Person-to-person spread through the fecal-oral route is the primary means of HAV transmission. Peak infectivity in infected people occurs during the two-week period before the onset of jaundice when the concentration of virus in the stool is highest and most people are no longer infectious one week after jaundice onset. Before routine vaccination of children was recommended, children were a key source of infection because most infected children had no symptoms and could shed virus in stool for weeks or months. Transmission currently occurs primarily among susceptible adults.

Common-source outbreaks and sporadic cases can occur from exposure to fecally-contaminated food or water. Uncooked HAV-contaminated foods have been recognized as a source of outbreaks. Cooked foods also can transmit HAV if the temperature during food preparation is inadequate to kill the virus or if food is contaminated after cooking, as occurs in outbreaks associated with infected food handlers. Transmission of the virus from infected food handlers to food service establishment patrons is rare, accounting for 0.2% of the nearly 23,000 outbreak-associated cases of hepatitis A investigated by state health departments during 2016-2019. In 2020, there were 9,952 cases reported to public health, although CDC estimates that the actual number of cases was closer to 19,900. This represents a 47% decrease from 2019.

Until 2017, US incidence rates of hepatitis A were driven by occasional outbreaks, often linked to viral contamination of imported food. Since 2017, communitywide outbreaks have occurred more frequently, predominantly among people who are connected by specific risk factors, such as drug use or homelessness, and their close contacts.