There are now a variety of data bearing upon the question of whether Australia antigen (Au) is an infectious agent which causes hepatitis.
The association of Australia antigen with acute hepatitis is established and has been supported and confirmed by many throughout the world (Table 1).1-17
Australia antigen is associated with chronic hepatitis with an overall frequency of nearly 20% (Table 2).3,7,8,13,16,18-27
Australia antigen is distributed in institutions in a pattern expected for an infectious agent. For example, in large institutions for the mentally retarded (over 1,000 population) Australia antigen is found with Down's syndrome in a frequency of about 30%.28 In small institutions (under 50 population) it occurs in only 3%, whereas in Down's syndrome patients who live at home, Australia antigen has not been found to occur.
In Down's syndrome Au is associated with abnormalities of liver function28,29 and inflammatory abnormalities on liver biopsy.30