Some operational factors influencing the utility of culture examination in the diagnosis of pulmonary tuberculosis.

Culture examination is technically superior to direct microscopy in the diagnosis of pulmonary tuberculosis, but its practicability and relative importance in various phases of national tuberculosis control programmes in developing countries must be studied before culture facilities are provided on a large scale.Some operational factors affecting the efficacy of the culture method have been analysed in four studies conducted by the National Tuberculosis Institute, Bangalore. The results showed that an interval of up to 7 days between collection of specimens in the field and culture in the laboratory did not affect the yield of positive cultures, even though the specimens were stored and transported under field conditions. A higher proportion of positive cases was detected by culture than by direct microscopy, but the magnitude of the additional yield was dependent upon the procedure for selecting persons for sputum examination. In service programmes restricted to persons with symptoms who voluntarily attend diagnostic centres, the increased yield is too small to justify the introduction of culture examination. The method is substantially rewarding, however, in the evaluation of national control programmes, in changes of drug regimen consequent on altered bacteriological status, and in mass programmes for the early detection of infectious cases.