During the descriptive phase of an outbreak investigation, which activity is typical?

• A. Formulate testable hypotheses as to the source, identify, and mode of transmission
• B. Analyze data for plausibility
• C. Develop short-term plans
• D. Implement mass vaccination

Answer: (A)

In the descriptive phase, you’re building the picture of who was affected, where, and when, and you begin turning those observations into plausible explanations about what caused the outbreak and how it spread. Formulating testable hypotheses about the source and the mode of transmission fits this stage because it uses the pattern in the data to propose explanations that can be examined with further data collection and analysis. The other activities—analyzing data for plausibility, developing short-term plans, and implementing mass vaccination—are more aligned with later analytic and response steps, not the initial descriptive work.