Clinical and Virological Factors Influence Dengue Immunoassay

A team from the Institute Pasteur in Phnom Penh (Cambodia) collected blood from patients hospitalized during the 2006 and 2007 dengue epidemics in Cambodia. Blood samples were tested for hematocrit and platelet count as well as for other biological parameters necessary for patients' follow-up. Sera were tested for dengue using serology and molecular methods at the Institute Pasteur in Cambodia. Dengue infection was confirmed in 243 of 339 symptomatic patients and in 17 asymptomatic individuals out of 214 household members tested.

Overall sensitivity and specificity of Platelia NS1 Ag kit were 57.5% and 100% respectively. When the NS1 Ag assay was combined with immunoglobulin IgM antibody capture ELISA, the sensitivity was significantly increased for dengue diagnosis. NS1 Ag positivity rate was found significantly higher in dengue fever (DF) cases than in fatal dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). It was higher in primary rather than in secondary infections, in patients with a high viremia (>5 log/mL), and in patients infected with the dengue viral strain DENV-1. In asymptomatic individuals, the NS1 Ag capture sensitivity tends to be lower than that in symptomatic patients. Milder disease severity was observed independently in patients with ribonucleic acid (RNA) copy number >5 log10 complementary DNA (cDNA) equivalents/mL or in high level of NS1 antigen ratio or in DENV-1 infection.

The authors concluded that the overall sensitivity of the Platelia Dengue NS1 Ag detection kit (BioRad; Hercules, CA, USA) varied widely across the various forms of dengue infection or disease. Sensitivity was highest in patients sampled during the first three days after onset of fever, in patients with primary infection, DENV-1 infection, with high level of viremia and in DF rather than DHF/DSS. The semi-quantitative approach of the test, demonstrated that the NS1 antigen level was significantly correlated to the level of viremia and that the low level of NS1 antigen was associated with more severe disease. The study was published online on July 19, 2011, in the Public Library of Science Neglected Tropical Diseases.

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