When Measles Is No Longer Contagious
Measles is no longer contagious 4 days after the rash appears. 1, 2
Contagious Period
The infectious period for measles extends from 4 days before rash onset through 4 days after rash onset. 1, 2 This 8-day window represents the complete period during which infected individuals can transmit the virus to susceptible contacts.
Key Timeline Points:
- Contagious begins: 4 days before the rash appears 1, 2
- Contagious ends: 4 days after the rash appears 1, 2
- Total infectious period: 8 days 1, 2
Isolation Requirements
General Population
Patients with measles should remain isolated until at least 4 days after rash onset. 2 This means isolation can be discontinued on day 5 after the rash first appeared. 2
Healthcare Workers
Healthcare workers who develop measles must be excluded from work until ≥4 days following rash onset. 1, 2 They may return to work on the 5th day after their rash began. 1
Exposed Individuals Without Immunity
Exposed healthcare workers without evidence of immunity who receive post-exposure MMR vaccine should be excluded from work from day 5 through day 21 after exposure. 1, 2 Those who do not receive vaccine should be excluded from day 5 after first exposure through day 21 after last exposure, even if they receive immune globulin. 1
Critical Pitfalls to Avoid
Pre-Rash Contagiousness
The most dangerous period for transmission occurs during the 4 days before the rash appears, when patients are highly contagious but the diagnosis has not yet been made. 1, 2 During this prodromal phase, patients experience fever, cough, runny nose, and conjunctivitis but lack the characteristic rash. 1
Premature Discontinuation of Isolation
Do not discontinue isolation before the full 4 days after rash onset have elapsed. 2 Ending isolation too early—even by 1-2 days—can result in ongoing transmission to susceptible individuals. 1, 2
Inadequate Airborne Precautions
Standard surgical masks are insufficient for measles. 1, 2 All staff entering the room of a patient with suspected or confirmed measles must use N95 respirators or equivalent respiratory protection, regardless of their immunity status. 1, 2
Special Circumstances
Immune Globulin Administration
If immune globulin is administered to an exposed person, the incubation period may be prolonged. 1 Observation should continue for 28 days after exposure rather than the standard 21 days. 1, 2
Outbreak Settings
During outbreaks in schools or educational institutions, susceptible individuals who are exempt from vaccination should be excluded until 21 days after rash onset in the last case. 1, 2 For healthcare facility outbreaks, exposed susceptible workers should be excluded from the 12th day after first exposure through the 26th day after last exposure. 2