Table 2.
Impact changes in sensitivity, specificity, and repeat testing on CDI prevalence, positive predictive value, negative predictive value, and perceived CDI burden. All comparisons start with 10,000 inpatients with diarrhea tested for C. difficile. 41% with a negative first test had a second test performed. 53% with a negative second test had a third test performed.
| Test Number | CDI Prevalence | Positive n | Negative n | False Positive n (%) | PPV | NPV |
|---|---|---|---|---|---|---|
| Sensitivity = 90.3%, Specificity = 96.2% | ||||||
| First | 14.9% | 1,669 | 8,331 | 323 (19.4) | 80.6% | 98.3% |
| Second | 1.7% | 181 | 3,232 | 127 (70.2) | 29.6% | 99.8% |
| Third | 0.2% | 68 | 1,719 | 65 (95.6) | 4.1% | 100.0% |
| Sensitivity = 75%, Specificity = 96.2% | ||||||
| First | 14.9% | 1,441 | 8559 | 323 (22.4) | 77.6% | 95.6% |
| Second | 4.4% | 242 | 3265 | 127 (52.5) | 47.3% | 98.8% |
| Third | 1.2% | 80 | 1655 | 65 (81.3) | 18.9% | 99.7% |
| Sensitivity = 90.3%, Specificity = 95.0% | ||||||
| First | 14.9% | 1,771 | 8,229 | 426 (24.1) | 76.0% | 98.2% |
| Second | 1.8% | 219 | 3,371 | 166 (75.8) | 24.4% | 99.8% |
| Third | 0.2% | 87 | 1,676 | 84 (97.7) | 3.2% | 100.0% |
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CDI = C. difficile infection, PPV = positive predictive value, NPV = negative predictive value