Detection of Mycobacterium tuberculosis by rapid molecular methods augments acid fast bacilli (AFB) smear microscopy in a non-culture tuberculosis laboratory

Laboratory diagnosis of tuberculosis (TB) has evolved into simplified molecular procedures that are adaptable in routine settings. We compared the diagnostic performance of smear microscopy by Ziehl-Neelsen (ZN) for detection of acid fast bacilli (AFB) with two different rapid Mycobacterium tuberculosis (MTB) specific molecular methods; Xpert MTB/RIF (Xpert) and Geno Type MTBDRplus (MTBDR), using a total of 194 consecutive sputum specimens from cases of pulmonary tuberculosis (PTB) in Jos, Nigeria. AFB was detected in 20% of cases by SM; while MTB was detected in 21 and 24% cases by Xpert and MTBDR, respectively. Fifty two (27%) of 194 specimens tested, were positive for AFB, MTB or both. One of 52 (2.0%) AFB positive result was MTB negative while 11/52 (21%) MTB positive cases were AFB negative. There was concordance in 65% of positive results detected by the three methods. MTB drug resistance by the molecular methods occurred in 26 MTB positive cases, of which 8/26 (31%) were MDR-TB. The simultaneous detection of MTB and the associated drug resistance, using Xpert and MTBDR improved TB diagnosis in Jos, Nigeria. We suggest the use of parallel testing of sputum specimens by SM and Xpert, with the retesting of rifampicin (RIF) resistant presumptive MDR-TB cases by MTBDR, as algorithm for TB diagnosis in high TB burden countries with limited TB culture laboratories.