Performance of rK39-based immunochromatographic rapid diagnostic test for serodiagnosis of visceral leishmaniasis using whole blood, serum and oral fluid.

The performance of Kalazar Detect RDT in whole blood and serum was similar; however, using oral fluid, the sensitivity was low. Particularly in samples from the city of Natal, Rio Grande do Norte state in Northeastern Brazil, we observed low sensitivity, 80.0% (95% CI: 62.7-90.5), using whole blood and serum, and poor sensitivity, 43.3% (95% CI: 27.4-60.8) with oral fluid. Those values were much lower than in the other regions, where sensitivity ranged from 92.7-96.3% in whole blood and serum, and 80.0-88.9% in oral fluid. Besides, in VL/aids coinfected patients, lower sensitivity was achieved compared with VL patients. In samples from Natal, the sensitivity was 0.0% (95% CI: 0.0-49.0) and 25.0% (95% CI: 4.6-69.9), using oral fluid and serum/whole blood, respectively; in samples from the other regions, the sensitivity ranged from 40.0-63.6% and 80.0-81.8%, respectively. As for specificity, high values were observed across the fluids, 100.0% (95% CI: 96.5-100.0) in whole blood, 96.3% (95% CI: 90.8-98.5) in serum, and 95.3% (95% CI: 89.5-98.0) in oral fluid; across localities, specificity ranged from 85.7-100.0%. Serum samples sent by the collaborating centers to Instituto de Medicina Tropical (n = 250) were tested by Kalazar Detect RDT, Direct Agglutination Test, Indirect immunofluorescence assay, Enzyme-linked immunosorbent assay, and IT-Leish® RDT. The regional difference in the performance of rK39-based RDT and lower sensitivity in Leishmania/HIV coinfected patients raise concern on the routine use of these products for the diagnosis of VL.