Identifying Outbreaks

Outbreaks generally come to the attention of state or local health departments in one of two ways:

  1. Astute individuals (citizens, physicians, nurses, laboratory workers) will sometimes notice cases of disease occurring close together with respect to time and/or location or they will notice several individuals with unusual features of disease and report them to health authorities.
  2. Public health surveillance systems collect data on 'reportable diseases'. Requirements for reporting infectious diseases in Massachusetts are described in 105 CMR 300.000 (Reportable Diseases, Surveillance, and Isolation and Quarantine Requirements). The Massachusetts Virtual Epidemiologic Network (MAVEN) is a new web-based disease surveillance and case management system that enables MDPH and local health departments to capture and transfer appropriate public health, laboratory, and clinical data efficiently and securely over the Internet in real-time. In addition, disease registries, such as the Massachusetts Cancer Registry, are also important components of the public health surveillance system.

For more information, see the online learning module on Surveillance.

Why Investigate Outbreaks?

The primary reason for conducting outbreak investigations is to identify the source in order to establish control and to institute measures that will prevent future episodes of disease. They are also sometimes undertaken to train new personnel or to learn more about the disease and its mechanisms for transmission. Whether an outbreak investigation will be conducted may also be influenced by the severity of the disease, the potential for spread, the availability of resources, and sometimes by political considerations or the level of concern among the general public.

Steps in the Investigation of a Disease Outbreak

Most outbreak investigations involve the following steps:

  1. Preparation for the investigation
  2. Verifying the diagnosis and establishing the existence of an outbreak
  3. Establishing a case definition and finding cases
  4. Conducting descriptive epidemiology to determine the personal characteristics of the cases, changes in disease frequency over time, and differences in disease frequency based on location.
  5. Developing hypotheses about the cause or source
  6. Evaluating the hypotheses & refining the hypotheses and conducting additional studies if necessary
  7. Implementing control and prevention measures
  8. Communicating the findings

Some of the steps may be conducted simultaneously, and the order may vary depending on the circumstances. For example, if new cases are continuing to occur and there are steps that can be taken to control the outbreak and prevent more cases, then certainly control and prevention measures would take top priority.