Comparative Study of Smear Microscopy, Gene Xpert and Culture and Sensitivity Assays in Detection of Mycobacterium tuberculosis on Sputum Samples among Tuberculosis Suspected Cases in Nyamira County Referral Hospital

Abstract

The laboratory diagnosis of pulmonary tuberculosis and smear-negative pulmonary tuberculosis in resourcelimited countries are often based on X-ray and sputum smear microscopy. These diagnostic tools require experts, have long turnaround time, and cannot detect resistance to Tuberculosis (TB) drugs and TB in individuals with Human immunodeficiency virus. Recently there was development of GeneXpert MTB/Rif assay that has a short turnaround time and can detect resistance to rifampicin among TB patients but its utility has not been evaluated in Kenya. This study investigated the comparative sensitivity and specificity of smear microscopy and culture relative to GeneXpert MTB/Rif assay among suspected TB patients. A cross-sectional study was conducted in Nyamira County Referral Hospital among suspected TB patients and both results recorded. Culture for Mycobacterium tuberculosis served as the reference standard. The results of this study showed that among 682 enrolled participants, 182(26.69%) were diagnosed TB positive while 500 (73.31%) no TB. GeneXpert mtb/rif had a higher sensitivity (100%) and specificity (99.4%) relative to culture and a positive predictive value of (98.4%) and a negative predictive value of (100%). Smear microscopy revealed low sensitivity (26.4%) and a higher specificity (98.2%). A concordance analysis of smear microscopy and GeneXpert was done. The findings revealed a significant (patients showed resistance to either one of the TB drugs (rifampicin, isoniazid and Ethambutol) while none of the enrolled patients were resistant to streptomycin. In conclusion Gene Xpert MTB/Rif test had high sensitivity compared to smear microscopy. For rifampicin resistance detection, it provided accurate results. My recommendation to the Division of TB and lung diseases is to roll out the Gene Xpert mtb/rif machines to all health care facilities.