Infectious mononucleosis

What it is

Infectious mononucleosis, also called glandular fever, is caused predominantly by the Epstein-Barr virus (EBV). Transmission is mainly by saliva and droplet, which is why it is known as the kissing disease, and adolescents are especially susceptible.

It is common: more than 90% of the adult population worldwide is EBV-antibody positive, the incidence in US is 5:1000 population a year, and the peak age is 15-24 years. The incubation period is about 6 weeks and symptoms usually last 2-4 weeks. It is often asymptomatic in young children.

How it presents

• Fever.
• Tonsillitis or pharyngitis with or without exudates, which can be a severe membranous tonsillitis.
• Posterior or diffuse cervical lymphadenopathy, especially the posterior nodes of the neck.
• Significant fatigue.
• Palatal petechiae, written also as palatine petechial hemorrhage.
• Hepatosplenomegaly.

Sore throat with splenomegaly is infectious mononucleosis until proven otherwise.

How it is diagnosed

• Monospot test, the heterophile antibody test. It carries a 25% false-negative rate during the 1st week of illness, so it could be negative in the first week.
• If suspicion persists despite a negative monospot test, EBV-specific antibody serology. A negative monospot test may instead mean CMV.
• Blood film, or peripheral smear: atypical lymphocytosis with leukocytosis, and the atypical lymphocytes are large with irregular nuclei.
• Paul-Bunnell test.
• Transient hepatitis may be found.