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Original article
Accuracy and impact of Xpert MTB/RIF for the diagnosis of smear-negative or sputum-scarce tuberculosis using bronchoalveolar lavage fluid
  1. Grant Theron1,
  2. Jonny Peter1,
  3. Richard Meldau1,
  4. Hoosain Khalfey1,
  5. Phindile Gina1,
  6. Brian Matinyena1,
  7. Laura Lenders1,
  8. Gregory Calligaro1,
  9. Brian Allwood1,
  10. Gregory Symons1,
  11. Ureshnie Govender1,
  12. Mashiko Setshedi1,
  13. Keertan Dheda1,2
  1. 1Department of Medicine, Lung Infection and Immunity Unit, Division of Pulmonology & UCT Lung Institute, University of Cape Town, Cape Town, Western Cape, South Africa
  2. 2Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, Western Cape, South Africa
  1. Correspondence to Dr Keertan Dheda, Department of Medicine, Lung Infection and Immunity Unit, University of Cape Town, H47 Old Main Building, Groote Schuur Hospital, Observatory, Cape Town, Western Cape 7925, South Africa; keertan.dheda{at}uct.ac.za

Abstract

Rationale The accuracy and impact of new tuberculosis (TB) tests, such as Xpert MTB/RIF, when performed on bronchoalveolar lavage fluid (BALF) obtained from patients with sputum-scarce or smear-negative TB is unclear.

Methods South African patients with suspected pulmonary TB (n=160) who were sputum-scarce or smear-negative underwent bronchoscopy. MTB/RIF was performed on uncentrifuged BALF (1 ml) and/or a resuspended pellet of centrifuged BALF (∼10 ml). Time to TB detection and anti-TB treatment initiation were compared between phase one, when MTB/RIF was performed as a research tool, and phase two, when it was used for patient management.

Results 27 of 154 patients with complete data had culture-confirmed TB. Of these, a significantly lower proportion were detected by smear microscopy compared with MTB/RIF (58%, 95% CI 39% to 75% versus 93%, 77% to 98%; p<0.001). Of the 127 patients who were culture negative, 96% (91% to 98%) were MTB/RIF negative. When phase two was compared with phase one, MTB/RIF reduced the median days to TB detection (29 (18–41) to 0 (0–0); p<0.001). However, more patients initiated empirical therapy (absence of a positive test in those commencing treatment) in phase one versus phase two (79% (11/14) versus 28% (10/25); p=0.026). Consequently, there was no detectable difference in the overall proportion of patients initiating treatment (26% (17/67; 17% to 37%) versus 36% (26/73; 26% to 47%); p=0.196) or the days to treatment initiation (10 (1–49) versus 7 (0–21); p=0.330). BALF centrifugation, HIV coinfection and a second MTB/RIF did not result in detectable changes in accuracy.

Conclusions MTB/RIF detected TB cases more accurately and more rapidly than smear microscopy and significantly reduced the rate of empirical treatment.

  • Tuberculosis
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