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Background  One of the most important drawbacks in visceral leishmaniasis (VL) population studies is the difficulty of diagnosing asymptomatic carriers. The aim of this study, conducted in an urban area in the Southeast of Brazil, was to evaluate the performance of serology to identify asymptomatic VL infection in participants selected from a cohort with a two-year follow-up period.    Methodology  Blood samples were collected in 2001 from 136 cohort participants (97 positive and 39 negatives, PCR/hybridization carried out in 1999). They were clinically evaluated and none had progressed to disease from their asymptomatic state. As controls, blood samples from 22 control individuals and 8 patients with kala-azar were collected. Two molecular biology techniques (reference tests) were performed: PCR with  Leishmania -generic primer followed by hybridization using  L. infantum  probe, and PCR with specific primer to  L. donovani  complex. Plasma samples were tested by ELISA using three different antigens:  L. infantum  and  L. amazonensis  crude antigens, and rK39 recombinant protein. Accuracy of the serological tests was evaluated using sensitivity, specificity, likelihood ratio and ROC curve.    Findings  The presence of  Leishmania  was confirmed, by molecular techniques, in all kala-azar patients and in 117 (86%) of the 136 cohort participants. Kala-azar patients showed high reactivity in ELISAs, whereas asymptomatic individuals presented low reactivity against the antigens tested. When compared to molecular techniques, the  L. amazonensis  and  L. infantum  antigens showed higher sensitivity (49.6% and 41.0%, respectively) than rK39 (26.5%); however, the specificity of rK39 was higher (73.7%) than  L. amazonensis  (52.6%) and  L. infantum  antigens (36.8%). Moreover, there was low agreement among the different antigens used (kappa<0.10).    Conclusions  Serological tests were inaccurate for diagnosing asymptomatic infections compared to molecular methods; this could lead to misclassification bias in population studies. Therefore, studies which have used serological assays to estimate prevalence, to evaluate intervention programs or to identify risk factors for  Leishmania  infection, may have had their results compromised.

Inaccuracy of Enzyme-Linked Immunosorbent Assay Using Soluble and Recombinant Antigens to Detect Asymptomatic Infection by Leishmania infantum