TABLE 2.
Detection of toxigenic C. difficile by cytotoxin, GDH-Q EIA, and sequential algorithms compared with gold standard (cytotoxin assay and PCR)
| Assaya | Result | Comparison to CYT and DPCR resultsb |
|||||
|---|---|---|---|---|---|---|---|
| No. of specimens |
% Sensitivity (95% CI) | % Specificity (95% CI) | % PPV (95% CI) | % NPV (95% CI) | |||
| Either positivec | Negative | ||||||
| CYT (tissue culture) | Positive | 47 | 0 | 58.8 | 100 | 100 | 94.9 |
| Negative | 33 | 619 | (47.8-68.9) | (93.0-96.4) | |||
| GDH-Q | Positive | 69 | 45 | 86.3 | 92.7 | 60.5 | 98.1 |
| Negative | 11 | 574 | (76.9-92.3) | (90.4-94.5) | (51.3-69.0) | (96.6-99.0) | |
| Two-step GDH-Q/AB-Q | Positive | 26 | 2d | 32.5 | 99.7 | 92.9 | 92.0 |
| Negative | 54 | 617 | (23.2-43.4) | (98.8-100) | (76.3-99.1) | (89.6-93.8) | |
| Three-step GDH-Q/AB-Q/DPCR | Positive | 67 | 2d | 83.8 | 99.7 | 97.1 | 97.9 |
| Negative | 13 | 617 | (74.0-90.4) | (98.8-100) | (89.4-99.8) | (96.5-98.8) | |
a
Abbreviations: AB-Q, Tox A/B Quik Chek EIA; GDH-Q, C Diff Quik Chek EIA; DPCR, direct real-time PCR; CI, confidence interval.
b
GDH-Q was performed on all specimens, with AB-Q EIA performed on GDH-Q-positives and DPCR on indeterminate (GDH-Q-positive, AB-Q-negative) specimens.
c
GDH-Q-negative specimens were not tested by DPCR in this study, so the rate of DPCR positivity (1.9%) in 211 GDH-Q-negative, CYT-negative specimens from a subsequent time period was applied to 585 GDH-Q negatives, resulting in 11 specimens designated as GDH-Q negative, DPCR positive.
d
CYT negative and DPCR not done.