Evaluating the Use of the Case Mix Index for Risk Adjustment of Healthcare-Associated Infection Data: An Illustration using Clostridium difficile Infection Data from the National Healthcare Safety Network.
BACKGROUND Case mix index (CMI) has been used as a facility-level indicator of patient disease severity. We sought to evaluate the potential for CMI to be used for risk adjustment of National Healthcare Safety Network (NHSN) healthcare-associated infection (HAI) data. METHODS NHSN facility-wide laboratory-identified Clostridium difficile infection event data from 2012 were merged with the fiscal year 2012 Inpatient Prospective Payment System (IPPS) Impact file by CMS certification number (CCN) to obtain a CMI value for hospitals reporting to NHSN. Negative binomial regression was used to evaluate whether CMI was significantly associated with healthcare facility-onset (HO) CDI in univariate and multivariate analysis. RESULTS Among 1,468 acute care hospitals reporting CDI data to NHSN in 2012, 1,429 matched by CCN to a CMI value in the Impact file. CMI (median, 1.49; interquartile range, 1.36-1.66) was a significant predictor of HO CDI in univariate analysis (P<.0001). After controlling for community onset CDI prevalence rate, medical school affiliation, hospital size, and CDI test type use, CMI remained highly significant (P<.0001), with an increase of 0.1 point in CMI associated with a 3.4% increase in the HO CDI incidence rate. CONCLUSIONS CMI was a significant predictor of NHSN HO CDI incidence. Additional work to explore the feasibility of using CMI for risk adjustment of NHSN data is necessary. Infect. Control Hosp. Epidemiol. 2015;37(1):19-25.
Division of Healthcare Quality Promotion,Centers for Disease Control and Prevention,Atlanta,Georgia.
Nicola D
ND
Thompson
Division of Healthcare Quality Promotion,Centers for Disease Control and Prevention,Atlanta,Georgia.
Jonathan R
JR
Edwards
Division of Healthcare Quality Promotion,Centers for Disease Control and Prevention,Atlanta,Georgia.
Margaret A
MA
Dudeck
Division of Healthcare Quality Promotion,Centers for Disease Control and Prevention,Atlanta,Georgia.
Scott K
SK
Fridkin
Division of Healthcare Quality Promotion,Centers for Disease Control and Prevention,Atlanta,Georgia.
Shelley S
SS
Magill
D016360:Clostridioides difficile; D003015:Clostridium Infections / Q000453:epidemiology*; D003428:Cross Infection / Q000453:epidemiology*; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D011237:Predictive Value of Tests; D015995:Prevalence; D020379:Risk Adjustment / Q000379:methods*; D014481:United States / Q000453:epidemiology