An infection preventionist evaluating a cluster of Clostridioides difficile infection on the alternate level of care unit to determine an association with antibiotic use; which analytical study design is best?

• A. Case-control
• B. Cohort
• C. Cross-sectional
• D. Randomized trial

Answer: (A)

When exploring whether antibiotic exposure is linked to a cluster of Clostridioides difficile infections, a case-control study is the most efficient approach. You start by identifying patients who developed CDI (cases) and similar patients who did not (controls) on the same unit, then look back to compare prior antibiotic exposure between the two groups. This setup is ideal because CDI is a relatively uncommon outcome, so studying cases and matched controls allows you to estimate the association without needing to follow a huge cohort. It also lets you examine multiple antibiotic exposures and adjust for confounders more feasibly in this retrospective context. In contrast, following a large group to see who develops CDI (cohort) can be resource-intensive, a single-time-point survey (cross-sectional) can't establish temporality, and randomly assigning antibiotics (a randomized trial) would be unethical and impractical for this question.