Mycobacterium leprae soluble antigen (Rees) skin test responses in an endemic population in India.

The response to intradermal administration of Rees soluble skin test antigen was studied in 12,142 randomly selected individuals living in a highly endemic area in South India. Taking a cut-off point of 12 mm induration as the criterion for 'positivity', 73% of PB cases, 45% of MB cases and 63% of noncase population (67% in contacts and 63% in non-contacts) were found to be positive. Age-specific positivity rates were higher in males than in females and in adults than in children. The difference in age-adjusted positivity rates between cases, contacts an noncontacts in the female population was found to be significant. However, the differences in reaction response are not sufficient to identify the sub-populations of cases, contacts and noncontacts and as such this antigen is not likely to be useful in epidemiological studies of infection and evolution of clinical disease in high endemic populations.