Improving the Measurement of Surgical Site Infection Risk Stratification/Outcome Detection

Appendix V. JAMIA Draft Manuscript Tables

Table 1. Number of Procedures Stratified by Hospital and Types between 2008 and 2009

  DH IH VA SLCHCS VVMC
Procedure   Num. % Proc. Num. % Proc. Num. % Proc. Num. % Proc.
CABG Total Procedures 0   1845   78   0  
    sSSI 0   12 0.7% 3 3.8% 0  
    dSSI 0   7 0.4% 0 0.0% 0  
    oSSI 0   1 0.1% 0 0.0% 0  
  Total SSI 0   20 1.1% 3 3.8% 0  
HERNIA Total Procedures 898   1059   237   294  
    sSSI 4 0.4% 0 0.0% 2 0.8% 1 0.3%
    dSSI 2 0.2% 0 0.0% 0 0.0% 0 0.0%
    oSSI 1 0.1% 0 0.0% 1 0.4% 0 0.0%
  Total SSI 7 0.8% 0 0.0% 3 1.3% 1 0.3%
THA Total Procedures 268   2810   90   137  
    sSSI 2 0.7% 0 0.0% 0 0.0% 0 0.0%
    dSSI 2 0.7% 5 0.2% 0 0.0% 1 0.7%
    oSSI 3 1.1% 3 0.1% 2 2.2% 0 0.0%
  Total SSI 7 2.6% 8 0.3% 2 2.2% 1 0.7%
TKA Total Procedures 232   7897   163   421  
    sSSI 1 0.4% 6 0.1% 0 0.0% 0 0.0%
    dSSI 2 0.9% 7 0.1% 0 0.0% 1 0.2%
    oSSI 1 0.4% 2 0.0% 1 0.6% 0 0.0%
  Total SSI   4 1.7% 15 0.2% 1 0.6% 1 0.2%

Abbreviations: CABG, coronary artery bypass grafting; HERNIA, herniorraphy; TKA, total knee arthroplasty; THA, total hip arthroplasty; sSSI, superficial SSI; dSSI, deep SSI; oSSI, organ space SSI

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Table 2. Component rules of the rpart, inclusive, and simple algorithms

CABG All of the following:
Presence of a post-operative culture, and
Post-operative antibiotics were given, and
Maximum post-operative leukocyte count is not less than 11.85
Herniorrhaphy Either of the following:
Presence of a post-operative culture and
   Maximum post-operative leukocyte count is not less than 7.78
Absence of a post-operative culture and one of the following criteria:
   Post-operative antibiotics given and any post-operative leukocyte count test drawn
   Post-operative antibiotics not given, but the patient had a post-operative admission
Total Knee Arthroplasty: Either of the following:
Presence of a post-operative culture, or
Presence of a c-reactive protein and the maximum post-operative leukocyte count is not less than 9.45
Total Hip Arthroplasty: All of the following:
Presence of a post-operative culture, and
Post-operative antibiotics were given, and
Maximum post-operative leukocyte count is not less than 7.55
“Inclusive” algorithm: Any one of the following:
Erythrocyte sedimentation rate greater than 20, or
Total neutrophil count greater than 5,000/mm3, or
Total leukocyte count greater than 9,000/mm3, or
C-reactive protein greater than 3mg/dL, or
Any post-operative antibiotics given, or
Presence of a post-operative culture, or
Patient was readmitted within 30 days post-operatively
“Simple” algorithm: Either of the following:
Microbiology test ordered between post-operative days 4 and 30 (inclusive), or
An antibacterial was prescribed between post-operative days 4 and 30 (inclusive)

Abbreviations: CABG, coronary artery bypass grafting

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Table 3. Performance of Different Algorithms by SSI Type on the Training Set.

  Total Surgeries sSSI dSSI oSSI
Total 35551 374 106 38
  # Flagged (% Total)
 
# True Positives Caught (% Sensitivity)
Rpart Algorithm 2709 (7.6%) 156 (41.7%) 101 (95.3%) 34 (89.5%)
Inclusive Algorithm 7961 (22.4%) 328 (87.7%) 104 (98.1%) 35 (92.1%)
Simple 6939 (19.5%) 318 (85.0%) 103 (97.2%) 34 (89.5%)

Abbreviations: SSI = surgical site infection. sSSI = superficial SSI. dSSI = deep SSI. oSSI = organ-space SSI

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Table 4. Performance of Different Algorithms by SSI Type on the Test Set.

  Total Surgeries sSSI dSSI oSSI
Total 27,739 279 75 33
  # Flagged (% Total)
 
# True Positives Caught (% Sensitivity)
Rpart Algorithm 2034 (7.3%) 126 (45.2%) 54 (72.0%)) 25 (75.8%)
Inclusive Algorithm 8,685 (31.3%) 251 (90.0%) 75 (100%) 30 (90.9%)
Simple 5318 (19.2%) 230 (82.4%) 68 (90.7%) 30 (90.9%)

Abbreviations: SSI = surgical site infection. sSSI = superficial SSI. dSSI = deep SSI. oSSI = organ-space SSI.

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Table 5. Accuracy of algorithm at each participating hospital

Accuracy of Algorithm at DH Accuracy of Algorithm at IH
    Routine Surveillance       Routine Surveillance  
Algo   SSI no SSI Total Algo   SSI no SSI Total
SSI 6 71 77 SSI 9 704 713
no SSI 7 1345 1352 no SSI 16 10857 10873
Total 13 1416 1429 Total 25 11561 11586
                   
  Sensitivity 46.2%   Sensitivity 36.0%
  Specificity 95.0%   Specificity 93.7%
  Positive Predictive Value 7.8%   Positive Predictive Value 1.3%
  Negative Predictive Value 99.5%   Negative Predictive Value 99.9%
Accuracy of Algorithm at VA SLCHCS Accuracy of Algorithm at VVMC
    Routine Surveillance       Routine Surveillance  
Algo   SSI no SSI Total Algo   SSI no SSI Total
SSI 2 33 35 SSI 0 17 17
no SSI 2 531 533 no SSI 3 832 835
Total 4 564 568 Total 3 849 852
                   
  Sensitivity 50.0%   Sensitivity 0.0%
  Specificity 94.1%   Specificity 98.0%
  Positive Predictive Value 5.7%   Positive Predictive Value 0.0%
  Negative Predictive Value 99.6%   Negative Predictive Value 99.6%

Abbreviations: SSI = surgical site infection; Algo, algorithm

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Table 6. Algorithm Sensitivity (Sn) by Surgical Procedure Type.

  DH IH VA SLCHCS VVMC
  TP FN SN (%) TP FN SN (%) TP FN SN (%) TP FN SN (%)
CABG NA NA NA 4 4 50.0% 0 0 NA 0 0 NA
HERNIA 3 3 50.0% 0 0 NA 1 0 100.0% 0 1 0.0%
HIP 1 3 25.0% 3 5 37.5% 0 2 0.0% 0 1 0.0%
KNEE 2 1 66.7% 2 7 22.2% 1 0 100.0% 0 1 0.0%
Total 6 7 46.2 4 4 50.0 2 2 50.0 0 3 0.0

Abbreviations: CABG, coronary artery bypass grafting; HERNIA, herniorraphy; HIP, total hip arthroplasty; KNEE, total knee arthroplasty; NA, not applicable; TP, true positives; FN, false negatives; Sn, sensitivity

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Table 7. Accuracy of Adjudicated Algorithm at Each Participating Hospital

Accuracy of Adjudication at DH Accuracy of Adjudication at IH
    Routine Surveillance       Routine Surveillance  
Adjudicated   SSI no SSI Total Adjudicated   SSI no SSI Total
SSI 6 1.42 7.42 SSI 9 0 713
no SSI 3 1410 1348 no SSI 16 11559 11575
Total 9 1411.4 1420.4 Total 25 11559 11584
                   
  Sensitivity 66.7%   Sensitivity 36.0%
  Specificity 99.9%   Specificity 100.0%
  Positive Predictive Value 80.9%   Positive Predictive Value 100.0%
  Negative Predictive Value 99.8%   Negative Predictive Value 99.9%
Accuracy of Adjudication at VA SLCHCS Accuracy of Adjudication at VVMC
    Routine Surveillance       Routine Surveillance  
Adjudicated   SSI no SSI Total Adjudicated   No Change  
SSI 2 4 35        
no SSI 2 560 562        
Total 4 564 568        
                   
  Sensitivity 50.0%      
  Specificity 99.3%      
  Positive Predictive Value 33.37%      
  Negative Predictive Value 99.6%      

This table also removes surgeries that were considered invalid after manual review.

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Page last reviewed December 2012
Internet Citation: Appendix V. JAMIA Draft Manuscript Tables. December 2012. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/research/findings/final-reports/ssi/ssiapvtables.html