Multiple hepatitis viruses in multiple attacks of acute viral hepatitis

We evaluated the causes of 30 episodes of acute viral hepatitis in 13 patients who had multiple attacks. Two (seven per cent) of 30 bouts were caused by hepatitis A virus, and 12 (40%) by hepatitis B virus. No patient, however, had more than one attack with the serologic characteristics of Type A or Type B disease. Thus, there were 16 bouts (53 per cent) not attributable to either of the two recognized hepatitis viruses. None of these "non-A, non-B" episodes, evaluated for infectious mononucleosis and cytomegalovirus infection, could be ascribed to either. From this evidence, therefore, it appears that the clinical syndrome of viral hepatitis is produced not only by the two viruses (hepatitis A virus and hepatitis B virus) recognized since the 1940's but also, in all probability, by two non-A, non-B agents.