Diagnostic Accuracy of Ziehl-Neelsen Smear Microscopy in Comparison with GeneXpert in Pulmonary Tuberculosis: A Multi-Center Study in Kandahar Province, Afghanistan

Background: Tuberculosis (TB) is a major global health problem. The early and accurate diagnosis is crucial for disease management and to control disease transmission and the emergence of drug resistance TB.

Objectives: This study was carried out to determine the diagnostic accuracy of Ziehl Neelsen (ZN) smear microscopy in comparison with GeneXpert MTB/RIF in pulmonary tuberculosis in Kandahar province, Afghanistan.

Methods: This was a facility-based cross-sectional study. We scrutinized TB registers of three health facilities to include patients who had their sputum tested by both ZN smear microscopy and GeneXpert MTB/RIF. We extracted 734 patients’ data registered during January 2019 - June 2020 in a structured form. Kappa value was analyzed using SPSS version 19 software at 95% Confidence Interval (CI). We calculated sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of ZN smear microscopy against GeneXpert MTB/RIF.

Results: In comparison with GeneXpert as a reference test, ZN smear microscopy has 67.7% (95% CI:63.44%-70.74%) sensitivity and 100% (95% CI:98.74%-100.00%) specificity. The positive predictive value (PPV) and negative predictive value (NPV) were 100% and 99.89% (95% CI:99.88%-99.90%), respectively. The agreement between ZN smear microscopy and GeneXpert MTB/RIF results was moderate (70.4%) and the Kappa value was 0.45 (95% CI:0.38-0.59).

Conclusion: This study has found high specificity but moderate sensitivity for the diagnosis of pulmonary TB using sputum ZN smear microscopy test. Hence, GeneXpert MTB/RIF test is more accurate and reliable for the diagnosis of pulmonary TB.