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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.

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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.

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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 features:

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  • • Continuous data collection and evaluation
  • • An identified target population
  • • A standard definition of the outcome under study
  • • Timely collection and dissemination of information
  • • Application of the data to disease control and prevention

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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 problems.

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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:

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  • • Identifying patterns of disease occurrence
  • • Detecting disease outbreaks or epidemics
  • • Developing ideas about possible causes
  • • Identifying cases for further investigation
  • • Planning health services to fulfill specific needs

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The term population-based means that the target group under study or surveillance is the general population, usually in terms of geographic residence.

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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.

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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 ...

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