Which study design would provide the most useful information to determine whether alcohol-impregnated caps prevent cross-contamination in IV lines?

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

Answer: (A)

When evaluating whether a preventive device like alcohol-impregnated caps reduces cross-contamination in IV lines, it helps to start from the practical realities of observational study designs. A case-control approach is especially efficient when the adverse outcome is relatively rare. You identify two groups: cases who experienced cross-contamination and controls who did not. Then you look backward to compare how many in each group were exposed to the caps. This setup yields an odds ratio that describes the strength of the association between cap use and the presence or absence of contamination, using existing data and records to determine exposure.

This design is often more feasible in hospital settings than a randomized trial, which, while strong for proving causality, can be difficult to implement ethically and logistically—especially when withholding a potentially protective intervention from a control group. Cross-sectional studies, by contrast, capture exposure and outcome at one time point, so they can’t establish temporality and causation. Cohort studies follow people over time to see who develops contamination, but they usually require larger samples and longer follow-up, which is less efficient for rare events.

So, a case-control approach provides a practical, efficient way to explore whether the caps are associated with reduced cross-contamination, particularly when the outcome is not common and you can reliably ascertain past exposure from records.