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). It is spread in saliva – hence the popular name “the kissing disease” – with an incubation period of 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) and lymphadenopathy – characteristically bilateral posterior cervical nodes – 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.
The key primary-care skills are fourfold: recognise it and distinguish it from streptococcal tonsillitis and from sinister mimics; test at the right time (the second week); avoid aminopenicillins; and 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) / 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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