Diagnostic performance of GeneXpert and Ziehl-Neelson microscopy in the detection of tuberculosis in Benue State, Nigeria

Abstract

Background: Accurate and timely diagnosis of tuberculosis (TB) is key to effective treatment and management. This study was designed to compare the diagnostic performance of GeneXpert and Ziehl-Neelson (ZN) microscopy test using culture as the reference.

Methods: Cross-sectional study was conducted in a tertiary hospital to compare the performance of GeneXpert and ZN test among HIV and non-HIV patients. Sputum samples were collected from 261 suspected TB patients and analyzed in the laboratory using GeneXpert, ZN test and culture. Statistical analysis included calculation of sensitivity, specificity, positive predictive value and negative predictive value. X² was used to compare the outcome of diagnostic test and demographic variables. p-value < 0.05 was considered significant.

Results: Comparison of TB prevalence among urban versus rural areas using the three diagnostic tests are: ZN test: 32 (12.3%) vs 16 (6.1%; X² 7.63, P = 0.007); GeneXpert: 63 (16.1%) vs 20 (7.7%, X² 9.01, P = 0.003) and culture: 22 (8.4%) vs 10 (3.8% X² 4.44, P = 0.05). Also, prevalence of TB was significantly (P < 0.05) higher among HIV negative 25 (9.6%) than HIV positive 23 (8.8%) patients. The overall prevalence of rifampicin resistance was 12 (4.60%). Out of 261 sputum samples examined for TB, 48 (18.38%) tested positive by ZN test, 62 (23.76%) by GeneXpert and 32 (12.26%) by culture. Two out of 32 samples that tested positive by culture were negative by GeneXpert. GeneXpert had higher sensitivity (93.75%) than ZN test (50.00%). However, they had equal specificity (86.03%). The sensitivity and specificity of ZN and GeneXpert among HIV patients was 58.33% (95% CI = 29.66–84.83) and 79.31% (95% CI; 69.24–87.26) and 91.67% (95% CI 61.51–99.79) and 80.67 (95% CI; 70.58–88.17) while among HIV negative patients; ZN test and GeneXpert assay had 45.00% (23.05–68.45) and 90.14% (84.04–94.50) and 95.00% (75.13–99.87) and 89.44% (83.13–93.96), respectively.

Conclusion: GeneXpert demonstrated higher level of performance than ZN microscopy. We recommend the use of GeneXpert for diagnosis of TB in Benue State and Nigeria in general for effective treatment and management of tuberculosis.

Keywords: Diagnostic performance, GeneXpert MTB/Rif, Ziehl-Neelson, Tuberculosis, HIV