10.2A: Occurrence of a Disease
- Recognize the steps taken by epidemiologists when investigating disease outbreaks
Outbreak is a term used in epidemiology to describe an occurrence of disease greater than would otherwise be expected at a particular time and place. It may affect a small and localized group or impact 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 endemics that affect a particular place or group, epidemics that affect a region in a country or a group of countries, and pandemics that describe global disease outbreaks.
The epidemiology profession has developed a number of widely accepted steps when investigating disease outbreaks. 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 (if the group of ill persons is 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.
- Develop a hypothesis (if there appears to be a cause for 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.
There are several outbreak patterns that can be useful in identifying the transmission method or source and predicting the future rate of infection.
- 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.
Each has a distinctive epidemic curve, or histogram of case infections and deaths.
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.
Key Points
- Outbreaks may also refer to endemics that affect a particular place or group, epidemics that affect a region in a country or a group of countries, or pandemics that describe global disease outbreaks.
- The epidemiology profession has developed a number of widely accepted steps to investigate a disease occurrence.
- Outbreak patterns, which can be useful in identifying the transmission method or source, and predicting the future rate of infection include common source, continuous source, point source, and propagated source.
- Outbreaks can be behavioral risk related (e.g., sexually transmitted diseases, increased risk due to malnutrition) or zoonotic (e.g. the infectious agent is endemic to an animal population ).
Key Terms
- outbreak : A term used in epidemiology to describe an occurrence of disease greater than would otherwise be expected at a particular time and place.
- epidemic : A widespread disease that affects many individuals in a population.
- pandemic : A disease that hits a wide geographical area and affects a large proportion of the population.