The primary diagnostic method for dengue infection is serological tests because they detect specific antibodies (IgM and IgG) or viral antigens (NS1) in the patient's blood. These tests provide rapid and reliable confirmation of dengue infection, especially after the acute febrile phase. Blood culture is not useful as the dengue virus is difficult to grow in standard culture media. Urine analysis and chest X-ray do not provide direct evidence of dengue infection. Early detection by serology aids in timely clinical management and preventing complications.

Reference: Harrison's Principles of Internal Medicine, Kasper et al., 20th Edition.