GPAtlas🧭 When to suspect
Measles is the most infectious of all respiratory-transmitted diseases, caused by a morbillivirus of the paramyxovirus family. With UK uptake of the measles, mumps and rubella (MMR) vaccine below the level needed to interrupt transmission, it is once again circulating – so 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 a prodrome of fever and malaise plus the 3 Cs – cough, coryza and conjunctivitis – followed by Koplik spots (small white spots on the buccal mucosa) and 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 / 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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