Epidemiology of first-and second-line anti-tuberculosis drug resistance in new pulmonary tuberculosis cases in Addis Ababa metropolitan area, Ethiopia

Abstract

Background: Conventional wisdom holds that the microbiological detection of Mycobacterium tuberculosis  complex in clinical specimens  via culture and phenotypic drug susceptibility testing allows people to be correctly diagnosed and ensures that an effective treatment  regimen is selected.

Aim: The objective of this study was to provide a description of the drug resistance profiles of first-line and second-line anti-tuberculous  drugs among individuals newly diagnosed with pulmonary tuberculosis in the Addis Ababa metropolitan area, located in Ethiopia.

Methods: A cross-sectional study was conducted between October 2019 and June 2021 on clinically suspected and bacteriologically  confirmed pulmonary tuberculosis cases. The GeneXpert MTB/RIF assay was used to detect Mycobacterium tuberculosis complex and  resistant to rifampicin. Mycobacterial culture and drug susceptibility testing were performed against 15 anti-tuberculosis drugs using the  BD BACTEC™ MGIT™ 960 automated liquid culture system. 

Results: A total of 156 Mycobacterium tuberculosis complex isolates were  successfully recovered. Males account for 53.8 % [84/156]. Overall, 14.1% [22/156] of isolates were resistant to at least one drug, 85.9 %  [134/156] of isolates were pan-susceptible, 7.1% [11/156] of isolates were mono-resistant strains, 5.8% [9/156] of isolates were multidrug- resistant strains, and 3.8% [6/156] of isolates were resistant to all first-line drugs. Interestingly, all isolates were susceptible to all recently  recommended second-line drugs tested. Nevertheless, compared to the reference method, the rate of rifampicin resistance detected  using GeneXpert MTB/RIF assay had a sensitivity, specificity, and accuracy of 100% [95% CI: 66.4 – 100], 94.6 [95% CI: 89.6 – 97.6], and 94.9  [95% CI: 90.2 – 97.8] respectively, with moderate level of agreement at Cohen kappa value of 0.667. 

Conclusion: The rate of MDR-TB in  new pulmonary TB cases remained high, at fivefold the national and nearly twofold the global estimated rate in this study. The rate of  monoresistance was also high and alarming. The rate of resistance against second-line anti-TB drugs was absent and quite encouraging.  The use of GeneXpert MTB/RIF assay alone for the detection of M. tuberculosis introduces 15.7% [34/216] false positivity and 47.1% [8/17]  false rifampicin resistance. Treatment initiation with second-line medications without initial drug susceptibility test results may lead to  erroneous decisions