Impact of age and immune status on the accuracy of rapid diagnostic tests for visceral leishmaniasis in Brazil.

Background: Visceral leishmaniasis (VL) represents a significant public health concern due to its high case-fatality, which poses the challenge of a timely and accurate diagnosis. Antibody-based rapid diagnostic tests (RDTs) have emerged as a disruptive innovation in recent years, by offering a diagnosis in the field, at low cost, easy to perform and with results in a few minutes. However, their performance can vary across regions and different subgroups, particularly in immunocompromised individuals. This study aimed to assess the accuracy of VL RDTs registered with the Brazilian national regulatory agency, or available through the PAHO strategic fund, considering diverse patient profiles.

Methodology/principal findings: Three commercially RDTs were identified LSH Ab Eco Teste, Leishmaniasis VH Bio, and Kalazar Detect and evaluated using a well characterized panel of serum samples (n = 300) from suspected VL patients from different Brazilian regions. Sensitivity, specificity, and accuracy were determined for different patient's ages and HIV coinfection status. Overall, RDTs exhibited lower sensitivity in children under 3 years old and HIV co-infected individuals compared to those over 3 years without HIV co-infection (p < 0.05). The agreement (Cohen's kappa coefficient) between observers (reproducibility) and intra-test (repeatability) for all three commercial kits was excellent.

Conclusions/significance: While RDTs offer desirable advantages in terms of access to diagnoses, variation on their performance imposes limits on their implementation. The performance of RDTs for VL exhibits significant differences related to age and immune status.