The CBIC Certified Infection Control Exam Study Guide (6th edition) follows the standardized surveillance methodology used for calculating central line days, which is essential for accurate reporting of central line–associated bloodstream infection (CLABSI) rates. A central line day is counted for each patient who has one or more central lines in place at the time of the daily count, regardless of the number of central lines present.

Therefore, if a patient has more than one central line, the patient is still counted as one central line day, making option C the correct statement. This approach ensures consistency and comparability of CLABSI rates across units and facilities.

Option A is incorrect because tunneled central venous catheters and implanted ports are included in central line counts if they meet the definition of a central line. Option B is incorrect because a central line is counted on any day it is present, even if it has been in place for less than 24 hours. Option D is incorrect because peripheral intravenous lines are not central lines and must never be included in central line day counts.

Accurate calculation of device days is a foundational surveillance competency for infection preventionists. Understanding these definitions is critical for valid CLABSI rate calculation, benchmarking, and performance improvement and is a frequently tested concept on the CIC® exam.