SIR: Standardized Infection Ratio
The Standardized Infection Ratio is the CDC NHSN-defined metric for healthcare-associated infections. SIR = observed infections / expected infections (calculated from NHSN risk-adjustment models). SIR < 1.0 means better than national benchmark; > 1.0 means worse.
Which infections SIR covers
Standard CMS-required SIRs: Central Line-Associated Bloodstream Infection (CLABSI), Catheter-Associated Urinary Tract Infection (CAUTI), Surgical Site Infection (SSI) — typically tracked separately for colon surgery and abdominal hysterectomy in the HAC Reduction Program — Methicillin-Resistant Staphylococcus Aureus (MRSA) bacteremia, and Clostridioides difficile (C. diff) Lab-Identified Events.
Where SIR appears in payment
Each HAI SIR is reported through NHSN. CMS uses them in the HAC Reduction Program (1% Medicare DRG penalty for bottom-quartile performers), Hospital VBP (HAI domain), and Care Compare public reporting. Many state Medicaid programs use SIR for hospital-specific Medicaid quality measurement.
Where Vizier fits
Vizier reads infection surveillance data + denominator data (line days, urinary catheter days, surgical procedure counts) from your EHR / infection control system and computes SIR continuously by unit. The trend chart surfaces emerging infection control gaps in time to act, rather than at the next quarterly NHSN data submission.