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.

Costs and cost-effectiveness of tuberculosis cultures using solid and liquid media in a developing country.

SETTING: The expansion of culture has been proposed to aid tuberculosis (TB) control in developing countries. OBJECTIVES: To examine the cost and cost-effectiveness at the Zambian National TB Reference Laboratory of homemade and commercially produced Löwenstein-Jensen culture (HLJ and CLJ) as well as automated and manually read liquid culture (AMGIT and MMGIT). DESIGN: Costs were estimated from the provider's perspective and based on the average monthly throughput. Cost-effectiveness estimates were based on yield during the study period. RESULTS: All techniques show comparable costs per culture (between US$28 and $32). Costs per Mycobacterium tuberculosis specimen detected were respectively US$197, $202, $312 and $340 for MMGIT, AMGIT, CLJ and HLJ. When modelled for the maximum throughput, costs were above US$95 per M. tuberculosis specimen detected for all techniques. When only performed among smear-negative specimens, costs per additionally identified M. tuberculosis would be US$487 for MMGIT and higher for other methods. CONCLUSION: Based on cost-effectiveness grounds, liquid media compare well with conventional solid media, especially where yield of MGIT is substantially higher than that of LJ media. The results indicate high overall costs per culture; the expansion of culture to decentralised levels with lower throughputs may result in even higher costs.