Application of the Crystal Violet Decolorization Assay for Identification of Mycobacterium tuberculosis in Rural Areas of the Union Territory of Dadra and Nagar Haveli, India

Tuberculosis (TB) remains a significant public health challenge in rural India, where access to advanced diagnostics is limited. The Crystal Violet Decolorization (CVD) assay offers a potential low-cost, microscopy-based alternative for detecting Mycobacterium tuberculosis and drug resistance. The CVD assay was assessed for M. tuberculosis detection against CBNAAT and for rifampicin and isoniazid resistance against CBNAAT and culture-based drug susceptibility testing, respectively. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated, with feasibility assessed via turnaround time and cost. Of 350 samples, CBNAAT identified 82 (23.4%) as M. tuberculosis-positive. The CVD assay demonstrated a sensitivity of 92.68% (95% CI: 84.76-97.30%) and specificity of 98.13% (95% CI: 95.70-99.43%) for TB detection, comparable to ZN staining (sensitivity 89.02%, specificity 97.76%). For drug resistance, the CVD assay achieved sensitivities of 85.71% (95% CI: 57.19-98.22%) for rifampicin and 81.25% (95% CI: 54.35-95.95%) for isoniazid, with specificities of 98.53% and 96.77%, respectively. The assay’s turnaround time was 2.5 hours for TB detection and 26.5 hours for resistance testing, with a cost of INR 150 per test, significantly lower than CBNAAT (INR 2000) and culture (INR 2500). The CVD assay offers high diagnostic accuracy for M. tuberculosis detection and good performance for drug resistance screening, with cost-effectiveness and feasibility for rural settings. The assay’s simplicity and affordability make it a promising tool for enhancing TB control in resource-limited regions, supporting India’s National Strategic Plan for Tuberculosis Elimination.