The incubation period of infectious mononucleosis in adolescents is 30–50 days. In children, it may be shorter. The majority of cases of primary EBV infection in infants and young children are clinically silent. In older patients, the onset of illness is usually insidious and vague.
Prodrome of Illness:
Patients may complain of malaise, fatigue, acute or prolonged (>1 wk) fever, headache, sore throat, nausea, abdominal pain, and myalgia. This prodromal period may last 1–2 wk. The complaints of sore throat and fever gradually increase until patients seek medical care. Splenic enlargement may be rapid enough to cause left upper quadrant abdominal discomfort and tenderness, which may be the presenting complaint.
The physical examination is characterized by generalized lymphadenopathy (90% of cases), splenomegaly (50% of cases), and hepatomegaly (10% of cases).
Lymphadenopathy occurs most commonly in the anterior and posterior cervical nodes and the submandibular lymph nodes and less commonly in the axillary and inguinal lymph nodes. Epitrochlear lymphadenopathy is particularly suggestive of infectious mononucleosis.
Symptomatic hepatitis or jaundice is uncommon, but elevated liver enzymes are common.
Splenomegaly to 2–3 cm below the costal margin is typical; massive enlargement is uncommon.
The sore throat is often accompanied by moderate to severe pharyngitis with marked tonsillar enlargement, occasionally with exudates . Petechiae at the junction of the hard and soft palate are frequently seen. The pharyngitis resembles that caused by streptococcal infection.
Other clinical findings may include rashes and edema of the eyelids.
Rashes are usually maculopapular and have been reported in 3–15% of patients. Up to 80% of patients with infectious mononucleosis experience “ampicillin rash” if treated with ampicillin or amoxicillin. This vasculitic rash is probably immune mediated and resolves without specific treatment.