Acute hepatitis implies a condition lasting less than 6 months, culminating either in complete resolution of the liver damage with return to normal liver function and structure or a rapid progression of the acute injury toward extensive necrosis and a fatal outcome

Chronic hepatitis is defined as a sustained inflammatory process in the liver lasting longer than 6 months and is often impossible to differentiate from acute hepatitis on histologic criteria alone. Inflammatory cell extending beyond the limits of the portal tracts surrounding isolated nests of hepatocytes (piecemeal necrosis) and portal and/or central areas of the hepatic lobules connected by inflammation, necrosis, and col-lapse of architecture (bridging necrogis) are seen in severe forms of chronic hepatitis. However, these features may also be noted in uncomplicated acute hepatitis that ultimately re-solves completely. A purely histologic diagnosis of chronic hep-atitis usually requires evidence of progression toward cirrhosis,such as significant fibrous deposition and disruption of the hep-atic lobular architecture.

Both feces and blood from patients with hepatitis A con-tain virus during the prodromal and early icteric phases of the disease. Raw shellfish concentrate the virus from sewage pollu-tion and may serve as vectors of the disease. General hygienic measures should include handwashing by contacts and careful handling, disposal, and sterilization of excreta and contaminat-ed clothing and utensils. Close contacts of patients with hep-atitis A should receive immune serum globulin (ISG) as soon as possible but no later than 6 weeks after exposure. Travelers to endemic areas where sanitation facilities are poor may be protected by prior administration of ISG or by using hepatitis