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:[1]

  • 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.[2]


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.[3]

  • Common source – All victims acquire the infection from the same source (e.g. a contaminated water supply).[4]
    • 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[5]
  • Propagated – Transmission occurs from person to person.[6]

Outbreaks can also be:

  • 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.[8][9] However, some countries do manage the outbreaks using relevant acts, such as public health law.[10]

See also


  1. ^ Steps of an Outbreak Investigation, EXCITE | Epidemiology in the Classroom | Outbreak Steps
  2. ^ Public Health Agency of Canada. "Canada’s Food-borne Illness Outbreak Response Protocol (FIORP) 2010: To guide a multi-jurisdictional response". Retrieved 22 March 2013. 
  3. ^ [1][dead link]
  4. ^ Glossary of Epidemiology Terms, (2007-04-25). Retrieved on 2010-11-25.
  5. ^ Glossary of Epidemiology Terms. (2007-04-25). Retrieved on 2010-11-25.
  6. ^ Glossary of Epidemiology Terms. (2007-04-25). Retrieved on 2010-11-25.
  7. ^ [2][dead link]
  8. ^ "Bioterrorism Training and Curriculum Development Program". Retrieved 2 August 2008. 
  9. ^ Star Publications. "‘Outbreak actions protected by law’". Retrieved 2 August 2008. 
  10. ^ The State of Queensland Government. "Legislation and Powers of Entry". Retrieved 2 August 2008. 

External links