In a recent article (6), Wang et al. reported an extensive evaluation of NS1 antigen and compared it with real-time PCR, an IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA), and a hemagglutination inhibition assay for diagnosis of dengue virus infection. The authors reported MAC-ELISA positivity for 46 (92) out of 50 samples positive for dengue virus by real-time PCR (RT-PCR). However, the literature suggests (5) that viremia in dengue lasts for less than 5 days and that the IgM antibody response takes 5 to 10 days to develop in cases of primary dengue virus infection and 4 to 5 days in cases of secondary dengue virus infection (2, 5). Hence, at a particular time postinfection, it is unlikely that the results for both of these tests will be positive. The authors report that they were able to detect viral RNA up to 8 days postinfection. However, this also does not explain the overlap period, as it does not explain why RT-PCR positivity was observed in only 1 out of 100 dengue virus IgM-positive samples. It is important to know in how many cases the virus genome could be detected until day 8 out of the 50 samples that were positive by real-time PCR. It would also be valuable to know whether the same patient's blood was drawn for 8 consecutive days and checked for viremia and, if so, whether the virus was detectable.
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