Dengue fever and dengue hemorrhagic fever (DHF) are acute viral infections primarily found in tropical regions, caused by four closely related serotypes of the Dengue virus, a member of the Flavivirus genus in the Flaviviridae family. This test detects the presence of the NS1 antigen in the serum, which is a key marker for early-stage Dengue infection. The NS1 antigen is present in high concentrations during the initial phase of infection and is detectable from the first day of fever onset.