Measles, also known as rubeola, is an infection, mainly of the nose, windpipe and lungs that is very contagious, meaning it spreads easily from person to person. The measles virus usually spreads when someone comes into contact with droplets from another person that contain the virus. This can happen when someone with the virus coughs or sneezes. It also can happen when people touch used tissues, share drinking glasses or touch hands that have infected droplets on them.
Once the virus gets into the body, the infection spreads throughout the nose, windpipe and lungs, into the skin and other body organs.
A person with measles can spread the virus to others from one to two days before any symptoms begin (or three to five days before the rash) to four days after the rash appears.
Measles typically causes moderate illness. In younger children, complications include middle ear infection (otitis media), pneumonia, croup and diarrhea. In adults, the illness tends to be even more severe. It is not unusual for older patients to require hospital treatment for measles-related pneumonia.
The most serious consequences of measles are rare. In less than 1 of every 1,000 cases, measles produces encephalitis (brain infection), with an immediate risk of seizures, coma and death, and a long-term risk of mental retardation or epilepsy. Subacute sclerosing panencephalitis is an extraordinarily rare chronic form of measles encephalitis that causes brain damage. In unusual cases, measles also can directly attack the digestive organs (including the liver), the heart muscle or the kidneys. A pregnant woman who is infected with measles has an increased risk of premature labor, miscarriage or delivery of a low-birth-weight infant.
Before an effective vaccine was available, there were at least 400,000 cases of measles reported each year in the United States, with probably more than 3 million unreported cases. Now, the number of cases has decreased by more than 99%. Only 251 cases were reported in the United States between 2001 and 2004, with most involving people who either came from countries where measles is common or had traveled recently to those countries.