Outbreak Investigation

Outbreaks are generally considered over after two incubation periods have passed since the last onset date occurred. Once the outbreak is over, a final outbreak report should be completed to summarize the outbreak investigation. The type of final documentation depends on whether the outbreak was more routine or expanded.

Routine outbreak investigations are common outbreak investigations where the agent is known (or inferred based on epidemiological data) that often results in minimal public health intervention. In addition, these routine investigations rarely require the use of epidemiologic studies for hypothesis testing. Examples of routine outbreak investigations may include norovirus, influenza, or COVID-19 in long-term care facilities or school settings, scabies outbreaks in any type of institution, or hand, foot and mouth disease outbreaks in child care settings. There may be situations where these examples may require formal documentation such as any novel findings, a new strain of the agent, or other factors or findings that may further the body of knowledge about the agent. Final documentation for routine outbreaks should include a Missouri Outbreak Report Form (MORF) and an epidemic curve. The outbreak report should be completed and submitted to the District Epidemiologists within two weeks of the conclusion of the outbreak. Please contact the District Epidemiologists for assistance in the event circumstances arise that prevent completion of the report within the two-week timeframe.

Expanded outbreak investigations are outbreaks that require a more in-depth and multi-faceted investigation, and therefore necessitate a more thorough manner of documentation. Examples of expanded outbreaks include outbreaks where the primary mode of transmission may be through food or water, or when there is prolonged person-to-person spread. It is critical to document aspects of these outbreaks such as study design, statistical findings, environmental findings, laboratory results, and control measures. Final documentation for expanded outbreaks should include a MORF and a formal written report of the investigation with an epidemic curve.

Waterborne outbreaks require extensive data collection and, as such, the MORF cannot be substituted. For waterborne outbreaks the final documentation should include a NORS [Needs Link] Form and a formal written report of the investigation with an epidemic curve. The outbreak report should be completed within 90 days after the conclusion of the outbreak. Please contact the District Epidemiologists for assistance in the event circumstances arise that prevent completion of the report within the 90-day timeframe.

A formal outbreak report should contain the following components:

• Name of Investigation - Provide a name that is unique to the investigation. The investigation name should start with the Outbreak ID Number followed by any combination referencing the location (city, county, state, multi-state), group affected (venue, vicinity, etc.), time frame of outbreak (month, season, year, etc.), the name of the agent, or other variables applicable to the outbreak. o 22-CD-##: Salmonellosis Outbreak Among Campers in Wayne County, Summer 2022
  • 23-CD-##: Outbreak of Acute Gastroenteritis of Unknown Etiology Among Elementary Students in St. Louis County, April, 2023
  • 23-CD-##: Multi-County Outbreak of E. coli O157:H7 Outbreak Among Attendees of a Wedding, November, 2023.
• Lead Investigator(s) - Provide the name and affiliation of the individual leading/coordinating the investigation. Provide the names and/or affiliations of other co-investigators.
• Date - Provide the date of the final report; This will be the date the LPHA submits the report to the District Epidemiologists for review.
• Prepared By – List the name(s) and affiliation(s) of the author(s) of the report; this is the person(s) that should be addressed if questions about the report arise.
• Introduction - Provide descriptive information regarding who identified the outbreak and/or how it was reported; date of the initial report; and summarize the situation (initial number ill, initial symptoms, etc.).
• Background - Provide general background information regarding the location where the outbreak occurred; the epidemiologic description of the pathogen (if known), such as the reported incubation period, duration of illness, disease severity; any laboratory details and or surveillance data.
• Methods - Provide information on case finding, study design, how information was collected and applicable case definitions for the outbreak. Include methods on sample collection (both human and environmental), site visits, etc. State any software packages used to analyze data. Methods are the recipe for how the investigation was conducted and will allow for interpretation of the results and conclusions.
• Results - Provide a summary of the (who, what, when, where) of cases; case statuses (confirmed, probable, suspect); demographics (age, sex, race, ethnicity); jurisdiction(s); clinical descriptions (symptoms, duration of symptoms, onset dates, hospitalizations, and deaths); date(s) of specimen(s) collected and all laboratory findings (what was tested, where testing occurred, type of test, test results). Include descriptive and analytical statistics. Also include findings from environmental investigations, onsite visits, or other pertinent information.
• Discussion - Discuss the information included in the results and background to help explain the results of the investigation and the possible associations between the illnesses and possible risk factors. How do the epidemiological, laboratory, and environmental findings mesh with the known epidemiology of the disease? Do the findings support the hypothesis? Provide alternative hypotheses if known. Further describe other interesting or key features of the outbreak and list any limitations for the study.
• Control Measures - Describe any control measures that were recommended or implemented, including restaurant or child care inspections, isolation of cases, etc.
• Conclusion - Make your final statement that the findings of the investigation confirmed (or did not confirm) the existence of an outbreak; what is the suspected cause and source of the outbreak (if able to be determined); and describe how the control measures implemented likely impacted the number of cases seen. Also use this section to describe why the findings of the investigation are significant and how they can be applied to future outbreaks.
• Appendix - Include in this section any tables for summary data or statistical findings which are labeled accordingly and referenced throughout the document, including the epidemic curve. The appendix may also include additional supporting documentation such as inspection reports, notification letters, press releases, etc.
• References - Include in this section any articles sited in the outbreak report using the American Medical Association (AMA) format or American Psychological Association (APA) format.

The approved final report should be distributed to all agencies that contributed to the investigation effort. The report should also be maintained in accordance with record retention laws.