The 10 steps field epidemiologists follow, and how each one feeds the next
A real outbreak investigation almost never happens in a neat straight line; investigators loop back and repeat steps constantly as new clues arrive. This guide organizes the whole process into 10 steps (the Science Olympiad Disease Detectives wiki's condensed version of CDC's outbreak-investigation framework), and knowing their order (and why that order matters) is one of the most-tested skills in this event.
Gather equipment, confirm authority to investigate, and arrange the right expertise and supplies before heading out.
Compare the current case count to what's normally expected (the endemic baseline): is this really more cases than usual?
Confirm that the illness has actually been correctly diagnosed, using lab tests when possible: ruling out lab error or misdiagnosis.
Set clear, standard criteria (using person, place, and time: see Section 3) so every investigator counts cases the same way, then actively search for every case that fits and record consistent details (symptoms, exposures, dates) on each one. When testing contacts of a contagious person (a TB contact investigation, for example), work in concentric circles: test the closest, longest contacts first, and widen the circle only if many of them are infected.
Organize every case by time, place, and person to describe the outbreak's shape: this is where epi curves and maps come in.
Based on the descriptive picture, propose specific, testable explanations: the likely agent, source, and mode of transmission.
Run an analytic study (usually case-control or cohort) and calculate rates, risks, or odds to see if the data actually supports a hypothesis.
If the numbers don't support the first idea, go back to the data (or the field) and generate a better one, and check that the conclusion lines up with laboratory findings (like matching pathogen fingerprints) and environmental inspections: looping back here is normal, not failure.
Act on the findings: often this starts even earlier, as soon as a likely source is identified, and keep watching afterward (surveillance) to confirm the outbreak is truly over and to catch any flare-up quickly.
Share results with health officials, the public, and the scientific community: usually through a written report.
| CDC # | CDC Step | SciOly # | SciOly Step |
|---|---|---|---|
| 1 | Prepare for field work | 1 | Prepare for field work |
| 2 | Establish the existence of an outbreak | 2 | Establish the existence of an outbreak |
| 3 | Verify the diagnosis | 3 | Verify the diagnosis |
| 4 | Construct a working case definition | 4 | Define & identify cases |
| 5 | Find cases systematically and record information | 4 | Define & identify cases |
| 6 | Perform descriptive epidemiology (time, place, person) | 5 | Describe by time, place & person |
| 7 | Develop hypotheses | 6 | Develop hypotheses |
| 8 | Evaluate hypotheses epidemiologically | 7 | Evaluate hypotheses |
| 9 | Reconsider, refine and re-evaluate hypotheses | 8 | Refine hypotheses & carry out additional studies |
| 10 | Compare and reconcile with laboratory and environmental studies | 8 | Refine hypotheses & carry out additional studies |
| 11 | Implement control and prevention measures | 9 | Implement control & prevention measures |
| 12 | Initiate or maintain surveillance | 9 | Implement control & prevention measures |
| 13 | Communicate findings | 10 | Communicate findings |