Outbreak

For other uses, see Outbreak (disambiguation).

In epidemiology, an outbreak is a sudden increase in occurrences of a disease in a particular time and place. It may affect a small and localized group or impact upon thousands of people across an entire continent. Two linked cases of a rare infectious disease may be sufficient to constitute an outbreak. Outbreaks may also refer to epidemics, which affect a region in a country or a group of countries, or pandemics, which describe global disease outbreaks.

Outbreak investigation

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

• Verify the diagnosis related to the outbreak
• Identify the existence of the outbreak (Is the group of ill persons normal for the time of year, geographic area, etc.?)
• 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 hypothesis (collect data and perform analysis)
• Refine hypothesis and carry out further study
• Develop and implement control and prevention systems
• Release findings to greater communities

Outbreak debriefing and review has also been recognized as an additional final step and iterative process by the Public Health Agency of Canada.

Types

There are several outbreak patterns, which can be useful in identifying the transmission method or source, and predicting the future rate of infection. Each has a distinctive epidemic curve, or histogram of case infections and deaths.

• Common source – All victims acquire the infection from the same source (e.g. a contaminated water supply).
  • Continuous source – Common source outbreak where the exposure occurs over multiple incubation periods
  • Point source – Common source outbreak where the exposure occurs in less than one incubation period
• Propagated – Transmission occurs from person to person.

Outbreaks can also be:

• Behavioral risk related (e.g., sexually transmitted diseases, increased risk due to malnutrition)

• Zoonotic – The infectious agent is endemic to an animal population.

Patterns of occurrence are:

• Endemic – a communicable disease, such as influenza, measles, mumps, pneumonia, colds, smallpox, which is characteristic of a particular place, or among a particular group, or area of interest or activity.

• Epidemic – when this disease is found to infect a significantly larger number of people at the same time than is common at that time, and among that population, and may spread through one or several communities.

• Pandemic – occurs when an epidemic spreads worldwide.

Outbreak legislation

Outbreak legislation is still in its infancy and not many countries have had a direct and complete set of the provisions. However, some countries do manage the outbreaks using relevant acts, such as public health law.

See also

• 1993 Four Corners hantavirus outbreak
• 2003 Midwest monkeypox outbreak
• 2007 Yap Islands zika virus outbreak
• Super-spreader
• 1947 New York City smallpox outbreak
• 2014 Democratic Republic of the Congo Ebola virus outbreak