The correct answer is C, "Rate of multi-drug resistant organisms acquisition," as it represents an example of an outcome measure. According to the Certification Board of Infection Control and Epidemiology (CBIC) guidelines, outcome measures are indicators that reflect the impact or result of infection prevention and control interventions on patient health outcomes or the incidence of healthcare-associated infections (HAIs). The rate of multi-drug resistant organisms (MDRO) acquisition directly measures the incidence of new infections caused by resistant pathogens, which is a key outcome affected by the effectiveness of infection control practices (CBIC Practice Analysis, 2022, Domain II: Surveillance and Epidemiologic Investigation, Competency 2.4 - Evaluate the effectiveness of infection prevention and control interventions).

Option A (hand hygiene compliance rate) is an example of a process measure, which tracks adherence to specific protocols or practices intended to prevent infections, rather than the resulting health outcome. Option B (adherence to environmental cleaning) is also a process measure, focusing on the implementation of cleaning protocols rather than the end result, such as reduced infection rates. Option D (timing of preoperative antibiotic administration) is another process measure, assessing the timeliness of an intervention to prevent surgical site infections, but it does not directly indicate the outcome (e.g., infection rate) of that intervention.

Outcome measures, such as the rate of MDRO acquisition, are critical for evaluating the success of infection prevention programs and are often used to guide quality improvement initiatives. This aligns with CBIC’s emphasis on using surveillance data to assess the effectiveness of interventions and inform decision-making (CBIC Practice Analysis, 2022, Domain II: Surveillance and Epidemiologic Investigation, Competency 2.5 - Use data to guide infection prevention and control strategies). The focus on MDRO acquisition specifically highlights a significant healthcare challenge, making it a prioritized outcome measure in infection control.