Incidence rates of leprosy among household contacts of "primary cases".

The data consisted of information from 1,564 "Primary cases" of leprosy of all classification and 9,162 of their household contacts. Household contacts of Indeterminate (Ind), Borderline (BL) and Lepromatous (LL), "Primary case" (PC) had an incidence rate (IR) of 5 per 1000 person years of risk (PYR). Household contacts of Tuberculoid (TT) and borderline tuberculoid (BT) patients had an IR of 3.2 and 3.8 per 1000 PYR respectively. Compared with an incidence rate of leprosy of 1.6 per 1000 PYR among individuals not exposed to leprosy in the same area, household contacts of Non-lepromatous patients had a relative risk of twice as high and contacts of lepromatous and borderline lepromatous patients a relative risk of 3 times as high. The incidence rate was higher among household contacts of bacteriologically positive patients, among contacts closely related and in households with multiple cases. The peak age specific incidence rate among household contacts was between the ages 5-9 years of age. The significance of these findings are discussed.