Complex surgical site infections and the devilish details of risk adjustment: important implications for public reporting.
OBJECTIVE
To validate the National Nosocomial Infection Surveillance (NNIS) risk index as a tool to account for differences in case mix when reporting rates of complex surgical site infection (SSI).


METHODS
Prospective cohort study.


METHODS
Twenty-four community hospitals in the southeastern United States.


METHODS
We identified surgical procedures performed between January 1, 2005, and June 30, 2007. The Goodman-Kruskal gamma or G statistic was used to determine the correlation between the NNIS risk index score and the rates of complex SSI (not including superficial incisional SSI). Procedure-specific analyses were performed for SSI after abdominal hysterectomy, cardiothoracic procedures, colon procedures, insertion of a hip prosthesis, insertion of a knee prosthesis, and vascular procedures.


RESULTS
A total of 2,257 SSIs were identified during the study period (overall rate, 1.19 SSIs per 100 procedures), of which 1,093 (48.4%) were complex (0.58 complex SSIs per 100 procedures). There were 45 complex SSIs identified following 7,032 abdominal hysterectomies (rate, 0.64 SSIs per 100 procedures); 63 following 5,318 cardiothoracic procedures (1.18 SSIs per 100 procedures); 139 following 5,144 colon procedures (2.70 SSIs per 100 procedures); 63 following 6,639 hip prosthesis insertions (0.94 SSIs per 100 procedures); 73 following 9,658 knee prosthesis insertions (0.76 SSIs per 100 procedures); and 55 following 6,575 vascular procedures (0.84 SSIs per 100 procedures). All 6 procedure-specific rates of complex SSI were significantly correlated with increasing NNIS risk index score (P<.05).


CONCLUSIONS
Some experts recommend reporting rates of complex SSI to overcome the widely acknowledged detection bias associated with superficial incisional infection. Furthermore, it is necessary to compensate for case-mix differences in patient populations, to ensure that intrahospital comparisons are meaningful. Our results indicate that the NNIS risk index is a reasonable method for the risk stratification of complex SSIs for several commonly performed procedures.
Anderson
Deverick J
DJ
Duke Infection Control Outreach Network, Duke University Medical Center, Durham, North Carolina 27710, USA. dja@duke.edu
Chen
Luke F
LF
Sexton
Daniel J
DJ
Kaye
Keith S
KS
D002487:Centers for Disease Control and Prevention, U.S.; D003428:Cross Infection / Q000453:epidemiology / Q000517:prevention & control; D006764:Hospitals, Community / Q000592:standards; D006801:Humans; D019221:Mandatory Reporting; D011159:Population Surveillance / Q000379:methods; D020379:Risk Adjustment / Q000379:methods*; D012307:Risk Factors; D013514:Surgical Procedures, Operative / Q000009:adverse effects* / Q000145:classification*; D013530:Surgical Wound Infection / Q000453:epidemiology* / Q000517:prevention & control*; D014481:United States