Disease outbreak

In epidemiology, an outbreak is a sudden increase in occurrences of a disease when cases are in excess of normal expectancy for the location or season. It may affect a small and localized group or impact upon thousands of people across an entire continent. The number of cases varies according to the disease-causing agent, and the size and type of previous and existing exposure to the agent. Outbreaks include many epidemics, which is a term normally only used for infectious diseases, as well as diseases with an environmental origin, such as a water or foodborne disease. They may affect a region in a country or a group of countries. Pandemics are near-global disease outbreaks when multiple and various countries around the Earth are soon infected.

Definition

The terms "outbreak" and "epidemic" have often been used interchangeably. Researchers Manfred S. Green and colleagues propose that the latter term be restricted to larger events, pointing out that Chambers Concise Dictionary and Stedman's Medical Dictionary acknowledge this distinction.

Outbreak investigation

When investigating disease outbreaks, the epidemiology profession has developed a number of widely accepted steps. As described by the United States Centers for Disease Control and Prevention, these include the following:

Identify the existence of the outbreak (Is the group of ill persons normal for the time of year, geographic area, etc.?)

Verify the diagnosis related to the outbreak

Create a case definition to define who/what is included as a case

Map the spread of the outbreak using Information technology as diagnosis is reported to insurance

Develop a hypothesis (What appears to be causing the outbreak?)

Study hypotheses (collect data and perform analysis)

Refine hypothesis and carry out further study

Develop and implement control and prevention systems

Release findings to greater communities

The order of the above steps and relative amount of effort and resources used in each varies from outbreak to outbreak.