Infectious Period for Measles in Children
Children with measles are contagious from 4 days before the rash appears until 4 days after the rash onset. 1, 2, 3
Detailed Timeline of Contagiousness
The infectious period spans a total of approximately 8-9 days centered around rash onset:
- Pre-rash period (4 days before): Children begin shedding virus during the prodromal phase when they have fever, cough, coryza (runny nose), and conjunctivitis but before the characteristic rash appears 1, 2
- Rash period (4 days after): Contagiousness continues through the first 4 days after the rash emerges 1, 2
- Total infectious window: Approximately 8 days (4 days before + 4 days after rash onset) 1, 2, 3
Critical Clinical Implications
Isolation Requirements
Children diagnosed with measles must be placed under airborne isolation precautions for at least 4 days after rash onset. 1, 2 This requires:
- Negative air-pressure room (airborne-infection isolation room) 1
- N95 respirators for all healthcare staff entering the room, regardless of immunity status 1, 3
- Immediate masking of the patient if airborne isolation room unavailable 1
Contact Management
All exposed contacts without documented immunity must be identified immediately and managed aggressively: 1, 2
- Healthcare workers lacking immunity should be excluded from work days 5-21 after exposure, even if they receive immune globulin prophylaxis 1, 3
- Post-exposure prophylaxis with MMR vaccine is effective if given within 72 hours of exposure 2, 3
- Immune globulin (0.25 mL/kg IM, maximum 15 mL) can prevent or modify infection if given within 6 days of exposure when vaccine is contraindicated 1, 2, 3
Special Populations Requiring Extended Precautions
Immunocompromised Children
Severely immunocompromised children may shed measles virus for several weeks after acute illness and can present without the typical rash. 1, 2 These children require:
- Extended isolation beyond the standard 4-day post-rash period 2
- Serial viral cultures to document clearance 2
- Heightened surveillance for atypical presentations 2, 4
Healthcare Workers
Healthcare workers who develop measles must be excluded from work until at least 4 days following rash onset. 3 The ~1% vaccine failure rate among previously vaccinated healthcare workers necessitates universal airborne precautions when caring for measles patients, regardless of documented immunity 1, 3
Common Pitfalls to Avoid
- Do not wait for rash to implement isolation: The 4-day pre-rash infectious period means children are highly contagious during the prodromal phase when diagnosis may not yet be suspected 1, 2
- Do not assume vaccinated individuals are non-infectious: Primary vaccine failure occurs in up to 5% of single-dose recipients, and breakthrough infections can occur 1
- Do not discharge contacts prematurely: The incubation period averages 10-12 days to prodrome and 14 days to rash (range 7-18 days), so exposed susceptible contacts require monitoring through day 21 1, 2