Key Facts

Measles is one of the most contagious infectious diseases known. Despite effective vaccination, outbreaks continue to occur in under-vaccinated populations. It remains a leading cause of vaccine-preventable death in children globally.

Epidemiology

• Global: ~9 million cases/year; ~128,000 deaths/year (WHO 2023)
• UK: largely eliminated but periodic outbreaks in under-vaccinated communities
• 2023–2024: significant UK outbreak with >1,000 confirmed cases (primarily unvaccinated children)
• UK MMR uptake: ~85% first dose (below 95% herd immunity threshold)
• Most deaths in children <5 years and immunocompromised

Aetiology

• Measles morbillivirus (family Paramyxoviridae, genus Morbillivirus)
• Single-stranded RNA virus; only one serotype (vaccine highly effective)
• Transmission: airborne (droplet nuclei) — can remain airborne for 2 hours in enclosed spaces
• Incubation: 10–14 days (to rash onset)

Pathophysiology

• Virus enters via respiratory epithelium → replicates in lymphoid tissue → viraemia → widespread dissemination
• Infects dendritic cells, macrophages, T and B lymphocytes → transient but profound immunosuppression (immune amnesia lasting weeks to months)
• Endothelial infection → Warthin-Finkeldey giant cells in lymphoid tissue
• Rash: immune-mediated (T-cell response to infected endothelial cells) — immunocompromised patients may not develop rash
• Complications arise from immunosuppression (secondary bacterial infection) or direct viral damage (encephalitis)

Prodromal Phase (2–4 days)

• High fever (often >40°C)
• Cough (dry), coryza, conjunctivitis (the 3 Cs)
• Koplik spots: bluish-white spots on erythematous buccal mucosa (opposite molars) — pathognomonic, appear 1–2 days before rash
• Malaise, irritability

Exanthem Phase

• Maculopapular rash: starts behind ears and hairline → face → trunk → extremities (cephalocaudal spread)
• Rash becomes confluent, may desquamate
• Fever peaks with rash onset then resolves
• Lymphadenopathy

Complications

• Otitis media: ~7% (most common complication)
• Pneumonia: ~6% (leading cause of measles death)
• Febrile seizures: ~1%
• Encephalitis: ~0.1% (1 in 1,000 cases) — 15% mortality, 25% permanent brain damage
• SSPE: ~1 in 25,000 — occurs 7–10 years post-infection; fatal progressive neurological deterioration

Red Flags

• Respiratory distress (pneumonia)
• Altered consciousness (encephalitis)
• Immunocompromised patient (severe/prolonged disease, absence of rash)
• Pregnancy (increased maternal mortality, preterm delivery)
• Infants <12 months (too young for vaccination)

Bedside

• Clinical diagnosis: prodrome + Koplik spots + characteristic rash is usually sufficient
• Observations: temperature, SpO2

Bloods

• Measles IgM: positive from rash onset (send within 5 days of rash for UKHSA confirmation)
• Oral fluid swab (salivary IgM): preferred sample for UKHSA confirmation in UK
• Measles RNA PCR: throat swab, nasopharyngeal swab, or urine — for genotyping and confirmation
• FBC: leucopenia, lymphopenia (characteristic)
• LFTs: transaminitis in complicated cases

Imaging

• CXR: if pneumonia suspected (interstitial infiltrates or secondary bacterial consolidation)
• CT head: if encephalitis suspected

Special Tests

• Lumbar puncture: if encephalitis — lymphocytic CSF, elevated protein, measles PCR/IgM in CSF
• UKHSA notification: mandatory notification on clinical suspicion; send confirmation samples

Non-pharmacological

• Isolation: airborne precautions; infectious from 4 days before to 4 days after rash onset
• Supportive care: rest, fluids, antipyretics (paracetamol)
• Notification: immediately notify local health protection team on clinical suspicion
• Contact tracing: identify susceptible contacts; offer MMR within 72 hours of exposure (post-exposure prophylaxis)

Pharmacological

• Vitamin A: WHO recommends for all children with measles — 200,000 IU for age >12 months (50,000 IU for 6–11 months) for 2 consecutive days
• Antibiotics: only for secondary bacterial complications (otitis media, pneumonia)
• Human normal immunoglobulin (HNIG): post-exposure prophylaxis for immunocompromised, pregnant, or infants <6 months if exposed — within 6 days of exposure
• Ribavirin: considered in severe/immunocompromised cases (evidence limited)

Post-exposure prophylaxis:

• MMR vaccine within 72 hours of exposure: for unvaccinated contacts aged ≥6 months
• HNIG: for immunocompromised, pregnant, infants <6 months who cannot receive MMR

Surgical/Interventional

• Not applicable

Referral Criteria

• Hospital admission: pneumonia, encephalitis, immunocompromised, severe dehydration, pregnancy
• Public health: all cases (statutory notification)
• Paediatrics: infants, complicated cases

• Uncomplicated measles: full recovery in 7–10 days
• Overall case-fatality rate: 0.1–0.3% in developed countries; up to 5–10% in developing countries
• Pneumonia: leading cause of measles death (~60% of fatalities)
• Encephalitis: 15% mortality, 25% permanent neurological sequelae
• SSPE: universally fatal (onset 7–10 years post-infection)
• Immunocompromised patients: mortality up to 30%
• Measles in pregnancy: increased risk of spontaneous abortion, preterm birth, maternal pneumonia
• Immune amnesia: measles infection resets immune memory — increased susceptibility to other infections for months

UK MMR Vaccination Schedule

Measles Complications by Frequency