Liquid vs. solid culture for tuberculosis: performance and cost in a resource-constrained setting.
METHODS
National Health Laboratory Services tuberculosis (TB) laboratory, South Africa.


OBJECTIVE
To compare Mycobacterium Growth Indicator Tube (MGIT) with Löwenstein-Jensen (LJ) medium with regard to Mycobacterium tuberculosis yield, time to positive culture and contamination, and to assess MGIT cost-effectiveness.


METHODS
Sputum from gold miners was cultured on MGIT and LJ. We estimated cost per culture, and, for smear-negative samples, incremental cost per additional M. tuberculosis gained with MGIT using a decision-tree model.


RESULTS
Among 1267 specimens, MGIT vs. LJ gave a higher yield of mycobacteria (29.7% vs. 22.8%), higher contamination (16.7% vs. 9.3%) and shorter time to positive culture (median 14 vs. 25 days for smear-negative specimens). Among smear-negative samples that were culture-positive on MGIT but negative/contaminated on LJ, 77.3% were non-tuberculous mycobacteria (NTM). Cost per culture on LJ, MGIT and MGIT+LJ was respectively US$12.35, US$16.62 and US$19.29. The incremental cost per additional M. tuberculosis identified by standard biochemical tests and microscopic cording was respectively US$504.08 and US$328.10 using MGIT vs. LJ, or US$160.80 and US$$109.07 using MGIT+LJ vs. LJ alone.


CONCLUSIONS
MGIT gives higher yield and faster results at relatively high cost. The high proportion of NTM underscores the need for rapid speciation tests. Minimising contaminated cultures is key to cost-effectiveness.
Chihota
V N
VN
Aurum Institute for Health Research, Johannesburg, South Africa. vchihota@auruminstitute.org
Grant
A D
AD
Fielding
K
K
Ndibongo
B
B
van Zyl
A
A
Muirhead
D
D
Churchyard
G J
GJ
D000328:Adult; D000368:Aged; D001431:Bacteriological Techniques / Q000191:economics* / Q000592:standards*; D003365:Costs and Cost Analysis; D003470:Culture Media / Q000191:economics / Q000592:standards*; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D019907:Mycobacterium fortuitum / Q000254:growth & development / Q000302:isolation & purification*; D015995:Prevalence; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013019:South Africa / Q000453:epidemiology; D013183:Sputum / Q000382:microbiology*; D014376:Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D055815:Young Adult
D003470:Culture Media