Hospital antibiotic use · NHSN measures
Inpatient antibiotic-use measures depend on patient-care location, antimicrobial category, reporting completeness and risk adjustment. A ratio or days-of-therapy rate is a stewardship signal, not a self-explanatory hospital ranking.
Two measures answer different questions
The CDC National Healthcare Safety Network Antimicrobial Use option collects standardized facility data. Days of therapy count days on which a patient receives a reportable antimicrobial, while use rates place those days over a defined denominator such as days present or admissions, depending on the measure and location.
The Standardized Antimicrobial Administration Ratio, or SAAR, compares observed antimicrobial days with predicted antimicrobial days for a specified agent category and patient-care context. CDC describes SAARs as risk-adjusted summary measures. The result depends on the applicable baseline and model.
Interpretation also needs a defined comparison question. A stewardship team may examine change within one location, variation across agent categories or performance against a national model; those analyses are not interchangeable.
Why a single number cannot rank hospitals
- Facilities may serve different patient populations and clinical services.
- Location mapping changes which encounters and denominators are included.
- Agent categories answer narrower questions than total antibiotic use.
- Incomplete or invalid submissions can distort interpretation.
- A SAAR does not establish that any individual prescription was inappropriate.
CDC updated the national antimicrobial-use baseline and risk-adjustment models for the 2023 SAAR rebaseline. Values generated under different baselines should not be presented as directly comparable without the agency’s method.
A reproducible reporting card
- Name the NHSN report, facility or group scope and data period.
- Record location, agent category, numerator and denominator.
- Identify SAAR baseline and risk-adjustment version if used.
- Document data-quality checks and missing reporting periods.
- Pair the metric with local clinical review before judging use.
What the metric cannot decide
Aggregate data can guide an antimicrobial-stewardship investigation. They cannot diagnose infection, select a medicine or determine whether a patient should continue therapy. Those questions require individual clinical information and qualified review.