Infectious mononucleosis

Infectious mononucleosis

Case Presentation

A 16-year-old boy presents to A&E with a fever, an extremely sore throat, and a recent blotchy rash on his back that has been concerning him. He complains of feeling extremely tired and lethargic for the past two weeks. He denies having recently been in contact with anyone ill and confirms that he is up-to-date with his vaccinations. He mentions a visit with his local GP last week, where his doctor prescribed a dose of amoxicillin for a suspected throat infection. He has no other significant medical history. Upon further examination, his pharynx and tonsils appear inflamed with whitewash exudate and he has swollen neck lymph nodes in both the anterior and posterior triangles of the neck.

What is/are the most appropriate next step(s) in the patient’s management?

The answer is c) Arrange a full blood count and a monospot test

What is Glandular Fever?

Infectious mononucleosis, also known as glandular fever, is an infection resulting most commonly (80-90%) from an Epstein-Barr virus (EBV). About 95% of adults in the world have been infected with EBV; however, it is rare for it to progress into glandular fever. Glandular fever is most commonly seen in individuals aged 15-24, but can present in all age groups. The prevalence of glandular fever is estimated to be between 5-48 cases per 1000 persons. Glandular fever is rather rate in those under 10 or older than 30 (1/1000 persons), so it may not need to be in your top differentials in those age groups! In young adults, the likelihood of developing glandular fever from a primary EBV infection is about 50%; in older adults the chances of EBV infection progressing to glandular fever is slim.

For the most part, glandular fever is not contagious. It’s mostly spread through contact with saliva; such as by kissing, sharing food, or children putting things in their mouths. It can also be spread through sexual contact. Luckily, in most occurrences, glandular fever is self-limiting and lasts two to four weeks. The most common lasting effect is fatigue, which can continue from weeks to months.

When Should You Suspect Glandular Fever?

The classic ‘triad’ of symptoms for glandular fever are: 

  • Fever
  • Lymphadenopathy
  • Pharyngitis (‘sore throat’)

Bilateral posterior cervical lymphadenopathy is typical for glandular fever. Tonsils may also be enlarged, and exudate on the tonsils is described as ‘whitewash’. 

Additional signs and symptoms that could include:

  • Prodromal symptoms: 
    • Fatigue, chills, myalgia, headache
  • Palatal petechiae
    • 1-2mm in diameter and lasting 3-4 days
  • Abdominal pains 
  • Nausea and vomiting 
  • Non-specific rash
    • In this case, the patient had a maculopapular rash which is associated with EBV infection. It can be caused by the infection directly but more commonly presents after being treat with amoxicillin; patients should not take penicillin antibiotics when they have infectious mononucleosis. 
  • Splenomegaly 

If you see, or the patient tells you, of any of the following symptoms during their visit to the emergency department, it requires hospitalization! 

  • Difficulty swallowing 
  • Difficulty breathing 
  • Severe stomach/abdominal pain

These may suggest malignancy. Difficulty swallowing and breathing are most often due to inflamed tonsils and may require steroids. Severe stomach/abdominal pain might suggest a ruptured spleen. Refer to your local guidelines for investigation and treatment if these symptoms present. 

Differential Diagnoses

Viral pharyngitis

  • This is the most common alternative diagnoses
  • Viral pharyngitis tends to be more erythematous 
  • Exudate is not common with viral pharyngitis

Bacterial tonsillitis

  • Bacterial tonsillitis is more commonly described as having ‘speckled’ exudate on tonsils, compared to the ‘whitewash’ exudate on tonsils in glandular fever
  • Lymphadenopathy is usually limited to the upper anterior cervical chain, where in glandular fever, lymphadenopathy can be commonly seen in both anterior and posterior triangles

Other differentials could include other causes of lymphadenopathy, such as inflammation/infection, lymphoma, or leukemia. Alternative viral infections should also be considered (e.g. cytomegalovirus, acute toxoplasmosis, acute viral hepatitis, inter alia). 

Investigations If Glandular Fever Is Suspected

In children younger than 12, or a person who is immunocompromised, a blood test for EBV viral serology should be arranged (if the patient has been ill for seven days). 

In individuals older than 12, a full blood count with differential white cell count and a monospot test should be arranged in their second week of illness. Glandular fever is likely if:

  • The monospot test is positive
  • The full blood count has more than 20% atypical lymphocytes 


More than 10% atypical lymphocytes and the lymphocyte count is more than 50% of the total white cell count.


The patient only needs to be hospitalized if they have stridor, difficulty swallowing, are dehydrated, or there is a chance of potentially serious complications (such as a splenic rupture). Steroids should only be used if the patient shows to have difficulty breathing, otherwise, management should be conservative. If the patient doesn’t have any of these concerning signs, it is appropriate to advise the patient of their illness and discharge them for follow-up with their GP.

Some Recommendations To Patients

Some things you can advise the patient on for self-management of glandular fever include:

  • Symptoms usually only last 2-4 weeks 
  • Fatigue may be the last symptom to resolve
  • Relieve symptoms of pain and fever with paracetamol or ibuprofen
  • Encouraging normal daily routines and that exclusion from work or school is not necessary
  • Spreading of disease can be limited by avoiding kissing and not sharing eating utensils
  • They should return to the hospital if they suspect any serious complications (such increased difficulty to breath/swallow, or severe abdominal pain)

References and Further Reading

Cite this article as: Nadine Schottler, Great Britain, "Infectious mononucleosis," in International Emergency Medicine Education Project, August 16, 2021,, date accessed: September 21, 2023

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