Viability of stored sputum specimens for smear microscopy and culture

A laboratory study was performed to determine how long sputum specimens from smear-positive tuberculosis patients can be stored at room temperature or in the refrigerator and retain a positive acid-fast bacilli (AFB) smear or a positive mycobacterial culture. Sputum samples from 30 patients were examined up to 4 weeks and samples from 13 patients examined up to 8 weeks. Provided samples had not dried out, all sputum smears remained AFB positive up to 4 and 8 weeks. In both patient groups, at 4 weeks 37-39% of specimens at room temperature grew mycobacteria compared with 54-67% of specimens stored in the refrigerator. These results have implications for tuberculosis programme policy.