This study investigated alternative VHF pathogens in patients clinically suspected of dengue but negative by standard diagnostics during a 2016 outbreak in central Vietnam.<h4>Methods</h4>Among 198 hospitalized patients, 52 dengue virus (DENV)-negative cases were tested using enzyme-linked immunosorbent assays for immunoglobulin G (IgG)/IgM against seven VHFs and molecular assays for pan-flaviviruses and hantaviruses. The gene discussed is CD40LG; the disease is dengue disease.