Infectivity of secondary dapsone-resistant cases.

The incidence rate of leprosy among 517 household contacts of 113 cases of secondary dapsone resistance with 5074 person years at risk were studied. The incidence rate of leprosy was 4.3 per 1000 person years at risk, which is very similar to the incidence rate (4.8) among household contacts of lepromatous cases. Two, possibly three, cases of primary dapsone resistance were detected among the 27 contacts who developed multibacillary leprosy. There was no evidence of dapsone resistance among 48 paucibacillary leprosy cases assessed when treated with dapsone monotherapy. The possibility that secondary dapsone-resistant cases will infect and will result in an increase in the number of primary dapsone-resistant cases needs to be investigated further.