Serodiagnostic Test Developed for Human Leptospirosis

Scientists at the Pasteur Institute of New Caledonia (Noumea, New Caledonia) working with their colleagues at the Pasteur Institute (Paris, France) tested 187 confirmed leptospirosis cases sera. There were 120 from New Caledonia, 38 from mainland France, 29 from French West Indies. Whole killed Leptospira fainei cells were used as the antigen for the test line and purified human immunoglobulin M (IgM) as the control line. The mobile phase was made of gold particles conjugated with goat anti-human IgM. The Microscopic Agglutination Test (MAT) was used as the gold standard with a cut-off titer of equal to or greater than 1:400.

Out of the 187 gold standard positive sera tested, 168 were RDT positive, including 15 RDT with a test line intensity graded as weak. Out of the 221 MAT-negative sera tested, 207 were RDT negative. All 14 RDT positive sera were graded weak and originated from nine healthy blood donors and five patients positive for anti-dengue virus IgM. The RDT sensitivity was 89.8% and the specificity 93.7%. This RDT had satisfactory reproducibility, repeatability, thermal tolerance, and shelf life. The comparison with MAT evidenced the earliness of the RDT to detect seroconversion. The Vertical Flow RDT developed displayed good diagnostic performances when compared with a lateral flow RDT (Leptocheck, Zephyr Biomedicals; Goa, India).

The authors concluded that because leptospirosis is endemic in New Caledonia and French West Indies, they considered both a MAT titer of 1:400 as a gold standard and a 1/400 dilution of the serum for the Vertical Flow RDT for evaluation. They wrote that it is highly probable that the use of a lower dilution of 1/200 or 1/100 would result in both an increased sensitivity and a decreased specificity. The use of the Vertical Flow RDT as an initial screen for leptospiral infections would still allow facilitating the difficult differential diagnosis of leptospirosis. The study was published on June 27, 2013, in the journal Public Library of Science Neglected Tropical Diseases.

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Pasteur Institute of New Caledonia
Pasteur Institute
Zephyr Biomedicals