Lepromatous-leprosy patients entering treatment with DDS were followed by repeated biopsies of skin lesions. The bacilli in the specimens were counted, scored for solid staining, and their infectiousness tested by inoculation of mice. Some of the patients were also followed by nasal washings.
The infectiousness for mice decreased in the first 30 days, and was only barely detectable at 30 to 90 days, after which it was not detectable. In the range where it could be determined accurately the proportion of solidly staining bacilli decreased in parallel with the infectiousness.
The number of bacilli in the skin specimens decreased much more slowly during the period of observation (the first 300 to 400 days of treatment). The rate of loss was estimated to average 0.93 log10 units (8.5-fold) per year. As observed previously, the number of bacilli in the nasal washings decreased more rapidly than the number of bacilli in the skin. The infectiousness of the nasal bacilli fell at about the same rate as that of the skin bacilli.