Evaluation of a simplified IS6110 PCR for the rapid diagnosis of Mycobacterium tuberculosis in an area with high tuberculosis incidence.

PURPOSE: To assess the diagnostic yield of a simplified IS6110-PCR in an area with high tuberculosis incidence. METHODS: Pulmonary (218) and extrapulmonary (121) samples were collected from 236 patients including smearpositive leprosy patients. All samples were processed to detect acidfast bacilli by microscopy, culture on solid media and PCR. To remove PCR inhibitors, three washing steps of the decontaminated pellet were included before mycobacterial cell lysis by heat treatment. No detergents, enzymes, or chelating agents were used. From the 339 samples, 34 were selected basing on their large volume and were tested by the commercial kit GenoType Mycobacteria Direct (GTMD) (VER 4, Hain Lifescience, Germany) in addition to the tests cited above. RESULTS: The overall sensitivity and specificity of PCR were 93.8 and 98.6% for pulmonary samples, 63.6 and 100% for extrapulmonary samples, respectively. The assay detected MTC in 94.2% of smear positive samples with a positive predictive value of 100%. No inhibition was found among seven samples that were PCR negative but bacteriological confirmed as containing Mycobacterium tuberculosis. No false positive result occurred with samples from leprosy patients. The sensitivities for PCR and GTMD were 81.8 and 75%, respectively. CONCLUSION: PCR could efficiently complement conventional bacteriological tools for the rapid diagnosis of tuberculosis but cannot replace them.

Rapid detection of immunoglobulin G against Mycobacterium tuberculosis antigens by two commercial ELISA kits.

SETTING: Tunisia. OBJECTIVE: To assess the clinical usefulness of the commercial Pathozyme-Myco G (Myco G) and Pathozyme TB complex plus (Patho) enzyme-linked immunosorbent assay (ELISA) kits for the rapid diagnosis of active tuberculosis (TB) and to distinguish between active TB and non-TB pulmonary diseases in Tunisian patients. DESIGN: Immunoglobulin G mediated humoral immune response against mycobacterial antigens (38 kDa and lipoarabinomannan, Myco G; 16 and 38 kDa, Patho) was evaluated in a group of active TB patients (128 smear-positive pulmonary and 33 extra-pulmonary samples) and in a control group (107 patients with non-tuberculous lung disease and two with leprosy). Active TB cases were confirmed by Mycobacterium tuberculosis culture from clinical samples. RESULTS: The sensitivity of the Myco G test was 71% in active TB (pulmonary and extra-pulmonary), while the specificity was 100%. The Patho test showed a sensitivity of 43.5% with a specificity of 96.3%. A combination of both tests showed a sensitivity of 81% and a specificity of 96.3%. CONCLUSIONS: Both ELISA tests were simple and easy to perform. Their combined use led to an increase in the diagnostic accuracy of active TB and its discrimination from non-TB pulmonary diseases. They could therefore be used as screening tools in poorly equipped laboratories in TB-endemic regions.