Incidence and Patterns of Drug Resistance in Patients with Spinal Tuberculosis: a Prospective, Single-Center Study from a Tuberculosis-Endemic Country.

Background: There is paucity of data on incidence and pattern of drug resistance in spinal TB. This prospective observational study was conducted to document the incidence and drug-resistance pattern among primary and presumptive resistant cases.

Methods: 59 consecutive cases diagnosed clinico-radiologically (imaging) were grouped into Group A ( = 51, primary cases) and Group B ( = 8, presumptive resistant cases) based on pre-defined criteria (INDEX-TB guidelines). Tissue samples obtained percutaneously (37.29%, 22/59) and on surgery (62.71%, 37/59) were subjected to genotypic DST (CBNAAT, LPA) and phenotypic DST (BACTEC MGIT 960 culture and sensitivity using fixed critical concentration of drugs).

Results: Etiological diagnosis was ascertained in all. 13/51 (25.49%) in Group A, while 3/8 (37.5%) in Group B and 16/59 (27.12%) overall demonstrated drug resistance. 12/16 (75%) had no prior history of ATT intake. 4 demonstrated INH (Isoniazid) mono-resistance. 12 polydrug resistance demonstrated: 5MDR, 3pre-XDR, while RIF + FQ (fluoroquinolones), FQ + Lz (linezolid), only SLID (second-line injectable drugs), and only FQ resistance observed in 1 case each. Isolated RIF (Rifampicin) resistance and XDR pattern were not observed. Overall frequency of RIF resistance was 16.4% (9/55) and INH was 25% (12/48) with low-(-2) and high-level INH resistance (-10). Among second-line drugs, FQ resistance was more than SLID resistance and within FQ, levofloxacin resistance was more frequent than moxifloxacin. MGIT demonstrated positive growth in 16/59 samples, out of which 1 sample was positive for nontuberculous mycobacteria () but on genotypic testing demonstrated MTB resistant to RIF and FQ.

Conclusion: This is the first report on incidence and drug-resistant pattern in culture-positive/negative cases. High (25.49%) primary drug resistance is worrisome. This being the first study in  spinal TB cases which document prevalent drug-resistant pattern as evaluated for consecutive culture-positive/negative cases. The tissue obtained must be submitted for AFB culture and molecular tests to ascertain drug resistance in culture-positive/negative cases. However, in the presence of insufficient tissue sample histology and CBNAAT can ascertain etiological diagnosis in 100% cases. INH resistance is more than RIF with isolated RIF resistance unreported.