ASSESSMENT OF THE MICROSCOPIC– OBSERVATION- DRUG - SUSCEPTIBLITY ASSAY (MODS) AND GENEXPERT ASSAY FOR DIAGNOSIS OF PULMONARY TUBERCULOSIS

Abstract

Background: Tuberculosis (TB) is considered the most common and highly contagious disease worldwide. Early and accurate diagnosis of TB with detection of multidrug-resistant Mycobacterium tuberculosis (M.TB) is of primary importance for both patient management and infection control. Objectives: To evaluate the performance of Microscopic-Observation Drug-Susceptibility (MODS) assay and GeneXpert MTB/RIF( GeneXpert ) assay in diagnosis of TB and detection of MDR-TB directly from sputum specimens in comparison to the convential diagnostic methods (direct Ziehl-Neelsen "Z-N" stained smear and culture on Lowenstein-Jenson media "LJ"). Patients and Methods: After approval of institutional ethical committee a total of 120 suspected pulmonary TB patients admitted to chest hospitals and dispensaries in Egypt (Giza, Cairo, Alexandria, Dakahlia, Suez, Beheira, Monufia, Qena). Their age was more than 16 years; all of them did not receive any anti tubercular drugs. Sputum samples were collected from each patient and subjected to direct ZN smear, culture and sensitivity of M.TB on LJ and Middlebrook 7H9 medium for MODS assay. Finally Genexpert M.TB/RIF assay was done directly for all sputum samples. Results: Infection rate among males was higher than female (81.7% & 18.7%). Also, it was observed that 56.7% of sputum samples gave positive direct Z-N smear, while 64.2% were positive for both LJ culture &MODS assay. On the other hand, by Genexpert, 68% of cases were positive. The sensitivity and specificity of the various diagnostic methods were studied in relation to LJ culture (gold standard). It was found that MODS assay was rapid that results were obtained in a median of 8 days ranged from (7– 21 days), while median time of LJ was 21dayes ranged from (21– 60). MODS had 100% sensitivity and specificity. Direct smear was less sensitive (88.3%), and GeneXpert was less specific (88.4%), but more rapid results were obtained in 2 hours. Finally, detection of MDR-TB using various methods for 77 isolated M.TB strains ranged from 16.9-19.5% to isoniazid (INH) and 9.8%-18.2% to rifampicin (RMP) by various diagnostic methods with statistically insignificant difference between them. Conclusion: MODS was an optimal alternative rapid diagnostic technique for TB and detection of M.TB and MDR-TB in resource limited settings, results were obtained in a median of 8 days. On the other hand, Gene Xpert was a novel integrated diagnostic PCR analysis in a single hand free step for rapid diagnosis of TB and detection of RMP resistance in clinical specimens in 2 hours but it was expensive.