Quality control in tuberculosis bacteriology. 1. Laboratory studies on isolated positive cultures and the efficiency of direct smear examination.

Sputum specimens unlikely to contain M. tuberculosis or specimens artificially created as methylcellulose/egg solution were autoclaved and distributed in batches together with sputum specimens containing viable M. tuberculosis marked with an unusual drug-sensitivity pattern. These specimens were prepared in 1 East African laboratory, divided into aliquots and examined by direct smear and culture in 3 East African laboratories. Independent batches were also prepared and cultured in London. Scanty colonies of M. tuberculosis, always with the characteristic marker sensitivity pattern, were obtained from a proportion of the autoclaved specimens, ranging from 0% of 825 specimens in London to 1.3% of 2165 specimens in Kampala. Transfer of bacilli from positive to negative specimens could therefore account for some of the isolated positive cultures that occur in clinical trials. The occurrence of transfer seemed to be related more to the quality of the technician than to the detail of the technical methods. The African laboratories could be graded in their overall efficiency in smear and culture examination.