Smear-positive and culture-negative results of routine sputum investigations for the detection and therapy control of pulmonary tuberculosis.

The frequency of smear-positive and culture-negative results (M + C-) is an important factor in the supervision by the Central Laboratory of its own activities and those of the laboratories in the periphery. Under the conditions of the present study, which included evaluation of 6415 specimens positive on smear during 5 years and studied simultaneously by microscopy and culture, about one half of the M+C- results (3% of the total) were thought to be probably laboratory errors and the other half were from patients being treated by chemotherapy. It is necessary to know, at least approximately, the size of this latter group of persons before the contribution of laboratory errors can be estimated and the necessary action taken to reduce their frequency.