An Analysis of the Standardized Infection Ratio in California From 2015 to 2019: A Publicly Reported, Validated Measure of Hospital Case-Mix Complexity and Quality for Surgical Site Infections in Hip Arthroplasty.

Background: The Standardized Infection Ratio (SIR), developed by the National Healthcare Safety Network (NHSN), is a validated health care quality outcome measure utilized by the California Department of Public Health. Our primary goal was to use information from the SIR as measures of risk-adjusted surgical case-mix complexity and health care-associated infection quality for surgical site infections (SSIs) in hip prosthesis (HPRO) surgery.

Methods: We acquired NHSN SSI data files for HPRO surgery from 330 acute-care hospitals. We categorized hospitals into five types (teaching, rural, community low-volume, community medium-volume, and community high-volume) and sorted hospitals by procedure count, generating volume terciles. We multiplied each SIR and 95% confidence limits (CLs) by a scale factor to allow for a comparison to the average SIR in California for the study period.

Results: The highest and lowest expected infection rates (case-mix complexity) were found in teaching hospital (0.86%) and community, high-volume hospitals (0.56%), respectively. When all nonteaching hospitals were combined, teaching hospitals treated a higher case complexity (95% CL 0.7713 to 0.9727) than non-teaching hospitals (95% CL 0.5774 to 0.6518). The lowest and highest SIR values were seen in community high-volume (0.78) and rural hospitals (1.38). The lowest-volume hospitals performed significantly worse (SIR 1.15: 95% CL 1.058 to 1.256) than the highest-volume hospitals (SIR 0.83: 95% CL 0.747 to 0.920).

Conclusions: The SIR model developed by NHSN provides important public information about risk-adjusted surgical case-mix complexity and hospital quality for SSIs that incorporates parameters that may more accurately account for technical challenges in HPRO surgery.