Validation of a modified version of the national nosocomial infections surveillance system risk index for health services research.
OBJECTIVE
To validate the National Nosocomial Infections Surveillance system risk index through administrative data to predict surgical site infections.


METHODS
Retrospective cohort study.


METHODS
Population-based analysis in Ontario, Canada.


METHODS
All elderly patients who underwent elective surgery from April 1, 1992, through March 31, 2006 (n = 469,349).


METHODS
Data on procedural and patient outcomes were gathered from linked population-wide hospital discharge records and physician claims. The 75th percentile of surgical duration was estimated through anesthesiologist billing fees recorded in 15-minute increments; the American Society of Anesthesiology score of at least 3 out of 5 was estimated by diagnostic codes for severe systemic illness; and all surgeries were classified as clean or clean-contaminated because of their elective nature (thus, the maximum score on the modified index was 2).


RESULTS
A total of 147,216 surgeries (31%) had a score of 0; 246,592 (53%) had a score of 1; and 75,541 (16%) had a score of 2 on the modified index. The 30-day risk of surgical site infection increased with each increment in the modified index (score of 0, 5.4%; score of 1, 8.0%; score of 2, 14.3%; P < .001). The association was evident for surgical site infection diagnosed during the index admission (score of 0, 2.0%; score of 1, 3.7%; score of 2, 8.9%; P < .001), as well as that associated with reoperation or death (score of 0, 0.04%; score of 1, 0.23%; score of 2, 0.73%; P < .001). The modified index predicted increases in surgical site infection risk within each of 11 surgical subgroups. In accord with past research, the modified index had modest discrimination (C statistic, 0.59), and the majority of surgical site infections (72%) occurred within lower risk strata.


CONCLUSIONS
The modified index predicts surgical site infection in population-based analyses and is associated with incremental increases in risk.
Daneman
Nick
N
Institute for Clinical Evaluative Sciences, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada. nick.daneman@sunnybrook.ca
Simor
Andrew E
AE
Redelmeier
Donald A
DA
D000368:Aged; D000369:Aged, 80 and over; D003428:Cross Infection / Q000453:epidemiology*; D017558:Elective Surgical Procedures / Q000009:adverse effects*; D006302:Health Services Research / Q000379:methods*; D006801:Humans; D015994:Incidence; D009864:Ontario / Q000453:epidemiology; D011159:Population Surveillance / Q000379:methods*; D018570:Risk Assessment / Q000379:methods*; D013530:Surgical Wound Infection / Q000453:epidemiology*