Epidemiology is the study of frequency, distribution and determinants of health related states and events including diseases and the application of this study to control the disease and other health problems. It can be also described as a branch of evidence based medical science that deals with the incidence, distribution and control of diseases in a population chiefly by use of statistics. In other terms, it is a sum of the factors controlling the presence or absence of a disease or a pathogen. Epidemiology is the basic science of and most fundamental practices of public health and preventive medicine. It studies the spread of diseases and measures to control it. It focuses on groups rather than individuals and often takes a historical perspective and retrospective in nature.
Epidemiology was first applied to the control of communicable diseases and public health through quarantine and isolation, even though ideas about disease transmission and microbiology and epidemiology were rudimentary. Epidemiology has evolved rapidly and in modern epidemiology, the attention has expanded from infectious and dietary diseases to identifying risk factors of chronic diseases, evaluation treatment modalities and thus provision of new opportunities for prevention, treatment, planning and improving the effectiveness and efficiency of health services. It has helped develop methodology used in clinical research, public health studies and to a lesser extent, basic research in biological sciences.
Determinants include both causes and factors that influence the risk of disease. Diseases may have single cause or multiple causes. In case of multiple factors, they can be divided into two groups:
Host factors that determine the susceptibility of the individual such as age, sex, race, genetic makeup, nutritional state, immunity etc.
Environmental factors that determine the host’s exposure to the specific agent such as overcrowding, hygienic