GPAtlas🧭 When to suspect
Infectious mononucleosis (IM), commonly called glandular fever, is an acute, usually self-limiting viral illness caused in the great majority of cases by the Epstein–Barr virus (EBV, also known as human herpesvirus 4).
• The virus is spread in saliva – hence the popular name “the kissing disease”.
• The incubation period is 4–8 weeks.
Suspect it in an adolescent or young adult (peak 15–24 years) presenting with the classic triad of:
• Fever
• A severe sore throat (often with tonsillar exudate)
• Lymphadenopathy – characteristically bilateral posterior cervical nodes
The triad is accompanied by profound fatigue. The acute illness usually settles within 2–4 weeks, although tiredness can linger for months.
Over 90% of adults are EBV-seropositive, and most childhood infection is silent.
In practice:
• Recognise it and distinguish it from streptococcal tonsillitis and from sinister mimics
• Test at the right time (the second week)
• Avoid aminopenicillins
• Safety-net for the two emergencies – splenic rupture and airway obstruction
| Consider instead/alongside | Discriminating clues |
|---|---|
| Streptococcal (group A) tonsillitis | • Anterior cervical nodes, no marked fatigue or splenomegaly • FeverPAIN/Centor scores guide antibiotics – but it can co-exist with IM |
| Acute HIV seroconversion | • Fever, rash, lymphadenopathy and mucosal ulcers • Always consider and offer a human immunodeficiency virus (HIV) test if risk factors or a heterophile-negative picture |
| Cytomegalovirus (CMV) or toxoplasmosis | • A mononucleosis-like illness that is typically heterophile-negative • Milder pharyngitis • Relevant in pregnancy or immunosuppression |
| Acute viral hepatitis | Jaundice with markedly deranged liver enzymes. |
| Haematological malignancy (leukaemia/lymphoma) | The “don’t miss” – persistent lymphadenopathy, weight loss, night sweats, or a very abnormal blood count that does not resolve. |
Source: NICE
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