Ask the Experts: MMR (Measles, Mumps, and Rubella): Disease Issues

Measles can lead to serious complications and death, even with modern medical care. The 1989–1991 measles outbreak in the U.S. resulted in more than 55,000 cases and more than 100 deaths. In the United States, from 1987 to 2000, the most commonly reported complications associated with measles infection were pneumonia (6%), otitis media (7%), and diarrhea (8%). For every 1,000 reported measles cases in the United States, approximately one case of encephalitis and one to three deaths resulted. The risk for death from measles or its complications is greater for infants, young children, and adults than for older children and adolescents. In 2025, three people died from complications of measles in the United States: two otherwise healthy, unvaccinated, elementary school-aged children and one adult; 11% of confirmed measles cases were hospitalized in 2025.

Mumps most commonly causes fever and parotitis. Up to 25% of persons with mumps have few or no symptoms. Complications of mumps include orchitis (inflammation of the testicle) and oophoritis (inflammation of the ovary). Other complications of mumps include pancreatitis, deafness, aseptic meningitis, and encephalitis. Mumps illness is typically milder, with fewer complications, in fully vaccinated case patients.

Rubella is generally a mild illness with low-grade fever, lymphadenopathy, and malaise. Up to 50% of rubella virus infections are subclinical. Complications can include thrombocytopenic purpura and encephalitis. Rubella virus is teratogenic and infection in a pregnant woman, especially during the first trimester, can result in miscarriage, stillbirth, and birth defects including cataracts, hearing loss, intellectual disabilities, and congenital heart defects.

Healthcare providers should suspect measles in patients with a febrile rash illness and the clinically compatible symptoms of cough, coryza (runny nose), and/or conjunctivitis (red, watery eyes). The illness begins with a prodrome of fever and malaise a few days before rash onset. A clinical case of measles is defined as an illness characterized by

• a generalized rash lasting 3 or more days, and
• a temperature of 101°F or higher (38.3°C or higher), and
• cough, coryza, and/or conjunctivitis.

Koplik spots, a rash present on mucous membranes, are considered pathognomonic (diagnostic) for measles. Koplik spots occur from 1 to 2 days before the measles rash appears to 1 to 2 days afterward. They appear as punctate blue-white spots on the bright red background of the buccal mucosa. In practice, Koplik spots are not often seen or properly recognized, and their absence should not affect the diagnosis of measles. Pictures of measles rash and Koplik spots can be found at https://www.immunize.org/clinical/image-library/measles/.

Providers should be especially aware of the possibility of measles in people with fever and rash who have recently traveled abroad or to an area with an ongoing outbreak in the United States, or those who have had contact with people from an outbreak area or international travelers. Providers should immediately isolate and report suspected measles cases to their local health department and obtain a nasopharyngeal, throat, and/or urine specimen for diagnosis confirmation and virus genotyping. Providers should also collect blood for serologic testing during the first clinical encounter with a person who has suspected or probable measles.

For measles, there is an average of 10 to 12 days from exposure to the appearance of the first symptom, which is usually fever. The measles rash doesn’t usually appear until approximately 14 days after exposure (range: 7 to 21 days), and the rash typically begins 2 to 4 days after the fever begins. The incubation period of mumps averages 16 to 18 days (range: 12 to 25 days) from exposure to onset of parotitis. The incubation period of rubella is 14 days (range: 12 to 23 days). However, up to half of rubella virus infections cause no symptoms.