How to Stop an Outbreak

How the scale and state of a disease informs the response

medical research in lab
Victor Torres/Stocksy United

In an age of when we are faced with news about a Zika outbreak, an Ebola epidemic, or an HIV pandemic, we sometimes get confused as to how large or pervasive these diseases might be.

While some people might consider the terms "outbreak," "epidemic," and "pandemic" interchange, other might uses them euphemistically (“bullying has become epidemic in schools”) or simply incorrectly.

From the point of view of an epidemiologist, the terms are specific in how they signify the scale and severity of disease when large numbers of people are involved.

Definition of Outbreak, Epidemic, and Pandemic

According to the Centers for Disease Control and Prevention (CDC), an outbreak is the occurrence of more cases of a disease than would normally be expected in a specific place or group of people over a given period of time. Outbreaks can range from food poisoning to enterovirus to seasonal flu.

The term epidemic essentially means the same thing but tends to connote a more serious occurrence. While an outbreak might suggest something that is geographically limited or constrained, an epidemic infers a crisis situation that can spread. It’s a subtle difference but an important one.

By contrast, a pandemic is an epidemic that is widespread and often global, usually affecting a very large number of people. While the term is suggestive of something more serious than an epidemic, it is only so by scale and not by the severity of the disease.

Another term used in epidemiological investigations is cluster.

This refers to a group of cases in a specific time and place that may or may not be greater than normal. Investigations of disease clusters are used to determine the normal or expected rate of a specific disease.

Meanwhile, a disease that maintains in an elevated but steady state within a population is said to be endemic.

For example, while an outbreak of HIV can occur in a specific area due to conditions that caused a sharp increase (as happened in Indiana in 2015 among injecting drug users), HIV can be considered endemic to another region where the rate of infection remains steady.

As such, epidemic refers to the scale of a disease above normal while endemic refers to the steady state of a disease that neither dies out nor changes considerably in the number of people affected.

The Goals of an Outbreak Investigation

Investigations of outbreaks are necessary to understand and ultimately control and prevent the spread of disease. By understanding how certain diseases are transmitted and analyzing their trend of infection, epidemiologist can pinpoint the source and find strategies to stop the disease.

Investigations are especially vital when a disease is severe and easily spread. The research of can help facilitate the development of new vaccines and drugs, implement public health policies, implement quarantines, and find ways to change behaviors known to increase transmission risk.

How a CDC Investigation Is Conducted

The CDC has issued a list of 10 steps used by epidemiologists to investigate outbreaks. The guidelines aim to ensure the rapid and accurate evaluation of an outbreak in order to contain the disease as quickly as possible and prevent harm to the public at large.

The steps are as follows:

  1. Prepare for field work. Investigators should be familiar with the disease (or suspected disease) and have a coordinated plan of action.
  2. Establish the existence of an outbreak. This includes examining health department surveillance reports, hospital records, and disease registries or conducting field interviews.
  3. Verify the diagnosis. Investigators will need to review the clinical findings and conduct lab tests to verify the diagnosis or determine the specific nature of the disease, if unknown.
  4. Define and identify cases. This starts with establishing what constitutes a case. By doing so, investigators can eliminate false-positives when counting the actual number of cases in a population.
  1. Describe the data in terms of time, place, and person. This include breaking down when each infection occurred, where it occurred, and kinds of people affected (by age, race, sex, etc.)
  2. Develop a hypothesis. This is a simply educated guess based on the data compiled.
  3. Evaluate the hypothesis. This requires crunching numbers to either support or not support the hypothesis.
  4. Refine the hypothesis and carry out additional studies. Additional studies may include lab tests or environmental studies.
  5. Implement control and prevention measures. These are the actions used to contain and prevent further spread of infection from the source.
  6. Communicate findings. Communications are meant to coordinate a public health response and to ensure the measures needed to end the outbreak are fully implemented.

Source:

Centers for Disease Control and Prevention (CDC). "Steps of an Outbreak Investigation." Principles of Epidemiology in Public Health Practice, 3rd ed. Atlanta, Georgia; updated September 15, 2016.

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