Rapid detection of human Leishmania infantum infection: a comparative field study using the fast agglutination screening test and the direct agglutination test

This study aimed to evaluate the performance of a fast agglutination screening test (FAST) for serodiagnosis of human Leishmania infantum infection in Iran. FAST is based on the direct agglutination test (DAT) but combines with a higher parasite concentration and is performed with only one serum dilution. The validity of FAST for the detection of L. infantum infection in the field was compared with the direct agglutination test on 110 confirmed or patients suspected of infection with leishmaniasis, 177 healthy individuals and 41 patients with other infectious diseases who were from northwestern and southern parts of Iran. In this study, we found a 1:1600 cut-off point empirically by seeking the best correlation (90.8) between sera confirmed with visceral leishmaniasis and healthy control sera. A sensitivity of 95.4% (95% CI, 91.4-99.4) and specificity of 88.5% (95% CI, 84.2-92.8) were found with 1:1600 as a cut-off titer when DAT-confirmed cases were compared with the control groups. A good degree of agreement was found between FAST and DAT (90.8%) by Kappa analysis. FAST requires 2?h for reading the results versus the 12-18?h needed for DAT. As FAST is simple, rapid, sensitive and non-invasive and does not require a higher volume of antigens or much expertise, it can be used for screening and serodiagnosis of human L.?infantum infection.