Characterized by the classic triad of fever, pharyngitis, and lymphadenopathy, along with atypical lymphocytosis.
Often subclinical in young children.
Positive heterophile antibody test and serologic test for antibodies against EBV are usually diagnostic.
Rare but potentially life-threatening complications include severe upper airway obstruction, splenic rupture, fulminant hepatitis, encephalitis, severe thrombocytopenia, and hemolytic anemia.
Treatment is usually symptomatic.
Infectious mononucleosis (IM) is a clinical syndrome in a patient with primary Epstein Barr virus (EBV) infection; other causes of mononucleosis syndrome are much less common. The diagnosis "infectious mononucleosis" is primarily used when the syndrome is caused by EBV; "mononucleosis syndrome" should be used when the syndrome is caused by a non-EBV etiology. In children and adolescents EBV has been found to be the cause of IM in 80% to 90% of cases. 
Non-EBV mononucleosis syndrome may also be caused by human herpes virus 6 (9%), CMV (5% to 7%), HSV-1 (6%), and rarely by Streptococcus pyogenes , Toxoplasma gondii , HIV-1, adenovirus, as well as Corynebacterium diptheriae , Francisella tularensis , hepatitis A and B viruses, rubella, or enteroviruses. This syndrome may also be caused by connective tissue disorders, malignancies, and drug reactions.   
IM typically manifests in adolescents and young adults as a febrile illness with sore throat and enlarged lymph nodes. Atypical lymphocytosis and a positive heterophile antibodies test are usually observed. The disease is generally mild in children, but more severe in adults. Resolution of the acute illness is usually followed by a lifelong latent infection, with over 90% of the adult population infected worldwide. 
EBV infection can be asymptomatic, cause mild, nonspecific symptoms, or cause IM with symptoms and fatigue lasting up to 6 months or more.
Missouri Department of Health and Senior Services
Adjunct Assistant Professor of Clinical Pediatrics
Washington University School of Medicine
Adjunct Associate Professor of Pediatrics
Child Health Department
University of Missouri
GT declares that he has no competing interests.
College of Medicine
University of Malawi
LK declares that she has no competing interests.
Division of Infectious Diseases
Associate Professor of Medicine
Divisions of Infectious Diseases and General Internal Medicine
Johns Hopkins University School of Medicine
PGA declares that he has no competing interests.
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