Detection of Mycobacterium tuberculosis in paucibacillary sputum: performances of the Xpert MTB/RIF ultra compared to the Xpert MTB/RIF, and IS6110 PCR

Diagn Microbiol Infect Dis. 2019 Aug;94(4):365-370. doi: 10.1016/j.diagmicrobio.2019.02.008. Epub 2019 Feb 21.


The Xpert MTB/RIF Ultra assay has recently been launched to improve the detection of smear negative disease. This retrospective study compares the sensitivity of Xpert MTB/RIF Ultra with that of Xpert MTB/RIF tests and IS6110 real-time PCR in sputum. Diagnostic performance of three molecular tests was evaluated using 48 culture-positive clinical respiratory specimens diluted to obtain paucibacillary sputum specimens. Xpert MTB/RIF Ultra had the highest sensitivity of 100% compared to 42% (P < 0.001) for Xpert MTB/RIF and 64.5% (P = 0.02) for IS6110-PCR. All "very low" or "low" positive specimens using Xpert MTB/RIF Ultra were tested positive using IS6110-PCR, but 35.4% were found negative using Xpert MTB/RIF. Xpert MTB/RIF Ultra is more sensitive than the two other tests for sputum with a low bacterial load. Adding detection of IS6110 and IS1081 to rpoB, is a key evolution of the assay and improves the detection of Mycobacterium tuberculosis' DNA in paucibacillary sputum.

Keywords: Chelex®; IS6110-PCR; Mycobacterium tuberculosis; Paucibacillary sputum; Xpert MTB/RIF; Xpert MTB/RIF ultra.

Publication types

  • Comparative Study
  • Evaluation Study

MeSH terms

  • Bacterial Load
  • Bacterial Proteins / genetics
  • Molecular Diagnostic Techniques / standards*
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / isolation & purification*
  • Reagent Kits, Diagnostic / standards*
  • Retrospective Studies
  • Sensitivity and Specificity
  • Sputum / microbiology*
  • Tuberculosis / diagnosis*
  • Tuberculosis / microbiology


  • Bacterial Proteins
  • Reagent Kits, Diagnostic