Clinical Presentation of Measles
Measles presents with a characteristic prodrome of fever, cough, coryza (runny nose), and conjunctivitis ("the three Cs"), followed by a maculopapular rash that begins on the face and spreads downward to the trunk and extremities. 1
Incubation and Timeline
- The incubation period averages 10-12 days from exposure to prodrome and 14 days from exposure to rash (range: 7-18 days). 1
- Patients are contagious from 4 days before rash onset to 4 days after rash appears, making early recognition critical for infection control. 1, 2
Prodromal Phase (Before Rash)
The prodrome is characterized by:
- High fever (typically 101-104°F or 38.3-40°C) with acute onset 3
- Cough - prominent respiratory symptom 1, 2
- Coryza (runny nose) - distinguishes measles from other exanthems 1, 2
- Conjunctivitis ("pink eye") - bilateral and nonpurulent 1, 2
- Koplik spots - small white spots on a red background on the buccal mucosa, appearing 2-3 days before the rash; these are pathognomonic when present but may be missed if not specifically examined 1, 2, 3
Rash Phase
- The erythematous maculopapular (or morbilliform) rash appears approximately 2-4 days after fever onset 3
- Rash begins on the face and behind the ears, then spreads in a cephalocaudal pattern (downward) to the trunk and out to the extremities 1, 2, 3
- The rash appearance coincides with the peak of symptoms 4
- As the rash evolves, it may become hyperpigmented and can be used as a diagnostic feature in resource-limited settings 5
Key Distinguishing Features
Measles is distinguished from other viral exanthems by:
- Prominent respiratory symptoms (cough, coryza) and conjunctivitis occurring together 3
- Higher fever (≥101°F) compared to rubella (>99°F) 3, 6
- Koplik spots when present (pathognomonic but transient) 1, 2
- Descending rash pattern starting on face, unlike the "slapped cheek" appearance of fifth disease 6
- Severe constitutional symptoms compared to the milder presentation of rubella 3
Common Complications to Monitor
- Diarrhea - most common complication 2
- Otitis media (middle ear infection) 2
- Bronchopneumonia - most lethal complication and leading cause of measles-associated mortality 1, 2, 3
- Encephalitis - occurs in approximately 1 per 1,000 cases and may result in permanent brain damage 1, 2
- Death - occurs in 1-2 per 1,000 reported cases in the United States, primarily from pneumonia and encephalitis 1, 2
High-Risk Populations with Severe Presentations
- Infants and young children have higher mortality risk 2
- Adults experience higher complication rates 2
- Pregnant women may develop premature labor, spontaneous abortion, or deliver low birth weight infants 1, 2
- Immunocompromised individuals (including those with HIV, leukemia, lymphoma) may develop severe, prolonged infection that may occur without the typical rash and can shed virus for weeks 1, 2
Critical Pitfall to Avoid
Do not assume vaccination equals immunity - up to 5% of people who received a single vaccine dose have primary vaccine failure, so measles should remain in the differential diagnosis even in previously vaccinated individuals presenting with compatible symptoms. 1, 3