Infectious mononucleosis and related syndromes.

The "mono syndrome" is an acute febrile disease of older children and young adults which involves the lymphatic system and is characterized hematologically by the presence of 50% or more lymphocytes and monocytes and 10% or more atypical lymphocytes. Epstein-Barr virus (EBV) causes over 90% of the syndrome, cytomegalovirus (CMV) about 5% to 7%, and Toxoplasma gondii less than 1%. Viral hepatitis, adenovirus, rubella, and herpes simplex are rare causes. Only EBV produces classical heterophile-positive infectious mononucleosis. This article reviews the epidemiological and clinical features of this syndrome.