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
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
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
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.
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
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
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.
