Detection of mycobacteria in patients with pulmonary tuberculosis undergoing chemotherapy using MGIT and egg-based solid medium culture systems

SETTING: National Minami-Yokohama Hospital, Kanagawa, Japan. OBJECTIVE: To compare the performance of a liquid medium system using the Mycobacteria Growth Indicator Tube (MGIT) with that of the conventional Japanese culture system using egg-based Ogawa medium, equivalent to Löwenstein-Jensen medium, in cases with pulmonary tuberculosis on chemotherapy. DESIGN: A single-centre prospective case study of 61 hospitalised patients from 1 May to 31 July 1998 on a standard 6-month regimen of anti-tuberculosis chemotherapy including isoniazid, rifampin, streptomycin or ethambutol, and pyrazinamide. Sputum cultures using both culture systems were performed bi-weekly up to week 16 of treatment, and were further monitored by MGIT alone at the end of chemotherapy and every 6 months after the end of chemotherapy up to 2 years. RESULTS: The detection time by MGIT gradually became longer with the progression of chemotherapy. The recovery rate at weeks 2, 4, 6, 8, and 10 by MGIT were significantly higher (P < 0.05) than on the Ogawa slants. Although one case was microbiologically diagnosed as a relapse, using the more sensitive MGIT system did not increase the relapse rate. CONCLUSION: The gradual prolongation of detection time with the progression of treatment and an attainment of negativity of sputum culture at 4 months after chemotherapy could be a useful intermediate marker to monitor the efficacy of treatment for patients with pulmonary tuberculosis by the MGIT system. Further evaluation is necessary to establish the utility of MGIT in monitoring the treatment process.