Some aspects of laboratory investigations in a mass campaign against tuberculosis.

In a study of some of the difficulties attending the bacteriological examination of sputa in mass campaigns against tuberculosis, the authors show that culture of specimens always yields significantly more positive results than routine microscopy alone and that sputum culture is more efficient than laryngeal-swab culture. The effect and occurrence of contamination in cultures were investigated in a special trial, and it was found that even minimal contamination adversely affects mycobacterial growth and is sufficient grounds for discarding contaminated cultures. Because of the anticipated detrimental effect of transporting specimens, a subsidiary trial was made to determine whether it would be possible to inoculate cultures in the field for subsequent examination in the laboratory; despite the high contamination rates to be expected from cultures prepared in the field, the technique might prove useful for supplementing microscopic examination in rural centres, since the positivity rate among uncontaminated cultures is not affected. It is also shown that nearly as much information may be obtained from three cultures prepared from each of two sputum specimens as from a third specimen, and at much less cost and effort.