Documenting the outbreak: Chronologies

An outbreak chronology, or timeline of events, is a record of the important events that occurred during an outbreak investigation. There are two general types:

  1. Tabular or text-based: detailed summary of all important events occurring each day during the outbreak investigation.
  2. Visual: includes only main events plotted on an epidemic curve.

Question 4-3: What events should be included in a chronology?

  • Number of cases by case type (for each date in the chronology)
  • Investigation steps (e.g., date outbreak identified, date lead agency notified, date outbreak declared, date traceback begins, date hypothesis-generation begins, date(s) of results (laboratory, traceback, epidemiologic), date of OICC activation/deactivation, date an epidemiologic assessment is prepared, date outbreak declared over)
  • Date(s) of public health action: risk communication to the public, awareness campaigns, recall of products, and closure of establishment.
  • See the example (text-based) chronology for this investigation (Module 4 – Chronology), as well as the (visual) timeline of events (Module 4 – Visual chronology).