion of foreign microbial organism on our immune system for its survival and growth. Etiology is the study of cause or origin. In epidemiology etiology plays a vital role to understand the origin and cause of the disease. By studying the etiological conditions of infectious diseases, communicable and non-communicable diseases its cure and prevention can be intervened. Emerging infection is the infectious disease that has increased rapidly compared to the past condition and tends to increase in the future. Emerging infectious diseases range 12% of all the total deadly pathogens which can cause fatal effects. Primary care epidemiology can contribute to wider improvements in health and healthcare services, through better understanding of disease aetiology, use of healthcare services and the role of different healthcare interventions. Primary care is delivered by a wide range of health professionals, nurses, doctors, care assistants, mental health specialists, dieticians, pharmacists, dentists, optometrists and other health care professionals.