Serodiagnosis of leprosy and follow-up of household contacts using a commercial rapid test containing ND-O/LID-1 antigens
Introduction: Early diagnosis of leprosy, including the diagnosis of sub-clinical disease in contacts of known cases, would be a major advance. The signs of early leprosy are often difficult to assess and a reliable diagnostic test could play an important role in identifying cases and thus reducing transmission.
Methods: Subjects were recruited at Centro de Sau´de Jardim Guanabara, Rondono´polis, Mato Grosso State, Brazil. Sera were obtained from 174 recently diagnosed leprosy patients, 409 household contacts, 53 endemic controls and 12 patients with active TB. 186 of the household contacts were re-tested on subsequent visits. Both the NDO-LIDw rapid test (Orange Lifew, Rio de Janeiro, Brazil) and an anti-PGL-1 ELISA test were used on all samples for comparison.
Results: LID-1 was positive in 25 of 125 PB cases (20%), but in 41 of 49 MB cases (83·7%), while the anti-PGL-1 ELISA was positive in 8 (6·4%) and 35 (71·4%) cases, respectively. Specificity for LID-1 was 85% and for the anti-PGL-1 ELISA, 97%. Amongst household contacts, 9 of 409 (2·2%) were positive on the LID-1 test, and a further 51 (12·5%) were weakly positive; although 9 cases of leprosy were subsequently identified amongst these contacts, 6 had tested negative, 2 were weakly positive and only 1 had been positive.
Conclusion: The ND-O-LID-1 assay can be easily performed by the addition of serum to the assay device, and thus can be applied in resource-poor settings. The test was found to be useful for the detection of multibacillary cases, which in the long term will help to reduce transmission of the disease. This is a specific test, but it is not very sensitive for early detection of leprosy in household contacts and paucibacillary forms.