Continuing Education Activity

Infectious mononucleosis remains a common clinical condition worldwide, most often caused by Epstein-Barr virus and characterized by fever, pharyngitis, lymphadenopathy, fatigue, and variable systemic manifestations. Although frequently self-limited, the disease carries important diagnostic and management considerations. This course reviews the differentiation from other causes of mononucleosis-like syndromes, such as cytomegalovirus, acute HIV infection, group A Streptococcus, toxoplasmosis, medication-related reactions, and malignancy, as well as the pathophysiology, clinical presentation, laboratory evaluation, and potential complications. Participants will gain an understanding of characteristic and atypical presentations, evidence-based supportive management strategies, high-risk patients and complications, and guidance regarding activity restrictions and follow-up. This activity for healthcare professionals is designed to enhance the learner's competence in identifying  infectious mononucleosis, performing the recommended evaluation, and implementing an appropriate interprofessional approach when managing this condition.

Objectives:

• Identify the various clinical presentations of infectious mononucleosis that warrant evaluation for alternative diagnoses.
• Select appropriate laboratory testing for suspected infectious mononucleosis.
• Implement evidence-based management plans for infectious mononucleosis.
• Collaborate with interprofessional team members to improve care coordination and outcomes for individuals with infectious mononucleosis.

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Introduction

Infectious mononucleosis, an extremely common infection with widespread global distribution, classically presents with fever, lymphadenopathy, and tonsillar pharyngitis. The term “infectious mononucleosis” was first used in the 1920s to describe a group of college students with a similar pharyngeal illness and blood laboratory findings of lymphocytosis and atypical mononuclear cells. Epstein-Barr virus (EBV) was later established as the cause of infectious mononucleosis after an exposed healthcare worker developed a positive heterophile test.[1]

Etiology

EBV, also known as human herpesvirus 4, causes infectious mononucleosis and remains one of the most widely disseminated viral infections worldwide, with more than 95% of adults demonstrating evidence of prior infection.[2] Several other infectious agents can produce a mononucleosis-like syndrome, including cytomegalovirus (CMV), human immunodeficiency virus (HIV), group A Streptococcus, adenovirus, and enteroviruses. Toxoplasmosis frequently presents with fever and lymphadenopathy, but causes pharyngitis less commonly than EBV-associated infectious mononucleosis.

Noninfectious conditions may also mimic the clinical presentation of mononucleosis. Potential causes include medication-related reactions associated with certain antibiotics, carbamazepine, and immunosuppressive agents, eg, tacrolimus. Lymphoma represents another important noninfectious cause that should remain in the differential diagnosis when evaluating patients with mononucleosis-like symptoms.[3][4]

Epidemiology

EBV is one of the most widespread human pathogens, with an estimated 95% of adults seropositive.[2] Once infected, the virus establishes a lifelong latent infection and can periodically reactivate. Humans are thought to be the only major reservoir. When EBV is acquired in childhood, infection typically doesn't result in clinical symptoms. Symptomatic infection increases in frequency during adolescence and early adulthood, with symptomatic disease uncommon later in adulthood. However, when infection does occur later in adulthood, it can result in more severe disease.[5][6]

EBV acquisition is in part related to socioeconomic factors, eg, crowded living conditions and access to good hygiene. In settings with poor access to good hygiene, almost all children are seropositive for the EBV virus by the age of 6 years. In settings with better access to hygiene, EBV seroconversion increases between ages 2 and 4 years and again between 14 and 18 years, with 70% achieving seroconversion during childhood and 90% in adulthood.[7]

Significant demographic disparities in infectious mononucleosis exist within the United States, largely reflecting socioeconomic factors that influence the age at which EBV infection occurs. Black or African American and Hispanic populations demonstrate higher EBV seroprevalence rates, whereas White populations experience the highest rates of symptomatic infectious mononucleosis. This pattern suggests earlier EBV exposure among non-White populations, resulting in a greater likelihood of subclinical infection during childhood compared with White populations. Socioeconomic status also influences EBV seroprevalence. Children from lower-income quartiles and those whose parents have lower levels of educational attainment show higher rates of EBV seropositivity than children from the highest-income quartile and those whose parents have attained higher levels of formal education.[8][9]

Pathophysiology

EBV most commonly spreads through close personal contact with an infected individual, particularly through exposure to saliva. Transmission may occur through sharing eating utensils or water bottles, kissing, and sexual intercourse.[10] The incubation period for EBV infection ranges from 32 to 49 days, during which infected individuals remain contagious.[10] Initial viral replication occurs within the oral cavity, although investigators have also isolated EBV from genital secretions. Following introduction into the oropharynx through infected saliva, the virus infects epithelial cells and replicates, demonstrating a particular affinity for B lymphocytes within lymphoid tissue.[10]

The infection subsequently disseminates through the lymphatic system, triggering a cellular immune response characterized by activation of CD4+ and CD8+ T lymphocytes. Resulting lymphoid hyperplasia commonly manifests as generalized lymphadenopathy, tonsillitis, and hepatosplenomegaly. Symptom onset generally occurs after an incubation period of 4 to 8 weeks. After symptoms develop, EBV continues to shed in saliva for 6 to 18 months, although transmissibility reaches its highest level during the symptomatic phase. Salivary transmission remains the primary route of spread, despite the virus not being considered highly contagious. EBV persists within latently infected memory B cells and undergoes periodic reactivation, during which viral shedding recurs in oropharyngeal secretions.

Histopathology

Histopathological signs of EBV include focal or diffuse infiltration by small-to-intermediate atypical lymphocytes, lymphoepithelial lesions, and granulation tissue. Atypical or "reactive" lymphocytes, sometimes referred to as "Downey cells", characteristically have a lobed nucleus surrounded by visible cytoplasm (see Image. Reactive Lymphocytes in Concurrent Leukemia and Mononucleosis). 

History and Physical

Classic symptoms of infectious mononucleosis include the triad of sore throat, lymphadenopathy, and fever. In a case series of 500 individuals with confirmed infectious mononucleosis, over 98% presented with a sore throat, lymphadenopathy, fever, and tonsillar enlargement.[11] In another case series of 150 individuals with infectious mononucleosis, the classic triad of symptoms was less common: 74% presented with sore throat, 57% with lymphadenopathy, and 45% with fever.[12] However, clinical presentation varies by age. Children younger than 5 years frequently develop fever, pharyngitis, and lymphadenopathy but demonstrate a greater likelihood of presenting with rash, palpable splenomegaly, and upper respiratory tract symptoms than adolescents and adults.[10]

Lymphadenopathy most commonly involves the cervical lymph nodes as they drain the pharynx and tonsils, where the EBV first infects epithelial cells and replicates. Lymphadenopathy is typically symmetric and may be tender to palpation. Lymphadenopathy is most common in the first week following the onset of symptoms. Pharyngeal inflammation with tonsillar exudates is common, but may resemble other causes of acute pharyngitis, eg, group A Streptococcus infection.

Additional common manifestations of infectious mononucleosis include splenomegaly, fatigue, headache, rash, myalgias, and arthralgias. Splenomegaly occurs in approximately 50% of affected individuals. The rash associated with infectious mononucleosis typically presents as a generalized, erythematous, maculopapular eruption (see Image. Rash from Infectious Mononucleosis). Among patients with HIV infection, Epstein-Barr virus may contribute to the development of several secondary conditions, including lymphadenopathy, atypical lymphoproliferative disorders, and malignant transformation involving lymphoid, muscle, and epithelial cells.[10]

Evaluation

Clinicians should suspect EBV-associated infectious mononucleosis in patients presenting with fever, cervical lymphadenopathy, pharyngitis, and fatigue, particularly among children, adolescents, and young adults. Symptom development often follows a gradual course. Diagnostic laboratory evaluation remains appropriate for all patients with suspected infectious mononucleosis because accurate diagnosis supports patient counseling regarding the expected disease course and the risk of splenic rupture.

A complete blood count (CBC) commonly demonstrates leukocytosis accompanied by lymphocytosis and atypical lymphocytes. One systematic review reported that lymphocytosis greater than 50% combined with atypical lymphocytes greater than 10% achieved a sensitivity of 99% for infectious mononucleosis.[13] Liver function tests frequently reveal mildly elevated transaminase levels. HIV testing should be performed in all patients with symptoms consistent with infectious mononucleosis. Acute HIV infection may produce a negative HIV antibody/antigen result; therefore, patients with symptoms suggestive of infectious mononucleosis and negative EBV and HIV antibody/antigen testing should undergo HIV RNA testing. When HIV RNA testing is unavailable, repeat HIV antibody/antigen testing after 2 weeks, and consideration of additional testing for alternative etiologies, eg, CMV and toxoplasmosis, remains appropriate.

EBV testing should be obtained in all patients with suspected infectious mononucleosis. EBV-specific antibody testing demonstrates high diagnostic performance, with sensitivity and specificity of approximately 97% and 94%, respectively.[14] Heterophile antibody testing, commonly known as the Monospot test, provides a reasonable alternative due to its lower cost and faster turnaround time. However, heterophile antibody testing demonstrates lower diagnostic accuracy than EBV-specific antibody testing, with sensitivity ranging from 63% to 84% and specificity ranging from 84% to 100%.[14] Positive results also occur less frequently in infants and young children.

Patients with symptoms of infectious mononucleosis who receive a negative result for EBV on heterophile antibody testing should undergo confirmatory evaluation with EBV-specific antibody testing. Additional testing for group A Streptococcus and HIV should also be performed. Negative findings on these studies should prompt further evaluation for other causes of non-EBV mononucleosis syndrome as clinically indicated.

Diagnostic imaging generally does not contribute to routine evaluation and should be reserved for situations involving concern for airway obstruction, splenic rupture, or hemophagocytic lymphohistiocytosis.

Treatment / Management

Management of infectious mononucleosis remains primarily supportive in most patients. Antiviral agents, including acyclovir, do not have an established role in routine treatment. Symptomatic relief may be achieved with acetaminophen or nonsteroidal anti-inflammatory drugs to reduce fever and alleviate pharyngitis. Supportive measures should also include adequate hydration, sufficient rest, and maintenance of appropriate nutritional intake. Routine corticosteroid therapy is generally not recommended due to limited clinical benefit and concerns about immunosuppression.

Patients should receive counseling regarding activity restrictions because of the risk of splenic rupture. Avoidance of strenuous physical activity for 3 weeks following illness onset remains recommended. Individuals who participate in contact sports may resume activity 4 weeks after symptom onset, provided clinical recovery has occurred, and no contraindications exist.

Complicated infectious mononucleosis requires prompt recognition and escalation of care. Patients who develop airway obstruction should be urgently referred to the emergency department for airway management and surgical consultation. In such cases, high-dose corticosteroid therapy may help reduce or prevent further airway compromise. Although uncommon, splenic rupture represents a potentially serious complication of infectious mononucleosis. Management typically involves surgical intervention with splenectomy. Selected patients may qualify for close observation and nonoperative management when clinical circumstances permit.

Differential Diagnosis

The differential diagnosis for infectious mononucleosis includes:

• Group A Streptococcus 
• Arcanobacterium haemolyticum
• Other acute respiratory viruses (eg, adenovirus or enteroviruses)
• CMV
• Acute HIV
• Toxoplasma 
• Human herpesvirus 6 (HHV-6) or human herpesvirus 7 (HHV-7)
• Medications (eg, amoxicillin, ampicillin, minocycline, carbamazepine, phenytoin, dapsone)
• Lymphoma 

Pertinent Studies and Ongoing Trials

As of April 2026, an ongoing clinical trial has been identified. The clinical trial NCT06908096 represents a phase I, single-center, randomized, open-label study evaluating the safety of an adjuvanted EBV gH/gL/gp42-ferritin nanoparticle vaccine, administered with or without a gp350-ferritin nanoparticle.[Clinicaltrial.gov. NCT06908096] The trial also assesses vaccine immunogenicity alongside safety outcomes for these investigational formulations.

Prognosis

Most individuals with infectious mononucleosis recover without sequelae and develop lifelong immunity to EBV. The acute phase of illness typically resolves within 1 to 2 weeks, although fatigue may persist for several months after initial symptom improvement.

Return to normal activity should be guided by the risk of splenic injury as well as functional limitations related to illness-associated fatigue. Infectious mononucleosis is generally self-limited, with symptom duration ranging from 3 days to 8 weeks.[10] In some cases, patients report persistent fatigue lasting 6 months or longer.

Complications

Although rare, the following complications can develop from infectious mononucleosis:

• Upper airway obstruction from massive lymphadenopathy
• Splenic rupture [15]
• Autoimmune hemolytic anemia
• Pancytopenia
• Hemolytic uremic syndrome
• Episcleritis and uveitis
• Erythema multiforme
• Malignancy, including Burkitt lymphoma, Hodgkin lymphoma, and nasopharyngeal carcinoma [16][17]
• Chronic autoimmune disorders, including multiple sclerosis and chronic vascular diseases [17]

Age greater than 30 years can be an isolated risk factor for severe infectious mononucleosis, with those patients having more frequent hepatic, splenic, neurologic, and hematologic complications.[18]

Deterrence and Patient Education

Acute infectious mononucleosis is a self-limited viral illness requiring supportive care, with most individuals recovering within 2 to 3 weeks. Symptoms of fatigue may persist longer, however. The key safety message for individuals with mononucleosis is to avoid contact sports for at least 4 weeks because of the risk of splenic rupture, which occurs in 0.1% to 0.2% of cases, with most ruptures occurring within the first 21 days after symptom onset.[19] Antibiotics are not indicated for the treatment of infectious mononucleosis, and the use of amoxicillin is associated with a characteristic maculopapular rash in up to 30% of individuals.[13] In addition, antiviral therapy is not indicated. 

Pearls and Other Issues

Factors that should be kept in mind when managing infectious mononucleosis include:

• The diagnostic test of choice for infectious mononucleosis is EBV-specific antibody testing, given its high sensitivity and specificity. Heterophile antibody testing (eg, the "Monospot test") is a reasonable alternative to EBV-specific antibody testing given its faster turnaround time and lower expense, but it has a lower sensitivity and specificity than EBV-specific antibody testing.
• The most important entity to exclude from the differential diagnosis is primary HIV infection, but other acute infectious etiologies, eg, CMV, toxoplasmosis, and other viral etiologies (eg, adenovirus) can be considered if the initial diagnostic workup is negative.
• Splenic rupture is a rare complication in infectious mononucleosis but can be potentially life-threatening if not diagnosed in a timely fashion. 

Enhancing Healthcare Team Outcomes

Infectious mononucleosis, most commonly caused by EBV, results from viral infection of oropharyngeal epithelium with B-cell tropism and lymphoproliferative immune response. Transmission occurs via saliva, with incubation of several weeks. Clinical features include fever, pharyngitis, cervical lymphadenopathy, fatigue, and splenomegaly, with possible rash and hepatosplenic involvement. Evaluation relies on lymphocytosis with atypical lymphocytes, mild transaminitis, and confirmation using EBV-specific or heterophile antibody testing, alongside HIV testing to exclude acute infection. Management is primarily supportive, avoiding antiviral therapy, with limited steroid use for complications. Activity restriction is required to reduce the risk of splenic rupture. Complications include airway obstruction, splenic rupture, hematologic abnormalities, and malignancy.

Interprofessional care improves diagnostic accuracy, timely management, and coordinated roles. Physicians and advanced practitioners lead evaluation and treatment decisions, nurses reinforce monitoring and patient education, pharmacists support medication selection and safety, and care teams ensure follow-up, activity counseling, and complication surveillance through shared decision-making and communication.

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Disclosure: Michael Mohseni declares no relevant financial relationships with ineligible companies.

Disclosure: Jeffrey Jenks declares no relevant financial relationships with ineligible companies.