Diagnosis of leptospirosis by the gold standard serologic assay, the microscopic agglutination test (MAT), requires paired sera and is not widely available. We developed a rapid assay using immunodominant Leptospira immunoglobulin-like (Lig) proteins in a Dual Path Platform (DPP). This study aimed to evaluate the assay's diagnostic performance in the setting of urban transmission.
We determined test sensitivity using 446 acute and convalescent sera from MAT-confirmed case-patients with severe or mild leptospirosis in Brazil. We assessed test specificity using 677 sera from the following groups: healthy residents of a Brazilian slum with endemic transmission, febrile outpatients from the same slum, healthy blood donors, and patients with dengue, hepatitis A, and syphilis. Three operators independently interpreted visual results without knowing specimen status.
The overall sensitivity for paired sera was 100% and 73% for severe and mild disease, respectively. In the acute phase, the assay achieved a sensitivity of 85% and 64% for severe and mild leptospirosis, respectively. Within seven days of illness onset, the assay achieved a sensitivity of 77% for severe disease and 60% for mild leptospirosis. Sensitivity of the DPP assay was similar to that for IgM-ELISA and increased with both duration of symptoms (chi-square regression P = 0.002) and agglutinating titer (Spearman ρ = 0.24, P<0.001). Specificity was ≥93% for dengue, hepatitis A, syphilis, febrile outpatients, and blood donors, while it was 86% for healthy slum residents. Inter-operator agreement ranged from very good to excellent (kappa: 0.82–0.94) and test-to-test reproducibility was also high (kappa: 0.89).
The DPP assay performed acceptably well for diagnosis of severe acute clinical leptospirosis and can be easily implemented in hospitals and health posts where leptospirosis is a major public health problem. However, test accuracy may need improvement for mild disease and early stage leptospirosis, particularly in regions with high transmission.
Leptospirosis is an important cause of acute fever in the tropics and the mortality rate may exceed 15% in patients with severe disease manifestations. The gold standard serological test for diagnosing leptospirosis, the microagglutination test or MAT, requires significant laboratory resources and results are not timely. Improved diagnostics are therefore critically needed to identify patients and outbreaks earlier and to thereby prevent unnecessary deaths. The need for a rapid diagnostic test is particularly acute in resource-poor settings where leptospirosis is a major public health problem and sophisticated laboratories are unavailable. In this study, we measured the diagnostic accuracy of the novel Dual Path Platform (DPP) for leptospirosis using serum from patients with mild and severe disease. The DPP assay detected up to 85% of severe leptospirosis and 64% of mild leptospirosis patients using the initial clinical specimen collected at hospital presentation and its diagnostic performance was comparable to a commonly used IgM-ELISA. Furthermore, the DPP assay produces a result in 20 minutes and can be more easily implemented in field settings than existing diagnostic technologies. The commercially available DPP kit offers the simple, accurate, and quick diagnosis of leptospirosis and, consequently, more timely clinical and public health decision-making.