The Centers for Medicare and Medicaid Services (CMS) use colon surgical site infection (SSI) rates to rank hospitals and apply financial penalties. CMS's risk adjustment model omits potentially impactful variables that might disadvantage hospitals with complex surgical populations.
We analyzed adult patients who underwent colon surgery within facilities associated with HCA Healthcare from 2014 to 2016. SSIs were identified from National Health Safety Network (NHSN) reporting. We trained and validated three SSI prediction models using 1) current CMS model variables, including hospital-specific random effects (HCA-adapted-CMS), 2) demographics and claims-based comorbidities (expanded-claims), and 3) demographics, claims-based comorbidities, and NHSN variables (claims-plus-EHR). Discrimination, calibration, and resulting rankings were compared among all models and the current CMS model with published coefficient values (CMS).
We identified 39,468 colon surgeries in 149 hospitals resulting in 1,216 (3.1%) SSIs. Compared to the HCA-adapted-CMS model, the expanded-claims model had similar performance (c-statistic 0.65 vs 0.67), while the claims-plus-EHR model was more accurate (c-statistic 0.70, 95% CI: 0.67-0.73; p=0.004). The sampling variation due to low surgical volume and small number of infections contributed 74% of the total variation in observed SSI rates between hospitals. When CMS model rankings were compared to those from the expanded-claims and claims-plus-EHR models, eighteen (15%) and 26 (22%) hospitals changed quartiles, and 10 (8.3%) and 12 (10%) hospitals changed into or out of the lowest-performing quartile, respectively.
An expanded set of variables improved colon SSI risk prediction and quartile assignment, but low procedure volumes and SSI events remain a barrier to effectively compare hospitals.