Step 2: Define and Find Cases

Finding sick people is important to help public health officials understand the size and severity of a possible multistate outbreak and decide if there is ongoing risk to the public. Outbreak investigators develop a case definition to define which sick people will be included in the outbreak. They also use this definition to search for additional sick people that are part of the outbreak.

Case definitions

Case definitions define who will be included as part of the multistate outbreak. Multistate outbreak case definitions usually include details about:

  • The bacteria causing the illness
  • DNA fingerprint of the bacteria
  • When the illnesses occurred
  • Symptoms of the illness

Multistate outbreak case definitions do not typically limit who is included in the outbreak based on what state the sick person lives in or demographic characteristics of the sick person, such as age, gender, or race.

The number of sick people that meet the case definition is called the case count.

Finding cases of illness

Using the case definition, local, state, and federal investigators search for more cases related to the outbreak. For multistate outbreaks, investigators review DNA fingerprint information on cases reported through PulseNet.

State and local officials may also look at other information to find cases that may be part of the outbreak and work to get DNA fingerprinting information, including:

  • Reviewing regular surveillance reports
  • Asking local clinical and laboratory professionals to report cases more quickly, as soon as they suspect the diagnosis
  • Reviewing emergency room records for similar cases
  • Surveying groups that may have been exposed at restaurants or events
  • Asking public health officials in surrounding areas to look for cases that might be related