Table 2.
Diagnostic performance of Xpert Ultra and Xpert against clinical reference standard
| Xpert Ultra | Xpert | Ziehl–Neelsen smear | MGIT culture | |
|---|---|---|---|---|
| Reference standard: definite, probable, and possible tuberculous meningitis | ||||
| Positive tests | 25/53* | 21/53 | 77/108 | 45/94 |
| Sensitivity | 47·2% (34·4–60·3) | 39·6% (27·6–53·1) | 71·3% (62·5–79·0) | 47·9% (38·0–57·9) |
| Specificity | 100·0% (92·0–100·0) | 100·0% (92·6–100·0) | 100·0% (96·1–100·0) | 100·0% (95·6–100·0) |
| PPV | 100·0% (86·7–100·0) | 100·0% (84·5–100·0) | 100·0% (95·2–100·0) | 100·0% (92·1–100·0) |
| NPV | 61·1% (49·6–71·5) | 60·0% (49·0–70·0) | 72·2% (67·2–82·1) | 63·2% (54·7–70·9) |
| Reference standard: definite and probable tuberculous meningitis | ||||
| Positive tests | 25/43 | 21/43 | 77/88 | 45/75 |
| Sensitivity | 58·1% (43·3–71·6) | 48·8% (34·6–63·2) | 87·5% (79·0–92·9) | 60·0% (48·7–70·3) |
| Specificity | 100·0% (93·4–100·0) | 100·0% (93·8–100·0) | 100·0% (96·8–100·0) | 100·0% (96·4–100·0) |
| PPV | 100·0% (86·7–100·0) | 100·0% (84·5–100·0) | 100·0% (95·2–100·0) | 100·0% (92·1–100·0) |
| NPV | 75·0% (63·9–83·6) | 72·5% (61·9–81·1) | 91·3% (85·0–95·1) | 77·4% (69·6–83·7) |
| Reference standard: definite tuberculous meningitis | ||||
| Positive tests | 25/42 | 21/38 | 77/82 | 45/73 |
| Sensitivity | 59·5% (44·5–73·0) | 55·3% (39·7–69·9) | 93·9% (86·5–97·4) | 61·6% (50·2–72·0) |
| Specificity | 100·0% (93·5–100·0) | 100·0% (94·3–100·0) | 100·0% (96·3–100·0) | 100·0 (96·5–100·0) |
| PPV | 100·0% (86·7–100·0) | 100·0% (84·5–100·0) | 100·0% (95·2–100·0) | 100·0% (92·1–100.0) |
| NPV | 76·4% (65·4–84·7) | 78·8% (68·6–86·3) | 95·3% (89·4–98·0) | 79·0% (71·3–85·0) |
Data in parentheses are 95% CIs. Xpert Ultra=Xpert MTB/RIF Ultra. Xpert=Xpert MTB/RIF. MGIT=mycobacteria growth indicator tube. PPV=positive predictive value. NPV=negative predictive value.
*
Of 55 cases of definite, probable, or possible tuberculous meningitis tested by Xpert Ultra, two with definite tuberculosis returned an error result. Therefore, only 53 cases are included in the sensitivity calculation. Of the 205 participants enrolled in the study, Ziehl–Neelsen smear and MGIT were done in 204 (>99%) and 187 (91%) cases, respectively.