Which statement correctly describes a case-control study in outbreak investigations?

• A. Prospective cohort
• B. Randomized trial
• C. Time-series analysis
• D. Retrospective study comparing exposures between cases and controls

Answer: (D)

A case-control study in outbreak investigations is a retrospective design that starts with who got sick (cases) and who didn’t (controls) and looks back to compare their prior exposures. This approach quickly identifies factors more common among cases, pointing to potential sources or routes of transmission. Because you begin with disease status and examine past exposures, you typically calculate an odds ratio to measure the association between exposure and illness. This design is especially efficient for outbreaks where the disease is rare or time is limited. It isn’t a prospective cohort study (which follows exposed and unexposed groups forward in time), it isn’t a randomized trial (which assigns exposures), and it isn’t a time-series analysis (which tracks case counts over time to detect trends).