Diagnosis of HAV infection requires thedetection of either immunoglobulin M (IgM) anti-HAV in serum or HAV RNA in serum or stool.IgM anti-HAV, a marker of acute illness, becomes detectable within 5–10 days of theonset of symptoms in the majority of persons (58,62), usually peaks within 1 month of illness, and decreases toundetectable levels within 6 months after infection (58,62–64) (Figure 2).However, positive tests for IgM anti-HAV in persons >1 year after infection have beenreported, as have likely false-positive tests in persons without evidence of recent HAVinfection (65–67). This evidence concerns the gene CD40LG and infection.