Duration of Illness in Infectious Mononucleosis
Most patients with infectious mononucleosis experience acute symptoms for 2-4 weeks, with fatigue potentially persisting for 3 months, though 6-11% may have symptoms lasting beyond 100 days. 1, 2, 3
Acute Phase Duration
- The acute symptomatic phase typically lasts 2-4 weeks, during which patients experience the classic triad of fever, tonsillar pharyngitis, and lymphadenopathy 1, 2
- Fever and sore throat generally resolve within the first 2-3 weeks of illness 2
- Lymphadenopathy and pharyngeal symptoms are most prominent during the first 2 weeks 1
Fatigue and Recovery Timeline
- Fatigue is the most persistent symptom and tends to resolve within 3 months in the majority of patients 1, 2
- However, fatigue, myalgias, and increased need for sleep may persist for several months after the acute infection has resolved 2
- In student populations studied, 11% of patients reported symptom persistence beyond 100 days, and 6% had symptoms lasting more than 1 year 3
Post-Acute Symptoms
- During the convalescent phase, patients commonly experience getting tired easily, daytime sleepiness, and depression as the most significant ongoing symptoms 3
- These post-acute symptoms occur significantly more frequently than in patients recovering from other upper respiratory infections 3
- Poor physical functioning during the acute phase—including lengthy convalescence and reduced activity levels—consistently predicts prolonged illness 4
Activity Restrictions
- Patients should avoid contact sports and strenuous exercise for at least 4-8 weeks after symptom onset due to risk of splenic rupture 1, 2
- Bed rest should not be enforced; rather, the patient's energy level should guide activity, as early mobilization may actually facilitate faster recovery 2, 4
- Splenomegaly, present in approximately 50% of cases, typically resolves within 4-8 weeks but may persist longer 1
Important Clinical Caveats
- There is a distinct fatigue syndrome that can develop after infectious mononucleosis, and this represents a risk factor for chronic fatigue syndrome 1, 4
- The heterophile antibody test typically becomes positive between days 6-10 after symptom onset, so early testing may yield false-negative results 5, 2
- Immunocompromised patients may experience more severe and prolonged disease courses with increased risk of complications 6, 5