Infectious mononucleosis (IM) is a self-limited viral syndrome caused primarily by Epstein-Barr virus (EBV), characterized by the classic triad of fever, pharyngitis, and posterior cervical lymphadenopathy, most commonly affecting adolescents and young adults aged 15–24 years. [1-2] EBV infects approximately 95% of the world population; symptomatic IM represents a minority of primary infections. [3]
1. History
- Sore throat — often the chief complaint; characterize severity, ability to swallow solids/liquids
- Fatigue/malaise — onset, severity, functional impact; often profound and disproportionate to other symptoms
- Fever — duration, pattern, peak temperature
- Timing — incubation period is 4–6 weeks; ask about recent close contacts, kissing, shared utensils/water bottles [2]
- Associated symptoms — headache, myalgias, anorexia, abdominal pain (LUQ → splenic concern), rash
- Important negatives — weight loss, night sweats, travel history, sexual history (HIV risk), immunosuppression, recent antibiotic use (amoxicillin rash?) [2][4]
2. Alarm Features
- Acute abdominal pain (especially LUQ) → splenic rupture (0.1–0.5% of cases; 80–86% are atraumatic; up to 9% mortality) [1][5]
- Stridor, drooling, inability to swallow → airway obstruction from tonsillar hypertrophy (most common cause of hospitalization, especially in children) [1][3]
- Petechiae, significant bleeding → thrombocytopenia or DIC
- Prolonged high fever, hepatosplenomegaly, cytopenias → hemophagocytic lymphohistiocytosis (HLH) [4]
- Neurologic symptoms (altered mental status, seizures, weakness) → meningoencephalitis, Guillain-Barré, cranial nerve palsy [4]
- Jaundice → severe hepatitis
- Immunocompromised patient → risk of fulminant EBV infection, lymphoproliferative disease [1]
3. Medications
- Avoid amoxicillin/ampicillin — causes a characteristic pruritic maculopapular rash in ~70–100% of IM patients; use alternative antibiotics if concurrent streptococcal pharyngitis is confirmed [2][6]
- Corticosteroids — NOT recommended for uncomplicated IM (SORT A, Cochrane review). Indicated only for: impending airway obstruction, hemolytic anemia, severe thrombocytopenia, or myocarditis [1][6-7]
- Antivirals (acyclovir, valacyclovir) — NOT recommended; no proven benefit in reducing severity or duration of symptoms [1][8]
- Supportive medications: acetaminophen or NSAIDs for fever and throat pain [4]
- Aspirin — avoid in children/adolescents (Reye syndrome risk)
4. Diet
- Encourage adequate fluid intake — dehydration risk from severe dysphagia [7]
- Soft foods if significant pharyngeal pain or tonsillar hypertrophy
- Avoid alcohol — hepatic transaminases are commonly elevated; alcohol may worsen hepatic inflammation
- No specific long-term dietary restrictions
5. Review of Systems
- HEENT: sore throat severity, dysphagia, voice changes (hot potato voice), ear pain
- Constitutional: fever, fatigue, night sweats, weight loss
- GI: abdominal pain (especially LUQ), nausea, anorexia, jaundice
- Heme: easy bruising, petechiae, bleeding gums
- Neuro: headache, neck stiffness, weakness, paresthesias
- Skin: rash (spontaneous or antibiotic-related)
- Respiratory: dyspnea, stridor
6. Collateral History and Family History
- Contacts — recent kissing partner, roommates, teammates with similar illness; EBV transmitted primarily through saliva [2]
- Immunodeficiency history — X-linked lymphoproliferative disease (Duncan syndrome) is a rare inherited condition with fatal susceptibility to EBV [1]
- Family history of lymphoma or autoimmune disease may be relevant given EBV's long-term associations [1]
- Athletic participation — critical to establish for return-to-play counseling
7. Risk Factors
- Age 15–24 years — peak incidence of symptomatic IM [1]
- College students, military recruits — close-quarters living [1]
- No prior EBV exposure — higher socioeconomic groups may have delayed primary infection, increasing risk of symptomatic IM in adolescence
- Immunosuppression — transplant recipients, HIV — risk of severe/fulminant disease and posttransplant lymphoproliferative disease (50% mortality) [1]
8. Differential Diagnosis
- Group A Streptococcal pharyngitis — can coexist with IM; rapid strep test should be performed [2]
- CMV mononucleosis — clinically indistinguishable from EBV mono; heterophile-negative; diagnosed by CMV IgM [1]
- Acute HIV infection — fever, pharyngitis, lymphadenopathy, rash; must consider in sexually active patients [9]
- Toxoplasmosis — lymphadenopathy, fatigue; heterophile-negative
- Acute hepatitis A/B — if transaminases are prominently elevated
- Lymphoma — persistent lymphadenopathy, B symptoms; cannot-miss diagnosis
- Peritonsillar abscess — unilateral tonsillar swelling, trismus, uvular deviation
- Diphtheria — rare but consider in unvaccinated patients with pharyngeal membrane
9. Past Medical History
- Prior episodes of pharyngitis or mononucleosis-like illness
- Immunosuppressive conditions — organ transplant, HIV, congenital immunodeficiency
- Splenectomy or splenic abnormalities
- History of autoimmune disease (false-positive heterophile antibodies possible) [9]
- Current medications, especially recent antibiotics
10. Physical Exam
- Vitals: fever (often low-grade), tachycardia; monitor for signs of airway compromise
- Oropharynx: tonsillar enlargement with exudate (>50% of patients), palatal petechiae (specificity 95%, LR+ 5.3) [10]
- Lymph nodes: posterior cervical adenopathy is most characteristic (specificity 87%, LR+ 3.1); also axillary and inguinal [10]
- Abdomen: LUQ tenderness; physical exam is unreliable for detecting splenomegaly (nearly universal but often not palpable) [2]
- Skin: maculopapular rash (especially if amoxicillin given), periorbital edema
- Hepatomegaly: present in ~10–15% of cases
- Assess airway: look for stridor, drooling, inability to handle secretions
11. Lab Studies
- CBC with differential — look for >50% lymphocytes and >10% atypical lymphocytes (LR+ 54 when both present). IM is unlikely if absolute lymphocyte count <4,000/mm³ [1][3][10]
- Rapid heterophile antibody test (Monospot) — sensitivity 87%, specificity 91%; 25% false-negative rate in the first week of illness; unreliable in children <5 years [1][9]
- Liver transaminases (AST/ALT) — elevated in majority of cases; elevated LFTs increase clinical suspicion when Monospot is negative [1]
- EBV-specific antibodies (if Monospot negative but clinical suspicion high):
- VCA IgM (+) without EBNA IgG → acute primary EBV infection [1][9]
- VCA IgG (+) with EBNA IgG (+) → past infection
- Rapid strep test or throat culture — to rule out concurrent GAS pharyngitis [2]
- CMV IgM — if heterophile-negative mononucleosis suspected [9]
- Consider HIV testing in at-risk patients with heterophile-negative mono-like illness [9]
The following figure illustrates a practical laboratory diagnostic algorithm:
12. Imaging
- Routine imaging is NOT indicated [1][7]
- Abdominal ultrasound — reliable for detecting splenomegaly but NOT routinely recommended; spleen size does not correlate with rupture risk [7]
- CT abdomen — indicated if splenic rupture is suspected (acute LUQ pain, hemodynamic instability)
- Lateral neck X-ray or CT neck — if concern for airway compromise or peritonsillar abscess
13. Special Tests
- Hoagland criteria — >50% lymphocytes + ≥10% atypical lymphocytes + fever + pharyngitis + adenopathy with confirmatory serology; specific but not sensitive [1]
- Centor/McIsaac score — useful to assess likelihood of GAS pharyngitis vs. IM in the sore throat patient
- Point-of-care Monospot — rapid, inexpensive, widely available
- Peripheral blood smear — atypical lymphocytes (Downey cells)
14. ECG
- Not routinely indicated
- Obtain ECG if: chest pain, palpitations, dyspnea, or syncope — myocarditis and cardiac conduction abnormalities are rare but recognized complications [1][4]
- Look for: ST changes, PR prolongation, arrhythmias
15. Assessment
- IM is a clinical diagnosis confirmed by laboratory testing [7]
- The classic presentation (fever + pharyngitis + posterior cervical lymphadenopathy in a 15–24-year-old) is highly suggestive [1]
- Atypical presentations: predominant hepatitis, prolonged fever without pharyngitis, neurologic manifestations, rash
- Children <5 years: often subclinical or atypical; heterophile antibodies frequently negative [9]
- Older adults (>40): less likely to have pharyngitis/lymphadenopathy; more likely to present with hepatitis and jaundice
- Symptoms typically resolve in 4–8 weeks, though fatigue may persist for 6 months or longer [1][7]
- Long-term associations: EBV linked to Hodgkin lymphoma, non-Hodgkin lymphoma, nasopharyngeal carcinoma, and a 32-fold increased risk of multiple sclerosis [1]
16. Treatment Plan
Initial/Supportive Care
- Acetaminophen or NSAIDs for fever and pain [4]
- Adequate hydration and nutrition
- Rest guided by symptoms; enforced bed rest is unnecessary [4][11]
Specific Situations
- Concurrent GAS pharyngitis → treat with antibiotics other than amoxicillin/ampicillin (e.g., azithromycin, cephalosporins) [2][6]
- Airway compromise → systemic corticosteroids (e.g., dexamethasone); ENT consultation; consider ICU if severe [6-7]
- Severe hematologic complications (hemolytic anemia, thrombocytopenia) → corticosteroids, hematology consultation [7]
Activity Restrictions
- No athletic activity for at least 3 weeks from symptom onset [1][6]
- Afebrile patients with adequate energy may begin supervised, low-intensity, nonimpact aerobic activity at 2 weeks [6]
- Contact/collision sports avoided for at least 3–4 weeks [2][6]
- Full return to sport only when afebrile, clinically well, and symptoms resolved; use shared decision-making [1][7]
17. Disposition
Discharge criteria (majority of patients)
- Able to tolerate oral fluids
- No signs of airway compromise
- No hemodynamic instability
- Reliable follow-up and understanding of return precautions
Admission criteria
- Airway obstruction or impending compromise [1][3]
- Suspected splenic rupture — hemodynamic instability, acute abdomen
- Severe dehydration from inability to swallow
- Severe hepatitis or hematologic complications (HLH, hemolytic anemia, severe thrombocytopenia) [1]
- Immunocompromised patients with severe disease
Specialist consultation triggers
- ENT — tonsillar hypertrophy with airway concern, peritonsillar abscess
- Surgery — suspected splenic rupture
- Hematology — cytopenias, suspected HLH
- Infectious disease — immunocompromised patients, atypical/severe presentations
18. Follow Up / Return Precautions
Follow-up timing
- Primary care follow-up in 1–2 weeks to reassess symptoms, activity tolerance, and labs if indicated
- Athletes: reassess at 3 weeks for return-to-play decision [1][6]
Return precautions — instruct patients to seek immediate care for:
- Sudden, severe left-sided abdominal pain (splenic rupture — ~80% occur within 3 weeks of symptom onset) [1][5]
- Difficulty breathing, stridor, or inability to swallow
- Significant bleeding, bruising, or petechiae
- High fever unresponsive to antipyretics
- Neurologic symptoms — severe headache, confusion, weakness, seizures
Patient counseling
- Avoid sharing drinks, utensils, and kissing during acute illness (virus sheds in saliva for a median of 6 months) [8]
- Fatigue may persist for weeks to months; gradual return to normal activity is expected [4]
- Most patients recover fully within 2 months without sequelae [4]
- Hospitalization is required in <1% of cases [1]
References
1. Infectious Mononucleosis: Rapid Evidence Review. — Sylvester JE, Buchanan BK, Silva TW. American Family Physician. 2023.
2. Selected Issues for the Adolescent Athlete and the Team Physician: A Consensus Statement. — Medicine and Science in Sports and Exercise. 2008.
3. Common Questions About Infectious Mononucleosis. — Womack J, Jimenez M. American Family Physician. 2015.
4. Infectious Mononucleosis. — Luzuriaga K, Sullivan JL. The New England Journal of Medicine. 2010.
5. Splenic Rupture or Infarction Associated With Epstein-Barr Virus Infectious Mononucleosis: A Systematic Literature Review. — Toti JMA, Gatti B, Hunjan I, et al. Swiss Medical Weekly. 2023.
6. The Adolescent Athlete and the Team Physician: A Consensus Statement. 2025 Update. — Putukian M, Leclere LE, Herring SA, et al. Medicine and Science in Sports and Exercise. 2026.
7. American Medical Society of Sports Medicine Position Statement: Mononucleosis and Athletic Participation. — Putukian M, McGrew CA, Benjamin HJ, et al. Clinical Journal of Sport Medicine : Official Journal of the Canadian Academy of Sport Medicine. 2023.
8. Antiviral Agents for Infectious Mononucleosis (Glandular Fever). — De Paor M, O'Brien K, Fahey T, Smith SM. The Cochrane Database of Systematic Reviews. 2016.
9. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). — Miller JM, Binnicker MJ, Campbell S, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2024.
10. Does This Patient Have Infectious Mononucleosis?The Rational Clinical Examination Systematic Review. — Ebell MH, Call M, Shinholser J, Gardner J. The Journal of the American Medical Association. 2016.
11. Epstein-Barr Virus Infectious Mononucleosis. — Ebell MH. American Family Physician. 2004.