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

In 2022, a provisional total of 121 cases of measles from 6 states were reported to CDC. The sharply limited global travel and social interactions precipitated by the COVID-19 pandemic, which began in early 2020, also reduced the opportunities for introduction and transmission of measles, mumps, and rubella viruses in the United States. Current CDC measles surveillance updates can be found at www.cdc.gov/measles/data-research/.

Since the pre-vaccine era, there has been a more than 99% decrease in mumps cases in the United States. However, outbreaks still occasionally occur. In 2006, there was an outbreak affecting more than 6,584 people in the United States, with many cases occurring on college campuses. In 2009, an outbreak started in close-knit religious communities and schools in the Northeast, resulting in more than 3,000 cases. Since 2015, numerous outbreaks have been reported across the US, in college campuses, prisons, and close-knit communities, including a large outbreak in northwest Arkansas where almost 3,000 cases were reported in 2016. These outbreaks have shown that when people with mumps have close contact with a lot of other people (such as among residential college students and families in close-knit communities) mumps can spread, even among vaccinated people. However, outbreaks are much larger in areas where vaccine coverage rates are lower. A provisional total of 322 cases of mumps were reported to CDC in 2022.

Rubella was declared eliminated (the absence of endemic transmission for 12 months or more) from the United States in 2004. Fewer than 10 cases (primarily import-related) have been reported annually in the United States since elimination was declared. Rubella incidence in the United States has decreased by more than 99% from the pre-vaccine era. A provisional total of 3 cases of rubella, and no cases of congenital rubella syndrome, were reported in 2022.

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 two 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.

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, mental retardation, 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 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 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. Pictures of measles rash and Koplik spots can be found at 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 who have had contact with international travelers.  Providers should immediately isolate and report suspected measles cases to their local health department and obtain specimens for measles testing, including viral specimens for confirmation and 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, as noted above, up to half of rubella virus infections cause no symptoms.