Manual liquid culture on simple Middlebrook 7H9 or MGIT for the diagnosis of smear-negative pulmonary tuberculosis

Objectives: To compare the performance of liquid culture on simple Middlebrook 7H9 to the one of manual mycobacterial growth indicator tube (MGIT) and solid culture on Ogawa for the diagnosis of smear-negative tuberculosis (SN-TB) in a high-burden, resource-constrained setting. Methods: Sputum samples from patients with clinical suspicion of SN-PTB admitted to two-third-level hospitals in Lima between September 2005 and May 2008 were cultured in parallel on simple Middlebrook 7H9, manual MGIT and Ogawa. A case of SN-TB was defined as one with a positive culture in any medium. Results: Among samples from 542 patients, 151 (28%) cases of SN-TB were identified. The sensitivity of Middlebrook 7H9 (0.76, 95% CI 0.69–0.83) was not substantially different from that of MGIT (0.85, 95% CI 0.79–0.91). Ogawa had the lowest sensitivity (0.63, 95% CI 0.55–0.71). The median turnaround time was similar for both liquid media (18 days), and it was shorter than that of Ogawa (30 days). Conclusions: Culture on simple Middlebrook 7H9 performs almost as well as MGIT, at a probably more affordable cost. Further studies on the cost-effectiveness of this overlooked technique should be performed.