A nutrition support team wants to determine whether patients who receive total parenteral nutrition (TPN)...

The CBIC Certified Infection Control Exam Study Guide (6th edition) emphasizes that accurate comparison of healthcare-associated infection risk between groups requires use of standardized, exposure-based rates. For central line–associated bloodstream infections (CLABSIs), the recommended metric is infections per 1,000 central line days, which accounts for the amount of time patients are actually exposed to the risk factor—in this case, the presence of a central venous catheter.

Patients receiving TPN at home and those receiving TPN in the hospital may differ substantially in duration of catheter use, care practices, and patient acuity. Simply comparing percentages or raw numbers of infections fails to adjust for differences in central line utilization and can result in misleading conclusions. By using central line days as the denominator, infection rates are normalized and allow for valid comparisons between populations and settings.

Option A does not account for differences in exposure time. Option C compares different time periods rather than comparing risk between groups. Option D provides a ratio but lacks standardization and is not consistent with accepted surveillance methodology.

The Study Guide reinforces that device-associated infection surveillance—such as CLABSI monitoring—must use device days to assess true risk and guide prevention strategies. Understanding and applying correct epidemiologic measures is a core competency for infection preventionists and a frequently tested concept on the CIC® exam.

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