Performance of the G4 Xpert® MTB/RIF assay for the detection of Mycobacterium tuberculosis and rifampin resistance: a retrospective case-control study of analytical and clinical samples from high- and low-tuberculosis prevalence settings

Table 3 Xpert MTB/RIF Assay performance vs. MTB culture stratified by specimen collection method and specimen type

	AFB Smear-positive subjects	AFB Smear-negative subjects	All samples
Specimen Collection Method^a
Expectorated Sputum (n = 535)
Sensitivity	99.6% (271/272)^b	79.0% (75/95)^c	94.3% (346/367)^d
Sensitivity	95% CI: 97.9 – 99.9%	95% CI: 69.7 – 85.9%	95% CI: 91.4 – 96.2%
Specificity			97.6% (164/168)^b
Specificity			95% CI: 94.0 – 99.1%
Induced Sputum (n = 234)
Sensitivity	100% (15/15)^b	40.0% (4/10)^c	76% (19/25)^d
Sensitivity	95% CI: 79.6 – 100%	95% CI: 16.8 – 68.7%	95% CI: 56.6 – 85.5%
Specificity			99.0% (207/209)^b
Specificity			95% CI: 96.6 – 99.7%
Specimen Type
Raw Sputum (n = 606)
Sensitivity	99.7% (285/286)^b	79.4% (77/97)^e	94.5% (362/383)^b
Sensitivity	95% CI: 98.0 – 99.9%	95% CI: 70.3 – 86.2%	95% CI: 91.8% - 96.4%
Specificity			97.8% (218/223)^b
Specificity			95% CI: 94.9 – 99.0%
Concentrated Sputum Sediment (n = 490)
Sensitivity	100% (65/65)^b	60.0% (12/20)^e	90.6% (77/85)^b
Sensitivity	95% CI: 94.4 – 100%	95% CI: 38.7 – 78.1%	95% CI: 82.5% - 95.2%
Specificity			99.3% (402/405)^b
Specificity			95% CI: 97.8 – 99.7%

ISSN: 1471-2334