Investigate an Outbreak

Key points

  • Investigation into the clinical and epidemiologic features, as well as the etiology of outbreaks is particularly important to public health.
  • Investigate severe unexplained respiratory outbreaks to rule out emerging health threats.
Person typing on laptop

Outbreaks to investigate

For each respiratory disease outbreak, public health officials determine the appropriate level of public health response. They must consider many factors in making the decision, such as availability of resources and competing agency priorities. However, several characteristics of respiratory outbreaks typically warrant further investigation and an urgent response.

The characteristics below, while not comprehensive or definitive, can help determine which outbreaks merit further investigation:

  • Unknown etiology after initial work-up
  • Associated with severe disease manifestations (e.g., need for hospitalization, death)
  • May be useful to answer epidemiologic, laboratory, or infection control questions
  • Possible vaccine-preventable diseases
  • Associated with congregate settings or with a likely (controllable) environmental source
  • Respiratory infection potentially caused by a bioterrorism agent
  • Outbreaks that have generated excessive public anxiety
  • Either very large or rapidly progressing

Single case evaluation

In certain situations, public health officials may need to evaluate a single case of unexplained respiratory disease as a possible outbreak. Examples include diseases with the potential need for immediate public health intervention, such as:

  • Suspect pulmonary anthrax
  • Plague
  • Avian influenza
  • Middle East Respiratory Syndrome
  • Hantavirus pulmonary syndrome

Requesting assistance‎

View guidance on when and how to reach out to CDC for help investigating an unexplained respiratory disease outbreak.

Epidemiological investigation components

Below are some of the common components of an epidemiological outbreak investigation. The circumstances in any given outbreak may require additional steps.

Outbreak and case definitions

Developing a clear case definition is critical to effective investigation of an outbreak.

Collect information

Begin collecting available epidemiologic, clinical, and laboratory information to help assess the situation. See this respiratory outbreak survey for an example on the types of information you might want to gather.

The following tools will help guide the next steps:

Keep Reading: Create an Epi Curve

Develop public health response

The initial information gathered may lead to additional questions in order to gauge the degree of response.

The following steps may help inform an appropriate response:

  • Assess the need and potential for interventions
  • Consider the likelihood of natural versus intentional source of infection
  • Evaluate the level of public health, clinician, or community concern

Potential interventions can include:

  • Cohorting
  • Quarantine
  • Vaccination
  • Use of prophylaxis
  • Elimination of disease source

Report and respond

Coordinate the public health response by:

  • Notifying appropriate local or state public health officials
  • Notifying CDC, if indicated, of the outbreak by
    • E-mailing URDO (M-F; 8 am–4 pm EST) or
    • Calling the emergency, after-hours hotline at 770-488-7100.

Data collection forms

How to use these forms

Public health officials may wish to gather additional information about possible exposures using data collection forms. These forms can assist in the interview and investigation of single cases of disease. Adapt these forms to collect information relevant to identifying etiologies of respiratory outbreaks.

How not to use these forms

Don't use these forms to report a disease outbreak to CDC. For reporting assistance, please refer to your state health department.