Accuracy of Xpert® MTB/RIF Ultra test for posterior oropharyngeal saliva for the diagnosis of paucibacillary pulmonary tuberculosis: a prospective multicenter study

Figures & data

Figure 1. Trial profile. X-Ultra = Xpert MTB/RIF Ultra; X-Classic = Xpert MTB/RIF; MGIT = mycobacteria growth indicator tube; POS = posterior oropharyngeal saliva.

Table 1. Baseline characteristics of participants who underwent pulmonary tuberculosis testing.

	Pulmonary tuberculosis (N = 345)	Other pulmonary diseases (N = 299)	p value
Age, year	36.0 (28.0–55.0)	58.0 (48.0–68.0)	<0.001
≤44	214 (62.0)	59 (19.7)
45–59	70 (20.3)	102 (34.1)
≥60	61 (17.7)	138 (46.2)
Sex			0.225
Female	156 (45.2)	121 (40.5)
Male	189 (54.8)	178 (59.5)
Ethnicity			0.515
Han	334 (96.8)	292 (97.7)
Minority	11 (3.2)	7 (2.3)
Previous TB episode	99 (28.7)	23 (7.7)	<0.001
Smoke history	76 (22.0)	100 (33.4)	0.001
Comorbidities
COPD	3 (0.9)	32 (10.7)	<0.001
Bronchiectasia	8 (2.3)	22 (7.4)	0.002
Asthma	2 (0.6)	9 (3.0)	0.018
Diabetes	38 (11.0)	50 (16.7)	0.035
Hepatitis	12 (3.5)	10 (3.3)	0.926
HIV	1 (0.3)	0 (0.0)	>0.999
Symptom
Cough	244 (70.7)	208 (69.6)	0.748
Hemoptysis	38 (11.0)	34 (11.4)	0.886
Fever	95 (27.5)	53 (17.7)	0.003
Weight loss	38 (11.0)	37 (12.4)	0.592

Figure 2. Venn diagram of overlap in paucibacillary tuberculosis on POS and BALF. X-Ultra = Xpert MTB/RIF Ultra; X-Classic = Xpert MTB/RIF; MGIT = mycobacteria growth indicator tube; POS = posterior oropharyngeal saliva; BALF = bronchoalveolar lavage fluid; AUC = Area Under Curve.

Figure 3. Relative risk of false-negative X-Ultra results on POS samples stratified by bacterial load. X-Ultra = Xpert MTB/RIF Ultra; POS = posterior oropharyngeal saliva; OR = odds ratio. The bacterial load is quantified by X-Ultra assay on BALF specimen.

Table 2. Diagnostic performance of X-Ultra and X-Classic against reference standard.

Methods	BALF X-Classic	BALF X-Ultra	POS X-Classic	POS X-Ultra
Reference standard: definite pulmonary TB
Positive test	166/227	221/227	128/227	179/227
Sensitivity	73.1(66.8–78.7)	97.4(94.1–98.9)	56.4(49.7–62.9)	78.9(72.8–83.8)
Specificity	100.0(98.9–100.0)	100.0(98.9–100.0)	97.6(95.5–98.8)	96.6(94.3–98.1)
PPV	100.0(97.2–100.0)	100.0(97.9–100.0)	92.8(86.7–96.3)	92.7(87.9–95.8)
NPV	87.2(83.8–90.0)	98.6(96.8–99.4)	80.4(76.6–83.7)	89.4(86.0–92.0)
AUC	86.6(83.0–90.1)	98.7(97.5–99.9)	77.0(72.7–81.3)	87.7(84.4–91.1)
Reference standard: definite and clinically diagnosed pulmonary TB
Positive test	166/345	221/345	138/345	193/345
Sensitivity	48.1 (42.8–53.5)	64.1 (58.7–69.1)	40.0 (34.8–45.4)	55.9 (50.5–61.2)
Specificity	100.0 (98.4–100.0)	100.0 (98.4–100)	100.0 (98.4–100.0)	100.0 (98.4–100.0)
PPV	100.0 (97.2–100.0)	100.0 (97.9–100.0)	100.0 (96.6–100.0)	100.0 (97.6–100.0)
NPV	62.6 (58.0–66.9)	70.7 (66.1–75.0)	59.1 (54.7–63.4)	66.3 (61.7–70.6)
AUC	74.1 (70.2–77.9)	82.0 (78.7–85.4)	70.0 (66.0–74.0)	78.0 (74.4–81.6)

Notes: Data in parentheses are 95% CIs. X-Ultra = Xpert MTB/RIF Ultra; X-Classic = Xpert MTB/RIF; PPV = positive predictive value; NPV = negative predictive value.