Evaluation of NS1 protein detection for dengue-3 diagnosis in comparison to other laboratorial methods used in dengue diagnosis

Dengue virus infection represents the main arboviral disease worldwide, and it is of great importance to Brazil. Dengue encompasses a great spectrum of disease including asymptomatic infection, dengue fever, and even the severe form dengue hemorrhagic fever or dengue shock syndrome. Routine dengue diagnosis requires a sample collection in convalescence phase, but the experience shows that many patients do not return to collect this sample. For this reason a good diagnostic method of disease acute phase is fundamental to a correct management of the patient, reduction of disease complications and mortality rates, besides being very important to clinical and epidemiologic management in areas where multiple Flavivirus are endemic, such as in Brazil. In order to improve dengue diagnosis during acute phase of disease, this study evaluated the sensitivity and specificity of NS1 detection compared to virus detection by RT-PCR, serology and viral isolation in Ribeirão Preto. 250 samples of patients suspected of having dengue were evaluated. From the total of evaluated patients, in 81 (32,4%) molecular detection of dengue-3 virus was possible. By viral isolation 34 samples were positive by IFA and 51 positive by RT-PCR, on culture cell supernatants. IgM detection occurred in 26% of the samples. 36 positive samples to RT-PCR were negative for IgM detection because of collection day, mean of 2,1 days after the beginning of disease symptoms, and 22 samples were positive for IgM and negative for RT-PCR and viral isolation. Detection of anti-dengue IgG occurred in 103 (41,2%) samples. From these 32 (31% - 32/103) were positive for IgM and IgG detection, and from the samples positive only to IgG, 12 (16,90% - 12/71) were also positive to RT-PCR. NS1 test sensitivity was 76,2% and specificity 96,5% when compared to IgM detection or RT-PCR positive result. The positive predictive value in this case was 94,1% and the negative predictive value was 84,8%. When only IgM detection and RT-PCR positive results were considered, test sensitivity increased to 95,1% and specificity was 77,9%. The positive predictive value in this case was 45,9% and the negative predictive value was 98,9%. NS1 test presented better results than the diagnostic techniques usually used in acute phase of disease (RT-PCR and viral isolation), and also had a smaller decrease in positivity when compared to the days in which the samples were collected. The test presented a good performance, being able to detect dengue virus infection longer than RT-PCR and shortly the after beginning of disease symptoms. NS1 detection technique represents an important diagnostic tool in dengue infections, mainly in highly endemic areas, having a good specificity and sensitivity.