As the number of leprosy cases is reducing, so too is the clinical expertise even in endemic countries. This often leads to delay or misdiagnosis and delayed initiation of MDT. Early detection and treatment of leprosy are important to prevent disability but may also aid in breaking the transmission chain.
As identified in both the road map and the DTAG meeting report, a test confirming (or ruling out) leprosy of all types, including indeterminate and PB leprosy, is of high priority. The purpose of this TPP is to guide the development of a tool that can be used at all health-care levels where MDT is prescribed, to aid health-care providers in deciding when to initiate treatment. The clinical validation of such a test should take into account performance requirements for the entire spectrum of leprosy, including manifestations with low levels of bacilli. Although ideally such a test would be available as a point-of-care test, it is recognized that to reach the required sensitivity and specificity, laboratory-based testing might be required.
The TPP target performance characteristics were modelled to reduce health-care provider delays in diagnosis as a function of diagnostic performance. In the modelling, prevalence of leprosy in tested populations assumed endemicity levels similar to household contacts, as this would be the most likely group to seek medical consultation. It was observed through modelling that, to have a meaningful impact on reduction on time to diagnosis, very high stringency around specificity is required. It is of note that in cases where performance requirements are high and cannot be met with a single test, a combined, twostep test approach may be used to achieve the required testing specificity.