Contagious Period for Measles
A person with measles is contagious from 4 days before the rash appears until 4 days after the rash onset, for a total contagious period of approximately 8-9 days. 1, 2
Infectious Timeline
The contagious period begins during the prodromal phase when patients have fever, cough, coryza, and conjunctivitis but before the characteristic rash develops, making early identification challenging. 1
Pre-rash contagious period: Patients are infectious starting 4 days before rash onset, during which time they may not yet be diagnosed with measles. 1, 2
Post-rash contagious period: Infectivity continues through 4 days after the rash appears, after which transmission risk ends. 1, 2
Peak infectivity: The person is most contagious when the rash first appears, though transmission occurs throughout the entire 8-9 day window. 1
Isolation Requirements
Healthcare workers and other infected individuals must be isolated until at least 4 days after rash onset to prevent transmission. 1, 2
Healthcare personnel who develop measles should be excluded from work until ≥4 days following rash onset. 1, 2
During healthcare visits, patients should immediately wear a medical mask and be placed in an airborne-infection isolation room (negative air-pressure room) as soon as possible. 1, 2
If an airborne-infection isolation room is unavailable, place the patient in a private room with the door closed while wearing a mask. 1, 2
Exposure Management for Contacts
Healthcare workers and other contacts without evidence of immunity who are exposed to measles require specific exclusion periods even if they receive post-exposure prophylaxis. 1
Vaccinated contacts after exposure: Healthcare workers without evidence of immunity should be offered MMR vaccine and excluded from work from day 5 through day 21 following exposure. 1, 2
Unvaccinated contacts: Those who do not receive post-exposure vaccination should be excluded from day 5 after first exposure through day 21 after last exposure, even if they receive immune globulin. 1
Immune globulin recipients: If immune globulin is administered to an exposed person, observation should continue for 28 days after exposure because immune globulin may prolong the incubation period. 1, 2
Critical Pitfalls to Avoid
The most dangerous aspect of measles transmission is the 4-day pre-rash contagious period when patients are infectious but not yet diagnosed. 1, 2
Pre-symptomatic transmission: Patients are already contagious during the prodromal phase with nonspecific symptoms (fever, cough, coryza, conjunctivitis) before the diagnostic rash appears, allowing unrecognized transmission. 1, 2
Premature discontinuation of isolation: Do not discontinue isolation before the full 4 days after rash onset have elapsed, as this is a common error that perpetuates transmission. 2
Inadequate respiratory protection: Regular surgical masks are insufficient; all staff entering the room of a patient with suspected or confirmed measles must use N95 respirators or equivalent respiratory protection, regardless of immunity status. 1, 2
Failure to implement airborne precautions immediately: Airborne infection-control precautions must be followed stringently as soon as measles is suspected, not after confirmation. 1, 2
Special Circumstances
In outbreak settings, exclusion periods may be extended for unvaccinated individuals who refuse vaccination. 1
During outbreaks in schools or daycare facilities, persons exempted from vaccination or who refuse vaccination should be excluded until 21 days after the onset of rash in the last case of measles. 1
For healthcare facility outbreaks, exposed susceptible workers should be excluded from the 12th day after first exposure through the 26th day after last exposure if specific outbreak protocols are implemented. 2