To study exposure factors in an outbreak with clearly defined cases, which study design is commonly employed?

• A. Prospective cohort study
• B. Cross-sectional study
• C. Case-control study
• D. Randomized trial

Answer: (C)

When investigating an outbreak with clearly defined cases, a case-control design is most efficient for identifying exposure factors. You start with those who became ill (the cases) and compare them to a similar group who did not become ill (the controls), looking backward to see what exposures occurred during the relevant risk period. This approach is well suited to outbreaks or rare diseases because it requires fewer participants and directly yields an odds ratio that quantifies the association between exposure and illness. It’s also faster and less costly than following a large cohort. Cross-sectional designs don’t establish temporality well, and randomized trials aren’t ethical or practical for outbreak investigations since you wouldn’t assign exposures.