Introduction to Epidemiology

Concept of epidemiology

Epidemiology is the study of the occurrence. distribution, and determinants of health problems and diseases in human populations or communities and use of this knowledge for the prevention, control and treatment of diseases. The primary unit of study in epidemiology is a group of a person, not any single person. The population can be defined in geographical terms or a specific group of hospital patients or factory workers. The population used in epidemiology is that in a given area or country at a given time.

The word "Epidemiology" is derived from the Greek word epidemic.

Epi: on, upon, to

Demos: people

Logos: knowledge, doctrine, discourse, science

Thus, epidemiology in its broadest sense is the study of effects of multiple factors on human health. The applied science epidemiology requires divergent skilled persons in the team to do research and understanding the epidemiological principles of the disease or health problems. It is amultidisciplinary subject involving those of physicians, biologist, public health experts, infectious disease experts, dentist, veterinarian, public health nurses, sanitation discipline experts, nutritionist, health educator, social worker, statistician, sociologist, anthropologist, biochemist, meteorologist and others to work in team.

History of Epidemiology

The history of epidemiology goes back to Hippocrates (400 B.C.) thorughJohn Graunt (1662), William Farr, John Snow (both mid 80's) and others. The discipline did not blossom until the end of the Second World War.

Hippocrates (400 B.C.) attempted to explain disease occurrence from a rational instead of supernatural viewpoint. In his essay, entitled "On Airs, Waters and Place," Hippocrates suggested that environmental and host factors such as behaviours might influence the development of disease.

Another early contributor to epidemiology was John Graunt, who published his landmark analysis of mortality data in 1962. He was the first to quantify pattern of birth, death and disease occurence, noting male, female disparities, high infant mortality, urban rural differences and seasonal variations. No one built upon Graunt's qork until the mid 1800s, when william Farr begin systematicallt collect and analyze Britian's mortality statistics. Farr considered the father of modern vital statistics and disease classifications. He extends the epidemiologic analysisl of morbidity and mortility data, looking at the effect of marital status, occupation and attitude. He also developed many epidemilogic concepts and techniques still in use today.

Meanwhile, an anesthesiologist named John Snow was conducting the series of investigations in London that later earned him the title "father of field epidemiology'. Twenty years before the development of the microscope, Snow conducted studies of cholera outbreak both to discover the cause of disease and to prevent its recurrence. His work classicallly illustrate the sequence from descriptive epidemiology to hypothesis generation, hypothesis testing (analytic epidemiologic) and their application.

Snow conducted his classic study in 1854 when an epidemic of cholera developed in the Golden Square of London. he began his investigation by determining where in this area person with cholera lived and worked. he then used this information to map the distribution of cases.

Snow believed that water was the source of infection for cholera. He marked the location of water pump on his spot map and then looked for a relationship between the distribution of cholera infected households and the location of pumps. The studies added support to Snow's hypothesis, and demonstrated the sequence of step use today to investigate theoutbreak of disease. Based on acharacterization of the cases and population at risk by time, place and person, Snow developed a testable hypothesis. He then tested this hypothesis with a more rigorously designed study, ensuring that the groups to be compared were comparable. Thus with no knowledge of the existence of microorganisms, Snow demonstrated through epidemiologic studies that water could serve as a vehicle for transmitting cholera and that epidemiologic information could be used to direct prompt and appropriate public health action.

In the mid and late 1800s, many other in Europe and the United States began to apply epidemiologic methods to investigate disease occurrence. At that time, most investigation focused acute infectious diseases. In the 1900s, epidemiologist extended their methods to noninfectious disease. The period since the Second World War has seen an explosion in the development of research methods and the theoretical underpinning of epidemiology, and in the application of epidemiology to the entire range of health-related outcomes, behaviours and even knowledge and attitudes. The studies by Doll and Hill linking smoking to lung cancer and the study of cardiovascular disease among resisdents of Framingham, Massachusets are two examples of how pioneering researchers have applied epidemiologic methods of chronic disease since World War II, during the 1960s and early 1970s health worker applied epidemiologic methods to eradicate smallpox worldwide. This was an achievement in applied epidemiology of unprecedented proportions.

Today public health workers throughout the world accept and use epidemiology routinely. Epidemiology is often practiceand use by non-epidemiology routinely to characterize the health of their communitites and to solve day to day problems. This landmark in the evaluation of the disciplines is less dramatic than the eradication of smallpox, but it is no less important in improving the health of people everywhere.

Definitions of Epidemiology

Historical definitions

This definition exclusively states epidemiology as epidemics of diseases. New standard Dictionary of English language has historically defined epidemiology as the science or doctorine of epidemics.

With time the definition of epidemiology was extended from studies of epidemic to a consideration of the endemic phase of epidemic disease. Stedman's Practical Medical Dictionary mentioned epidemiology as the science of epidemics and endemic disease.

Consequently, the definition of epidemiology expanded from epidemic (cholera, plague, tuberculosis, malaria, etc) diseases to diseases not strongly characterized by epidemics (leprosy, rheumatic fever, foodborne diseases and other non-communicable diseases, etc). These areas of epidemiology are covered by the following two statements:

1. The science of infective diseases, their prime causes, propagation and prevention (Stallybrass, 1931).
2. The society of the mass phenomena of infectious diseases or the natural history of infectious diseases (Frost, 1927).

Later, the mass phenomena and natural history of any disease or physiological state was included in epidemiological concept (e.g. cancer. arteriosclerosis, hypertension etc.).

1. The study of disease, any disease, as a mass phenomena (Greenwood, 1935)
2. The study of condition known or reasonably supposed to influence the prevalence of disease (Lumsden, 1936).
3. With the emergence of more health concerns and circumstances important to human health and welfare, the concept of epidemiology was broadened. The important areas included were accidents, disaster, suicides, poisoning, medical care, injury, and other technical and administrative problems, etc.

Therefore, historical definitions of epidemiology can be summarized as the field of medical science which is concerned with the relationships of the various factors and conditions which determine the frequencies and distribution of an infectious process, a disease, or a physiologic state in a human community.

Modern definitions

Epidemiology is the science which concerns itself with the natural history of disease as it is expressed in groups of person related by some common factors of age, gender, race, ethnic group, location, occupation, and education as distinct from the development of disease in the individual.

Center for Disease Control, US Public Health Services has defined epidemiology as the study of the patterns of disease and the factors that cause disease in man.

Epidemiology is the study of the distribution and determinants of disease frequency in man. the first area describes the distribution or pattern of health status in terms of age, gender, race, geography, etc. The second area involves the explanation of the risks or casual factors of disease or health problems.

The widely accepted definition of epidemiology is "The study of the distribution and determinants of health-related states or events in specific populations and the application of this study to control of health problems".

Aims of Epidemiology

According to the International Epidemiological Association (IEA), epidemiology has three main aims:

1. To describe and analyze disease occurrence and distribution in human populations;
2. To identify aetiological factors (risk factors) in the pathogenesis of disease; and
3. To provide the data essential to the planning, implementation and evaluation of services for the prevention, control and treatment of diseases and to the setting up of priorities among those services.

References

Atlas, RM and R Bartha. Microbial Ecology:Fundamentals and Applications. The Benjamin Cummins Publication co. Inc., 1998.

Gordis, L. Epidemiology. third edition. 2004.

Maier, RM, IL Pepper, and CP Gerba. Environmental Microbiology. Academic press Elsevier Publication, 2006.

park, K. Park's Text Book of social and prevention Medicine. 18th edition. 2008.