Comparison of four culture systems for Mycobacterium tuberculosis in the Zambian National Reference Laboratory.

SETTING: National TB Reference Laboratory, Zambia. OBJECTIVE: To compare four TB culture systems when used in a resource-limited setting. DESIGN: Comparison of four culture systems: automated Mycobacterium Growth Indicator Tube (AMGIT) 960, manual MGIT (MMGIT) and two Löwenstein-Jensen (LJ) culture media-commercial (CLJ) and homemade (HLJ). RESULTS: A total of 1916 sputum specimens were received, of which 261 (13.6%) were positive on microscopy. Mycobacterium tuberculosis complex (MTC) was isolated on at least one of the media in 410 (21.4%) specimens: MMGIT recovered 336 (17.5%) MTC, AMGIT 329 (17.2%), CLJ 192 (10.0%) and HLJ 184 (9.6%). The median time to detection for smear-negative specimens was 14 days for AMGIT, 16 days for MMGIT and 34 days for both LJ. Isolation of non-tuberculous mycobacteria (NTM) was more frequent in both MGIT systems (3.5%) than in CLJ (0.9%) and HLJ (0.8%). Contamination rates were high: 29.6% on AMGIT, 23.8% on MMGIT, 14.9% on CLJ and 12.5% on HLJ. CONCLUSION: Despite high contamination rates, either MGIT system considerably improved both the yield and the time to detection of MTC compared to LJ media. Investments in infrastructure and training are needed if culture is to be scaled up in low-income settings such as this.