EBV / Infectious Mononucleosis (incl. Amoxicillin Rash)

Condition

Caused by herpesvirus 4 (EBV), spread via saliva (sharing a glass, kissing); incubation 1–2 months. Affects young adults aged 15–25.

Clinical features

Classic triad: fever + enlarged lymph nodes + sore throat. Also: malaise, nausea/vomiting, arthritis in one or more joints, abdominal pain (from splenomegaly/hepatitis), conjunctivitis/uveitis. A faint, widespread, non-itchy rash occurs in ~10% of non-hospitalised patients, lasting about a week.

Amoxicillin/ampicillin rash: a distinct, more intense, itchy maculopapular/morbilliform rash appears on extensor surfaces and pressure points 7–10 days after treatment with a beta-lactam (ampicillin, amoxicillin, or a cephalosporin) — this is a hypersensitivity reaction, not a true allergy, and will not recur on re-exposure to the antibiotic in the absence of EBV.

Investigations

Monospot test, EBV serology, LFTs.

Management

Symptomatic; recovery can take several weeks to months.