The US Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) are investigating a multistate hepatitis A outbreak linked to imported frozen clams.At least 37 people have been infected across four states, according to the CDC. Thirty people have been hospitalized, while no deaths have been reported.Cases have been reported in Massachusetts (three), Minnesota (three), New York (27) and Pennsylvania (four). Those infected range in age from 6 to 40 years.Raw Shellfish Linked to OutbreakHealth officials interviewed people about foods they consumed before falling ill. The CDC said:“Of the people interviewed, 77% reported eating ceviche (raw fish or shellfish marinated in citrus juice), 76% reported eating raw or undercooked shellfish, and 47% reported eating raw or undercooked conchas negras (black clams),” the CDC said.Further analysis found that imported frozen clams were the likely source of the infection.The CDC said the actual number of illnesses is likely higher than the 37 reported cases. Some people may recover without seeking medical care and therefore may not be tested for hepatitis A. Recent illnesses may also not yet have been linked to the outbreak because it can take weeks to determine whether an individual case is part of an outbreak.Frozen Clam Products RecalledLa Serranita-brand concha negra (black shell) shell meat products were recalled by dealers in New York and New Jersey in April.The shell meat products, imported from Ecuador, were distributed to restaurants and retailers in Connecticut, Massachusetts, New Jersey, New York, Ohio and Pennsylvania and may have been distributed elsewhere.What To Do If You Were ExposedIf you ate frozen La Serranita-brand concha negra shell meat raw or undercooked within the past 14 days and are not vaccinated against hepatitis A, contact your local health department or healthcare provider to discuss treatment, including post-exposure prophylaxis, the CDC said.What Is Hepatitis A?Hepatitis A is a liver infection caused by the hepatitis A virus (HAV). It spreads when people consume food or water contaminated with the virus or through close contact with an infected person. Hepatitis A is preventable through vaccination.Hepatitis A SymptomsNot everyone infected with hepatitis A develops symptoms. When symptoms occur, they usually appear 2–7 weeks after exposure and can include:Dark urine or clay-colored stoolsDiarrheaFeeling tiredFeverJoint painLoss of appetiteNausea, stomach pain or vomitingYellowing of the skin or eyes (jaundice)Adults are more likely than children to develop symptoms. People with hepatitis A may feel sick for several weeks to several months but usually recover completely.In rare cases, hepatitis A can lead to hospitalization, liver failure and death. Severe disease is more common in older people and those with other serious health conditions, such as chronic liver disease.