Background: As part of a larger study of the role of close contacts in the transmission of M. leprae, we explored whether the proportion of newly detected cases with a family history of leprosy differs with different incidence rates of leprosy in a population. Methods: Retrospective analysis was performed of contacts of all new leprosy patients diagnosed during a 10-yr period in well-established leprosy control programs in Thailand and Bangladesh. By our definition, a contact group consisted of the new case and of past and present cases who were relatives and in-laws of the new case. For a new case, the nearest index case was defined on the basis of time of onset of symptoms for the cases in the contact group, in combination with the level of closeness of contact between these cases and the new case. Three contact levels were distinguished. In Bangladesh these levels were defined as 'kitchen contact'; 'house contact'; and 'non-house contact'. In Thailand comparable levels were defined as 'house contact'; 'compound contact'; and 'neighbor contact'. Results: In Bangladesh 1333, and in Thailand 129 new patients were included. The average new case detection rate over 10 yrs was 50 per 100,000 general population per year in Bangladesh, and 1.5 per 100,000 in Thailand. In the high endemic area 25% of newly detected cases were known to belong to a contact group and were not the index case of this group, whereas in the low endemic area 62% of newly detected cases had these characteristics. The distribution of the nearest index cases over the three contact levels was comparable in both areas. Just over half of the nearest index cases were found within the immediate family unit ('kitchen' in Bangladesh; 'house' in Thailand). Conclusion: The results indicate that in a low endemic area a higher proportion of newly detected leprosy cases have a family history of leprosy compared to a high endemic area. Different contact levels and their relative risks to contract leprosy need to be established more precisely. In high endemic situations the circle of contacts that should be surveyed may need to be wider than currently practiced.</p
