From the study in British Columbia and Saskatchewan, the proportion of transmissions attributable to smear-positive and smear-negative cases can be calculated. The figure shows that sputum smear examination is a relatively insensitive tool to identify pulmonary tuberculosis (it identified only about 60 per cent of culture-confirmed cases in this study), but is a very sensitive tool to identify sources of infection.
Sputum smear-positive patients are the major sources of transmission of tubercle bacilli in the community.
Studies with more modern techniques (DNA fingerprinting) have basically confirmed this observation.
