Dependence of Xpert MTB/RIF Accuracy for Detecting Rifampin Resistance in Bronchoalveolar Lavage Fluid on Bacterial Load: A Retrospective Study in Beijing, China

Figures & data

Figure 1 Enrolment of participants in this study.

Abbreviations: RIF, rifampicin; R, resistant; S, susceptible.

Table 1 Diagnostic Accuracy of Xpert MTB/RIF Assay Stratified to Bacterial Load

Bacterial Load	Xpert MTB/RIF	DST		Total	Sensitivity (%, 95% CI)	Specificity (%, 95% CI)	PPV (%, 95% CI)	NPV (%, 95% CI)
		R	S
High	R	12	1	13	100.0 (100.0–100.0)	97.4 (92.5–100.0)	92.3 (77.8–100.0)	100.0 (100.0–100.0)
	S	0	38	38
	Total	12	39	51
Medium	R	37	4	41	100.0 (100.0–100.0)	98.0 (96.1–99.9)	90.2 (81.2–99.3)	100.0 (100.0–100.0)
	S	0	198	198
	Total	37	202	239
Low	R	54	5	59	98.2 (94.7–100.0)	98.0 (96.3–99.7)	91.5 (84.4–98.6)	99.6 (98.8–100.0)
	S	1	247	248
	Total	55	252	307
Very low	R	47	23	70	90.4 (82.4–98.4)	85.9 (80.5–91.2)	67.1 (56.1–78.1)	96.6 (93.6–99.5)
	S	5	140	145
	Total	52	163	215

Notes: The bolded number represents the BALF samples with very low bacterial load has a significantly PPV compared with other groups.

Abbreviations: DST, drug susceptibility testing; R, resistant; S, susceptible; PPV, positive predict value; NPV, negative predict value; CI, confidential interval.

Table 2 Sequence Analysis of Cases Detected by Xpert MTB/RIF in BALF Samples with Very Low Bacterial Load

Mutation Detected by Xpert MTB/RIF (n=70)	Sequencing Results	Percentage of Isolates with RRDR Mutations^a
Non-Probe E (n=9)	Leu511Pro (n=1)	100.0%
	Gln513Pro(n=1)
	Asp516Val(n=2)
	His526Leu(n=1)
	His526Tyr(n=4)
Probe E (n=61)	Ser531Leu (n=41)	67.2%
	Wild-type (n=20)^b

Notes: ^aRRDR, rifampin resistance determining region. ^bOf 23 false-positive cases, 20 (87.0%) had no mutation within RRDR, 1 had Leu511Pro, 1 had His526Tyr, and 1 had Ser531Leu substitution.