Intrafamilial transmission of leprosy in Vellore Town, India

A hospital-based study was done from 1968 to 1991 to determine the risk and extent of intrafamilial transmission of leprosy in relation to the characteristics of the index cases and contacts in urban areas in India. Families were examined by doctors annually. Skin smears were done for contacts of multibacillary (MB) leprosy patients. Person years of follow up were computed for each contact and used as the denominator for computation of incidence rates. Specific rates were computed by age, sex, type of leprosy, smear in index cases, age at registration, and sex of contacts. Of the 120 index cases (81 males, 39 females) 44% were MB; 410 contacts (186 males, 224 females) and 14 co-prevalent cases were registered. The cumulative years of follow up was 2725 years. Fourteen contacts developed the disease (9 TT, 3 indeterminate, and 2 BT); 85.7% were in the 0-14 age group; 12 of 14 patients were detected to have leprosy during the first 5 years. The incidence rate (IR) was 5.1/1000 (males 5.15, females 5.12). The IR was 7.3/1000 and 2.3/1000 among contacts of MB and paucibacillary leprosy patients (p < 0.05). The IR in multiple-case families was 1.8. The importance of active surveillance by a hospital-based survey is emphasized. It should be designed to focus on children younger than 15 years and should be limited to 5 years of follow up.