Skip to main content Accessibility help

Improving Risk-Adjusted Measures of Surgical Site Infection for the National Healthcare Safely Network

  • Yi Mu (a1), Jonathan R. Edwards (a1), Teresa C. Horan (a1), Sandra I. Berrios-Torres (a1) and Scott K. Fridkin (a1)...



The National Healthcare Safety Network (NHSN) has provided simple risk adjustment of surgical site infection (SSI) rates to participating hospitals to facilitate quality improvement activities; improved risk models were developed and evaluated.


Data reported to the NHSN for all operative procedures performed from January 1, 2006, through December 31, 2008, were analyzed. Only SSIs related to the primary incision site were included. A common set of patient- and hospital-specific variables were evaluated as potential SSI risk factors by univariate analysis. Some ific variables were available for inclusion. Stepwise logistic regression was used to develop the specific risk models by procedure category. Bootstrap resampling was used to validate the models, and the c-index was used to compare the predictive power of new procedure-specific risk models with that of the models with the NHSN risk index as the only variable (NHSN risk index model).


From January 1, 2006, through December 31, 2008, 847 hospitals in 43 states reported a total of 849,659 procedures and 16,147 primary incisional SSIs (risk, 1.90%) among 39 operative procedure categories. Overall, the median c-index of the new procedure-specific risk was greater (0.67 [range, 0.59–0.85]) than the median c-index of the NHSN risk index models (0.60 [range, 0.51–0.77]); for 33 of 39 procedures, the new procedure-specific models yielded a higher c-index than did the NHSN risk index models.


A set of new risk models developed using existing data elements collected through the NHSN improves predictive performance, compared with the traditional NHSN risk index stratification.


Corresponding author

1600 Clifton Road NE MS A-24, Atlanta, GA 30329-4018 (


Hide All
1. Klevens, RM, Edwards, JR, Richards, CL Jr, et al. Estimating health care–associated infections and deaths in U.S. hospitals. Public Health Reports 2002;122:160167.
2. Mangram, AJ, Horan, TC, Pearson, ML, Silver, LC, Jarvis, WR. Guideline for prevention of surgical site infection. Infect Control Hosp Epidemiol 1999;20:250280.
3. Scott, RD II. The direct medical costs of healthcare-associated infections in U.S. hospitals and the benefits of prevention. 2009. Accessed August 12, 2011.
4. Haley, RW, Culver, DH, White, JW, et al. The efficacy of infection surveillance and control programs in preventing nosocomial infections in United States hospitals. Am J Epidemiol 1985;121:182205.
5. Gaynes, R, Richards, C, Edwards, JR, et al. Feeding back surveillance data to prevent hospital-acquired infections. Emerg Infect Dis 2001;7:295298.
6. Brandt, C, Hansen, S, Sohr, D, Daschner, F, Ruden, H, Gastmeier, P. Finding a method for optimizing risk adjustment when comparing surgical-site infecions rates. Infect Control Hosp Epidemiol 2004;25:1318.
7. Anderson, DJ, Kaye, KS, Classen, D, et al. Strategies to prevent surgical site infections in acute care hospitals. Infect Control Hosp Epidemiol 2008;(suppl 1):S51S61.
8. Culver, DH, Horan, TC, Gaynes, RP, et al. Surgical wound-infection rates by wound class, operative procedure, and patient risk index. Am J Med 1991;91:S152S157.
9. American Society of Anesthesiologists (ASA). ASA physical status classification system, Accessed March 2, 2011.
10. US Department of Health and Human Services (HHS). HHS action plan to prevent healthcare associated infections: appendices. Appendix G. Accessed July 28, 2010.
11. Anderson, DJ, Chen, LF, Sexton, DJ, Kaye, KS. Complex surgical site infections and the devilish details of risk adjustment: important implications for public reporting. Infect Control Hosp Epidemiol 2008;29:941946.
12. Shahian, DM, O'Brien, SM, Filardo, G, Ferraris, VA, Haan, CK, Rich, JB, et al. The Society of Thoracic Surgeons 2008 cardiac surgery risk models: part 1—coronary artery bypass grafting surgery. Ann Thome Surg 2009;88:S2S22.
13. Friedman, ND, Bull, AL, Russo, PL, Gurrin, L, Richards, M. Performance of the National Nosocomial Infections Surveillance risk index in predicting surgical site infection in Australia. Infect Control Hosp Epidemiol 2007;28:5559.
14. Paul, M, Raz, A, Leibovici, L, Madar, H, Holinger, R, Rubinovitch, B. Sternal wound infection after coronary artery bypass graft surgery: validation of existing risk scores. J Thorac Cardiovasc Surg 2007;133:397403.
15. Roy, MC, Herwaldt, LA, Embrey, R, Kuhns, K, Wenzel, RP, Eerl, TM. Does the Centers for Disease Control's NNIs system risk index stratify patients undergoing cardiothoracic operations by their risk of surgical-site infection. Infect Control Hosp Epidemiol 2000;21:186190.
16. Edwards, JR, Peterson, KD, Mu, Y, et al. National Healthcare Safety Network (NHSN) report: data summary for 2006 through 2008, issued December 2009. Am J Infect Control 2009;37: 783805.
17. Association for Professionals in Infection Control. HAI reporting laws and regulation, Accessed August 12, 2011.
18. Centers for Disease Control and Prevention. National Health-care Safety Network: surgical site infection (SSI) event, Accessed June 26, 2010.
19. National Quality Forum. National voluntary consensus standards for the reporting of healthcare-associated infections data. National Quality Forum, 2008. _Standards_for_the_Reporting_of_Healthcare-Associated_Infection_Data.aspx. Accessed August 9, 2010.
20. Hanley, JA, McNeil, BJ. The meaning and use of the area under a receive operating characteristic (ROC) curve. Radiology 1982; 143:2936.
21. Hanley, JA, McNeil, BJ. A method of comparing the areas under receiver operating characteristic curves derived from the same cases. Radiology 1983;148:839843.
22. Abboud, CS, Wey, SB, Baltar, VT. Risk factors for mediastinitis after cardiac surgery. Ann Thorac Surg 2004;77:676683.
23. de Boer, AS, Mintjes-de Groot, AJ, Severijnen, AJ, van den Berg, JM, van Pelt, W. Risk assessment for surgical-site infections in orthopedic patients. Infect Control Hosp Epidemiol 1999;20: 402407.
24. Gaynes, RP. Surgical-site infections (SSI) and the NNIS SSI risk index, part II: room for improvement. Infect Control Hosp Epidemiol 2001;22:268272.
25. The Parisian Mediastinitis Study Group. Risk factors for deep sternal wound infections after sternotomy: a prospective, multicenter study. J Thorac Cardiovasc Surg 2006;111:12001207.
26. Harrignton, G, Russo, P, Spelman, D, et al. Surgical-site infection rates and risk factor analysis in coronary artery bypass graft surgery. Infect Control Hosp Epidemiol 2004;25:472476.
27. Killian, CA, Graffunder, EM, Vinciguerra, TJ, Venezia, RA. Risk factors for surgical-site infections following cesarean section. Infect Control Hosp Epidemiol 2001;22:613617.
28. Kivi, M, Mannien, J, Wille, JC, van den Hof, S. Surgical site infection surveillance and the predictive power of the National Nosocomial Infection Surveillance index as compared with alternative determinants in the Netherlands. Am J Infect Control 2008;36:S27S31.
29. Neumayer, L, Hosokawa, P, Itani, K, El-Tamer, M, Henderson, WG, Khuri, SF. Multivariable predictors of postoperative surgical site infection after general and vascular surgery: results from the patient safety in surgery study. J Am Coll Surg 2007;204: 11781187.
30. Olsen, MA, Lock-Buckley, P, Hopkins, D, Polish, LB, Sundt, TM, Fraser, VJ. The risk factors for deep and superficial chest surgical-site infections after coronary artery bypass graft surgery are different. J Thorac Cardiovasc Surg 2002;124:136145.
31. Russo, PL, Spelman, DW. A new surgical-site infection risk index using risk factors identified by multivariate analysis for patients undergoing coronary artery bypass graft surgery. Infect Control Hosp Epidemiol 2002;23:372376.
32. Tran, TS, Jamulitrat, S, Chongsurvivatwong, V, Geater, A. Risk factors for postcesarean surgical site infection. Obstet Gynecol 2000;95:367371.
33. Geubbels, ELPE, Grobbee, DE, Vandenbroucke-Grauls, CMJE, Wille, JC, de Boer, AS. Improved risk adjustment for comparison of surgical site infection rates. Infect Control Hosp Epidemiol 2006;27:13301339.

Related content

Powered by UNSILO

Improving Risk-Adjusted Measures of Surgical Site Infection for the National Healthcare Safely Network

  • Yi Mu (a1), Jonathan R. Edwards (a1), Teresa C. Horan (a1), Sandra I. Berrios-Torres (a1) and Scott K. Fridkin (a1)...


Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed.