Differentiating measles from other causes of rash - ED guidance
Introduction
Measles is highly infectious, causes a characteristic prodrome and rash, and requires prompt infection‑control and public‑health action in the emergency department. Rapid recognition limits nosocomial spread, ensures appropriate treatment and triggers timely contact‑tracing and post‑exposure measures (GOV.UK; RCEM; UKHSA).
Quick measles checklist (frontline)
- Prodrome: high fever with cough, coryza (runny nose) and conjunctivitis.
- Koplik’s spots: small white/blue‑white spots on the buccal mucosa - highly suggestive if seen.
- Rash: erythematous maculopapular (morbilliform) rash, usually appears 2-4 days after prodrome onset; classically starts on the face/behind the ears and spreads downwards.
- Infectious period: approximately 4 days before to 4 days after rash onset.
- Immediate ED actions: identify at triage, minimise time in shared areas, place patient in a single side room, use appropriate PPE, and notify the local health protection team / UKHSA.
- Testing (discuss with health protection team): collect oral fluid and serum for serology (IgM/IgG) and PCR from throat/nasopharyngeal swab or urine - collect early to maximise yield.
Key differentials - focused comparisons
Use history and examination to separate causes: timing of rash versus fever (roseola vs measles), lesion morphology (vesicles vs macules vs petechiae), presence of Koplik’s spots, severe pharyngitis/strawberry tongue (scarlet fever), and rapid systemic collapse (meningococcal).