What is Epidemiology?


• the study of the distribution and determinants of diseases or other health outcomes in populations


Diseases and other health outcomes

• Infectious process – influenza, cholera, smallpox, malaria, HIV, tuberculosis, etc.

• Non-infectious diseases – cancer, diabetes, coronary heart disease, malnutrition, schizophrenia, etc.

• Other health outcomes (non-disease) – homicide, motor vehicle accidents, shark bites, etc.

Other terms used to classify disease

• Acute (short-term) versus (vs.) chronic disease

• Gradual vs. sudden onset

• Contagious vs. non-contagious

• Curable vs. incurable

• Treatable vs. untreatable

• Fatal vs. non-fatal


Key Concepts

• Case definition

standard set of criteria for determining whether a person has the disease or health outcome of interest


Construction of a case definition

Can include:

– Physical signs

– Symptoms

– Results of laboratory tests

• Usually time-bounded as to occurrence


Distribution of disease

the frequency of occurrences of disease or health outcome, as well as the definition of which individuals are experiencing the disease


Characteristics used to define distribution of disease

• Person – who in terms of age, gender, ethnicity, occupation

• Place – where in terms of geography – country, region, neighborhood, proximity to a specific feature

• Time – when in terms of year, season, or relative to an event


Key Concepts

• Numerator

– the number of cases identified which meet the case definition criteria

• Denominator

– the number of persons in the population that is the source of the cases


Determinants of disease and their use

– Factors that influence the occurrence of disease or other health outcomes

– To explore the why and how of disease distribution


How did epidemiology begin?

• Observation and inquiry

• Identifying patterns rather than randomness

– Hippocrates (5th century BC) “On airs, waters and places”


Modern epidemiology

• John Graunt (1660s)

– “ … Bills of Mortality”

• William Farr (1840s)

– “Reports of the Registrar General”

• John Snow (1850s)

– “On the mode of communication of Cholera”




Objectives of Epidemiology

• Identify etiology of disease

• Determine the burden of disease

• Study the natural history of disease

• Evaluate health systems

• Provide foundation for public policy


Why Epidemiology?

Expand knowledge of disease and other health-related events in order to provide:

– Primary prevention of new cases of disease

– Secondary and tertiary prevention

– mitigate the consequences of existing health problems

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