Person-to-person by the fecal-oral route. The infectious agent is found in feces, reaches peak levels the week or two before onset of symptoms, and diminishes rapidly after liver dysfunction or symptoms appear, which is concurrent with the appearance of circulating antibodies to HAV.

Common source outbreaks have been related to contaminated water; food contaminated by infected food handlers, including foods not cooked or handled after cooking; raw or undercooked mollusks harvested from contaminated waters; and contaminated produce such as lettuce and strawberries. Several outbreaks have been associated with injecting and non-injecting drug use. Transmission through transfusion of blood and clotting factor concentrates obtained from viremic donors during incubation has been reported, albeit rarely.