One of the initial reasons for developing epidemiological concepts
and methods was to study the natural history of disease. With knowledge
about the cause(s) of a disease or health problem, a solution could
be derived, along with preventive measures for the future. The two
primary intents were to identify, describe, and understand infectious
disease epidemics that could kill a large part of a population and
to maintain health surveillance of a population so that new diseases
and problems could be recognized.
Surveillance continues to be a very important aspect of public
health. It is the central function of pharmacoepidemiology, as noted,
for instance, in the postmarketing surveillance of pharmaceutical
products. The goal of this activity is identification of adverse
reactions, side effects, and even new beneficial effects of medications
used by a population.
One of the most basic functions of epidemiology is detecting
the occurrence of health problems or exposures in a target population.
This process of detection, called medical surveillance, is conducted to identify
changes in the distribution of diseases, thereby permitting their
prevention or control within the population. The term surveillance means “to watch
over.” Medical surveillance traditionally involved monitoring
the spread of infectious diseases through a population. Today, however,
surveillance programs are applied to a variety of health problems
and conditions. Medical surveillance involves the following key
- • Continuous data collection
- • An identified target population
- • A standard definition of the outcome
- • Timely collection and dissemination
- • Application of the data to disease
control and prevention
Surveillance activities provide data about the distribution of
a disease by person, place, and time. These three classic variables
are the most important in epidemiology, because patterns of occurrence
indicated by these variables can help identify possible causes of
a disease. A great variety of information is collected during surveillance,
including demographic information about affected and unaffected
individuals, their behaviors, and the geographic location of health
Many diseases, such as cancer, heart conditions, sexually transmitted
diseases, and drug addiction, are studied through medical surveillance.
The goals of medical surveillance activities include the following:
- • Identifying patterns of disease
- • Detecting disease outbreaks or
- • Developing ideas about possible
- • Identifying cases for further investigation
- • Planning health services to fulfill
The term population-based means
that the target group under study or surveillance is the general
population, usually in terms of geographic residence.
The key aspect of medical surveillance, and epidemiology as a
method, is the notion of counting. Numerical results compiled in
various formats represent the information available to epidemiologists
for deriving answers to research questions.
Some of the terms used to represent numerical findings in epidemiology
can be confusing. Good examples of often-misused terms include ratio,
proportion, percentage, and rate. In general, a ...