Sputum culture and drug sensitivity testing outcome among X-pert Mycobacterium tuberculosis/rifampicin-positive, rifampicin-resistant sputum: A retrospective study — Not all rifampicin resistance is multi-drug resistant

Abstract

Objective: Rifampicin-resistant (RR) tuberculosis (TB) on X-pert Mycobacterium tuberculosis/rifampicin (MTB/Rif) is assumed to be a surrogate for multi-drug resistant (MDR) TB. Following an RR result, a second specimen was taken for confirmatory culture and drug-susceptibility testing (DST). This study compared the initial diagnostic X-pert MTB/RIF result with the confirmatory DST in a high human immunodeficiency virus (HIV) seroprevalence setting. Design: Records analysing demographics, HIV serostatus, prior TB treatments, and DST results were retrospectively reviewed. Results: Of 604 patients with X-pert MTB/RIF RR, 374 (61.9%) had DST and were included. The mean age was 36.9 years and 82% were HIV infected. Following DST, MDR was confirmed in 49% and Rif mono-resistant (RMR) TB in 36%. Amongst RMR TB, 84% were HIV-infected, and amongst those with CD4 < 50 versus those 50–350 cells/mm3 RMR TB was noted in 51% versus 33%, respectively (P = 0.012). Primary DR was diagnosed in 43% (61% MDR and 33% RMR). Conclusion: Rifampicin resistance detected on a diagnostic X-pert MTB/Rif assay did not always predict MDR. Rifampicin mono-resistance is emerging amongst those with HIV co-infection and low CD4 counts (<50 cells/mm3). Research is needed to reduce the number of drugs and treatment durations for RMR TB.

Keywords

• Multidrug-resistant tuberculosis
• Rifampicin mono-resistant tuberculosis
• HIV