During the analytic phase of an outbreak investigation, what is the main activity?

• A. Evaluate plausibility of hypotheses using differential list
• B. Formulate hypotheses
• C. Plan interventions
• D. Vaccinate population

Answer: (A)

The analytic phase focuses on testing ideas by weighing how well different explanations fit the observed data. The main activity is to evaluate the plausibility of competing hypotheses by building a differential list—a set of potential sources, exposures, and transmission routes—and then assessing, with the data, which items are supported or refuted. This involves looking at patterns in who was affected, when and where cases occurred, and which exposures are more common among cases than controls or non-cases, using these clues to narrow down the most likely cause. Hypothesis generation typically happens earlier in the investigation, while planning interventions and vaccination are actions taken after a likely cause is identified and confirmed. The analytic phase, therefore, is about rigorously testing and prioritizing explanations based on the evidence.