Dengue virus serotype 4 infection diagnosed not by rapid antigen test, but by real-time reverse transcription-PCR and enzyme-linked immunosorbent assay: A case report.

A 39-year-old Japanese male visited our hospital with fever, headache, and joint pain after a 5-day trip to Malaysia. Blood tests revealed decreased white blood cell and platelet counts. Although dengue was suspected, a rapid diagnostic test (RDT) on the 5th day after symptom onset was negative for dengue virus (DENV) nonstructural protein 1 (NS1) antigen, DENV IgM antibody, and DENV IgG antibody. Since dengue could not be ruled out in light of the clinical symptoms, an additional real-time reverse transcription-PCR (RT-PCR) test and enzyme-linked immunosorbent assay (ELISA) were performed. The DENV serotype 4 (DENV-4) genome was detected in the serum using real-time RT-PCR. DENV NS1 antigen, IgM antibody, and IgG antibody were detected in the serum using ELISA. This is a case of dengue diagnosed based not on RDT but on real-time RT-PCR and ELISA. When RDT results are negative, but dengue is suspected, additional real-time RT-PCR or ELISA testing must be performed to correctly diagnose patients with DENV infection.