🧭 When to suspect

Measles is the most infectious of all respiratory-transmitted diseases, caused by a morbillivirus of the paramyxovirus family.

• UK uptake of the measles, mumps and rubella (MMR) vaccine is below the level needed to interrupt transmission, so measles is once again circulating.

• A high index of suspicion is essential in any unvaccinated or under-vaccinated person with a febrile illness and rash.

Suspect measles in a person with this sequence:

• Prodrome: fever and malaise plus the 3 Cs – cough, coryza and conjunctivitis.

• Then Koplik spots (small white spots on the buccal mucosa).

• Then a maculopapular rash that begins on the face and behind the ears and spreads down the body, becoming confluent.

The diagnosis is clinical: isolation and notification must never wait for the laboratory.

The three clinical priorities in primary care are to recognise it, to notify the Health Protection Team (HPT) on suspicion, and to protect vulnerable contacts (infants, pregnant women and the immunocompromised) within the post-exposure window.

Phase	Timing	Key features
Incubation	Typically 10–12 days (range 7–21) from exposure	Asymptomatic.
Prodrome	2–4 days before the rash	• Fever (often high), malaise and the 3 Cs • Koplik spots appear late in the prodrome
Exanthem (rash)	From day 3–5 of illness	• Maculopapular rash starting on the face or behind the ears, spreading downwards and becoming confluent • Fever peaks as the rash appears
Recovery	Rash fades over ~1 week	• Rash fades in order of appearance • Infectious until 4 full days after rash onset

Always consider the differential before attributing a febrile rash to measles: scarlet fever (group A streptococcus), meningococcal disease, Kawasaki disease and other viral exanthems (rubella, parvovirus B19, roseola, enterovirus) can mimic it and some demand specific urgent action.

Source: UKHSA National measles guidelines · NHS England measles guidance

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