title: Surgical Site Infections: Volume-Outcome Relationship and Year-to-Year Stability of Performance Rankings.
abstract: BACKGROUND
  Surgical site infection (SSI) rates are publicly reported as quality metrics and increasingly used to determine financial reimbursement.
  
  
  OBJECTIVE
  To evaluate the volume-outcome relationship as well as the year-to-year stability of performance rankings following coronary artery bypass graft (CABG) surgery and hip arthroplasty.
  
  
  METHODS
  We performed a retrospective cohort study of Medicare beneficiaries who underwent CABG surgery or hip arthroplasty at US hospitals from 2005 to 2011, with outcomes analyzed through March 2012. Nationally validated claims-based surveillance methods were used to assess for SSI within 90 days of surgery. The relationship between procedure volume and SSI rate was assessed using logistic regression and generalized additive modeling. Year-to-year stability of SSI rates was evaluated using logistic regression to assess hospitals' movement in and out of performance rankings linked to financial penalties.
  
  
  RESULTS
  Case-mix adjusted SSI risk based on claims was highest in hospitals performing <50 CABG/year and <200 hip arthroplasty/year compared with hospitals performing ≥200 procedures/year. At that same time, hospitals in the worst quartile in a given year based on claims had a low probability of remaining in that quartile the following year. This probability increased with volume, and when using 2 years' experience, but the highest probabilities were only 0.59 for CABG (95% confidence interval, 0.52-0.66) and 0.48 for hip arthroplasty (95% confidence interval, 0.42-0.55).
  
  
  CONCLUSIONS
  Aggregate SSI risk is highest in hospitals with low annual procedure volumes, yet these hospitals are currently excluded from quality reporting. Even for higher volume hospitals, year-to-year random variation makes past experience an unreliable estimator of current performance.
authors: *Division of Infectious Diseases, Brigham and Women's Hospital †Department of Population Medicine, Harvard Medical School and Harvard Pilgrim Health Care Institute, Boston ‡Department of Biostatistics and Epidemiology, University of Massachusetts Amherst School of Public Health and Health Sciences, Amherst, MA §Division of Infectious Diseases, University of California Irvine School of Medicine, Orange, CA.
authors: Michael S
authors: MS
authors: Calderwood
authors: Ken
authors: K
authors: Kleinman
authors: Susan S
authors: SS
authors: Huang
authors: Michael V
authors: MV
authors: Murphy
authors: Deborah S
authors: DS
authors: Yokoe
authors: Richard
authors: R
authors: Platt
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D001026:Coronary Artery Bypass / Q000009:adverse effects*; D005260:Female; D061847:Hospitals, High-Volume / Q000592:standards / Q000706:statistics & numerical data*; D061846:Hospitals, Low-Volume / Q000592:standards / Q000706:statistics & numerical data*; D006801:Humans; D016015:Logistic Models; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data; D019984:Quality Indicators, Health Care; D012189:Retrospective Studies; D013530:Surgical Wound Infection / Q000453:epidemiology* / Q000209:etiology; D014481:United States / Q000453:epidemiology