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How do epidemiologists identify and investigate outbreaks

How do epidemiologists identify and investigate outbreaks? This article describes how scientists build evidence about outbreaks.
© UNSW Sydney
In this article, you will learn about different types of outbreaks, common outbreak patterns and we will look briefly at how epidemiologists identify and investigate outbreaks.
Epidemiologists and public health physicians talk about three types of outbreaks.  The first type is a common source outbreak. Common source outbreaks are outbreaks that start when a contaminant or infectious organism is distributed from a single source to a group of people. This distribution could be natural, caused by humans unintentionally, or intentionally caused by humans (bioterrorism). When the common source outbreak is due to illness in a group of people that had direct exposure to the same source of contamination in a short period of time, then it’s called a point source outbreak. If the source of exposure continues or occurs again and again after intervals of time, then you can have a continuous or intermittent common source outbreak.
Propagated outbreaks are when the infectious agent can be transmitted from one person to another. The original source might be a point source, but the outbreak can grow into an epidemic because the original infection passes from one person to another.
Outbreaks can start in many different ways. A person can be exposed to a food-borne pathogen through eating in a restaurant or a food they purchased at the supermarket for example. A mosquito-borne infection can enter mosquito populations and then be transmitted to humans when the moquitoes bite them. The speed at which a disease moves through a group of people depends on a number of factors. These factors might include, how quickly the infectious organism causes symptoms following the infectious exposure, what stage transmission to others occurs, the nature of the exposure event that causes transmission, as well as how immune to the infection individual people are. All of these factors can lead to very different patterns.
Outbreaks are identified through public health surveillance and there are local, regional, national and international systems in which outbreaks are monitored and managed. Generally, public health surveillance is the continuous, systematic collection, analysis and interpretation of health-related data needed for the planning, implementation, and evaluation of public health practice. There are surveillance systems operated by health departments and international organisations for identifying outbreaks. Outbreaks can be identified by alert members of the public, doctors who see unusual patterns of patients as well as through organised surveillance systems that rely on information being continuously reported, collected and analysed to identify unusual occurrence of illness.
The first step in an outbreak investigation is to confirm the outbreak. This usually involves talking to the doctors who diagnosed the disease and the patients, and looking for common features between each person that might suggest a connection. The next step is to confirm the diagnosis which often requires laboratory confirmation of the infection.
Other steps involve defining what it means to be a case in the outbreak (the case definition), identifying other cases, gathering data, analysing the data. Deciding on control measures for the outbreak is another aspect. Sometimes a scientific epidemiological study is conducted to obtain statistical evidence of the causes of the outbreak. The outbreak investigation would usually be managed by local health officials that might include public health physicians or epidemiologists. Larger outbreaks might need to be managed at state, national or even international level. Communication between officials and the public is an important aspect of outbreak investigations.
After reading this article, discuss the answers to the following questions in the comments section below:
Can you find three other examples of point source outbreaks? Can you find three examples of propagated outbreaks? Why do you think these are each a type of outbreak?
Ask yourself these questions:
  • When and where did the outbreak start?
  • How did they know these things?
  • What would have been the earliest signs that an outbreak was occurring?
© UNSW Sydney
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Biosecurity and Bioterrorism: Public Health Dimensions

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