Improvement of tuberculosis diagnosis by the Mycobacteria Growth Indicator Tube (MGIT) in a developing country laboratory

In order to improve tuberculosis diagnosis in a developing country (Senegal), we evaluated a new liquid-based medium and nonradioactive system, Mycobacteria Growth Indicator Tube (MGIT), with individual clinical specimens collected in Dakar. The main purpose was to compare the time to detection and the rate of recovery of Mycobacterium tuberculosis complex and to determine its importance with respect to Lowenstein-Jensen (LJ), a liquid-based-medium for isolation of M. tuberculosis complex. 531 specimens were processed with Mycoprep kit containing NaOH-N-acetyl L-cystein and inoculated on both LJ and MGIT and incubated at 37 degrees C for 60 days. For each medium, the recovery rate and the time to detection were recorded. Among the 531 specimens, of which 121 smears were positive, 32.5% (173/531) grew the M. tuberculosis complex. Of these, 103 were smear positive (S+) and 70 smear negative (S-). LJ recovered 54.9% (95/173) and MGIT recovered 91.9% (159/173). Disagreements were observed with 92 isolates, LJ failed to recover 78 while MGIT failed to recover 14. The overall mean time to detection was 20.1 days for LJ and 10.5 days for MGIT. MGIT has shown a better sensitivity in isolation with significant reduction in reporting culture for M. tuberculosis complex. As a simple and a nonradiometric system, it could be used in conjunction with egg-based media in developing countries laboratories.