Diagnosing yellow fever based on signs and symptoms can be difficult because early in its course, the infection can be easily confused with malaria, typhoid, dengue fever and other viral hemorrhagic fevers. If you have yellow fever, your blood may reveal the virus itself. If not, blood tests known as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) also can detect antigens and antibodies specific to the virus. Results of these tests may not be available for several days.
