What are the symptoms and timing of measles after exposure?

Measles Symptoms and Timing After Exposure

Measles is infectious 4 days before rash onset through 4 days after rash onset, with symptoms typically appearing 8-12 days after exposure and progressing through distinct phases. 1

Timeline of Measles After Exposure

Incubation Period

• 8-12 days from exposure to first symptoms
• Range can be 7-21 days
• During this period, the person is asymptomatic but the virus is replicating

Prodromal Phase (2-4 days)

• Classic "3 Cs": Cough, Coryza (runny nose), Conjunctivitis
• High fever (≥38.3°C/≥101°F)
• Malaise and fatigue
• Pathognomonic sign: Koplik spots (small white spots on bright red background inside the mouth) typically appear 1-2 days before the rash 2

Rash Phase

• Characteristic erythematous, maculopapular rash appears around day 14 after exposure
• Rash progression:
  • Begins on face, particularly at the hairline
  • Spreads cephalocaudally (head to toe)
  • Becomes more confluent as it spreads
  • Lasts approximately 3-7 days
  • Fades in the same order it appeared 1, 2

Contagious Period

• Begins 4 days before rash onset
• Continues until 4 days after rash appearance
• Critical point: Patients are most contagious during the late prodromal phase (just before rash appears) 1

Clinical Case Definition

A clinical case of measles is defined as an illness characterized by:

• Generalized rash lasting ≥3 days
• Temperature ≥38.3°C (≥101°F)
• Cough, coryza, or conjunctivitis 1

Complications

Complications occur in 10-40% of patients 2 and may include:

• Otitis media
• Laryngotracheobronchitis
• Pneumonia (primary viral or secondary bacterial)
• Diarrhea
• Stomatitis

Serious neurological complications (uncommon but severe):

• Acute disseminated encephalomyelitis (during or soon after acute disease)
• Measles inclusion body encephalitis (months later)
• Subacute sclerosing panencephalitis (years later) 3

Special Considerations

Modified Measles in Vaccinated Individuals

• Vaccinated individuals may experience milder symptoms or even subclinical infection
• However, transmission from vaccinated individuals with breakthrough infection is possible, though rare 4

Prolonged Incubation

• If immune globulin is administered to an exposed person, the incubation period may be prolonged to 28 days 1

Laboratory Confirmation

For suspected cases, laboratory confirmation is essential:

• Measles IgM antibody testing (may not be detectable until 72 hours after rash onset)
• Measles virus isolation from clinical specimens (urine, nasopharyngeal mucus)
• Collection timing is critical - specimens should be collected as close to rash onset as possible 1

Important Pitfalls to Avoid

1. Don't wait for rash to suspect measles - The prodromal phase is highly contagious
2. Don't rule out measles in vaccinated individuals - Breakthrough infections can occur
3. Don't delay isolation - Implement airborne precautions immediately upon suspicion
4. Don't miss the window for specimen collection - Collect specimens as close to rash onset as possible
5. Don't forget to notify public health authorities - Measles is a reportable disease requiring immediate notification

Remember that measles remains highly contagious and potentially fatal, especially in unvaccinated individuals, young children, and immunocompromised patients.