The Standardized Antimicrobial Administration Ratio: A New Metric for Measuring and Comparing Antibiotic Use

To provide a standardized, risk-adjusted method for summarizing antibiotic use (AU), enable hospitals to track their AU over time and compare their AU data to national benchmarks, the Centers for Disease Control and Prevention developed the Standardized Antimicrobial Administration Ratio (SAAR).

Hospitals reporting to the National Healthcare Safety Network (NHSN) AU Option collect and submit aggregated AU data electronically as antimicrobial days of therapy per patient days present. SAARs were developed for specific NHSN adult and pediatric patient care locations and cover five antimicrobial agent categories: (1) broad-spectrum agents predominantly used for hospital-onset/multi-drug resistant bacteria; (2) broad-spectrum agents predominantly used for community-acquired infections; (3) anti-methicillin-resistant Staphylococcus aureus agents; (4) agents predominantly used for surgical site infection prophylaxis; and (5) all antibiotic agents. The SAAR is an observed-to-predicted use ratio where predicted use is estimated from a statistical model; a SAAR of 1 indicates that observed use and predicted use are equal.

Most location-level SAARs were statistically significantly different than 1: adult locations up to 52% lower than 1 and up to 41% higher than 1. Median SAARs in adult and pediatric ICUs had a range of 0.667-1.119. SAAR distributions serve as an external comparison to national SAARs.

This is the first aggregate AU metric that uses point-of-care, antimicrobial administration data electronically reported to a national surveillance system to enable risk-adjusted, AU comparisons across multiple hospitals. Endorsed by the National Quality Forum, SAARs provide AU benchmarks that stewardship programs can use to help drive improvements.