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Mononucleosis in Adult
Other Resources UpToDate PubMed

Mononucleosis in Adult

Contributors: Art Papier MD, William Van Stoecker MD
Other Resources UpToDate PubMed


Infectious mononucleosis is caused by Epstein-Barr virus (EBV), a member of the human herpesvirus family. A prodromal period of 3-5 days includes headache, malaise, myalgia, and fatigue. In adults, fever to 39°C (102.2°F) may persist for 7-10 days or longer in severe cases, with 80%-95% of people reporting some fever.

The classic clinical triad consists of fever, pharyngitis, and cervical adenopathy. Malaise, sweats, sore throat, anorexia, nausea, and headache are the most common symptoms. Myalgias, ocular muscle pain, chest pain, and rhinitis are not infrequent. Photophobia and arthralgias may also occur. The patient appears generally ill with readily apparent cervical adenopathy in most cases. Splenomegaly typically occurs during the second and third week. Hepatomegaly rarely develops.

The classic mononucleosis syndrome occurs almost without exception in teenagers and young adults.

Patients treated with ampicillin or penicillins often develop an exanthematous rash one week following initiation of therapy.

Splenic rupture, which is rare, may be fatal. Other rare complications include upper airway obstruction, hemolytic anemia, thrombocytopenic purpura, severe granulocytopenia, pneumonia, meningoencephalitis, recurrent aseptic meningitis (Mollaret's meningitis), Guillain-Barré syndrome, Miller Fisher syndrome (bilateral ptosis, total ophthalmoplegia, cerebellar symptoms and hyporeflexia), psychosis, Bell palsy, myocarditis, pericarditis, coronary artery spasm, pancreatitis, nephritis, and fulminating hepatic necrosis. Neurological complications, airway obstruction, and splenic rupture are the most common causes of death in otherwise healthy persons. Gastrointestinal symptoms, palatal petechiae, and insidious onset are associated with a prolonged recovery period. Occasionally, jaundice, arthritis, and pneumonitis are seen.


B27.90 – Infectious mononucleosis, unspecified without complication

271558008 – Infectious mononucleosis

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Last Updated:09/21/2021
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Patient Information for Mononucleosis in Adult
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Mononucleosis, often referred to as mono or the "kissing disease," is a contagious infection caused by the Epstein-Barr virus (EBV). This virus is often spread through the saliva or spit, but it can also infect a person who was coughed on or sneezed on, or a person who shared utensils with someone with mono.

In the United States, up to 95% of adults have previously been infected with EBV. Infection in children usually does not make them sick. Fortunately, even though this is a contagious disease, most people become immune to infection.

There has been no vaccine developed to prevent mononucleosis.

Who’s At Risk

Mononucleosis is mostly a disease of teenagers and young adults (peak age is 16), but it can occur at any age.

Signs & Symptoms

It takes between 4 and 8 weeks for symptoms of mononucleosis to appear. The first symptoms, which last from 1 to 3 days, are fatigue, generally feeling ill, and loss of hunger.

The most common symptoms include:
  • Sore throat
  • Fever
  • Swollen lymph nodes
  • Swollen tonsils
  • Skin rash
  • Swollen spleen

The spleen is in the upper left region of the abdomen, to the left of the stomach, and becomes swollen in about 50% of patients with mono.

A less common complication of mono is liver disease, such as hepatitis (inflammation of liver) and jaundice (yellow skin and whites of eyes). Other less common complications are anemia (decrease in red blood cells), heart problems, complications involving the nervous system, and low platelet count in the blood.

Mononucleosis can cause serious illness in people who may have a weakened immune system from HIV / AIDS or in people taking medications that weaken the immune response (eg, after an organ transplant).

Self-Care Guidelines

Since mononucleosis is a virus, it takes time to get better. Sleeping is extremely important, as well as avoiding vigorous sports or any type of physical activity for 2-3 months. To avoid rupturing the spleen, patients should avoid heavy lifting, contact sports, and any other vigorous activities.

Drinking plenty of water and juices will help relieve fever, prevent dehydration, and soothe a sore throat. Gargling salt water (8 ounces of warm water with one-half teaspoon of salt) several times daily can also help soothe a sore throat.

Over-the-counter pain relievers such as ibuprofen (Advil, Motrin) and acetaminophen (Tylenol) can help both fever and body aches.

When to Seek Medical Care

If a healthy diet and rest do not ease symptoms within a 1-2 weeks, or if symptoms come back, seek medical care.


Your doctor will check for swollen lymph nodes, tonsils, or spleen, and will decide the treatment based on your symptoms. However, in most cases, this viral illness resolves with time. Treatment is only directed toward the relief of symptoms.

Acetaminophen (Tylenol) is typically used for fever, headache, or body aches.

Sore throat is usually the worst during the first week of illness and will subside within 2 weeks. Oral corticosteroids such as prednisone are usually given for severe swelling of the throat and tonsils. Sometimes strep throat also occurs with mono and is treated with antibiotics. Ampicillin and amoxicillin are the two medications that should be avoided because these antibiotics will cause a severe rash in patients with mono.

Fatigue may last for months following mono. Contact sports and vigorous activity should be avoided for 2-3 months after mono to avoid damaging the swollen spleen.


Epstein-Barr virus and infectious mononucleosis. Centers for Disease Control and Prevention website. Updated May 16, 2006. Accessed April 14, 2013.

Infectious mononucleosis. The Merck Manuals: The Merck Manual for Healthcare Professionals website. Updated February 2012. Accessed April 14, 2013.

Luzuriaga K, Sullivan JL. Infectious mononucleosis. N Engl J Med. 2010;362(21):1993-2000.

McPhee S, Papadakis M, Rabow MW. Current Medical Diagnosis and Treatment. 51st ed. New York: NY: McGraw-Hill;2012.
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Mononucleosis in Adult
A medical illustration showing key findings of Mononucleosis : Cervical lymphadenopathy, Fever, Headache, Rash, Lymphadenopathy, Pharyngitis, Splenomegaly
Clinical image of Mononucleosis - imageId=419578. Click to open in gallery.  caption: 'Diffuse deeply erythematous patches and thin plaques on the dorsal hand and fingers.'
Diffuse deeply erythematous patches and thin plaques on the dorsal hand and fingers.
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