Measles is spread through respiration (contact with fluids from an infected person's nose and mouth, either directly or through aerosol transmission), and is highly contagious - 90% of people without immunity sharing a house with an infected person will catch it.
The incubation period is approximately 10-12 days (during which there are no symptoms). The first symptom is typically a fever, reaching up to 40 degrees Celsius (105 Fahrenheit), with a cough and runny nose, red eyes and hypersensitivity to light following soon after. Small, red, irregular spots with a blue-white centre appear inside the mouth, known as "Koplik's spots", and are one of the primary ways doctors diagnose measles before the characteristic large, red-brownish blotches that form the rash most commonly associated with measles appear. The rash and fever fades gradually over 7 to 10 days, with the last remnants of the rash usually gone by 14 days. Infected people remain contagious from the appearance of the first symptoms until about 4 days after the rash appears.
Complications with measles are relatively common, ranging from relatively common and less serious diarrhea, to pneumonia and encephalitis. Complications are usually more severe amongst infants and adults who catch the virus.
The fatality rate from measles for otherwise healthy people in developed countries is low: approximately 1 death per thousand cases. In underdeveloped nations with high rates of malnutrition and poor healthcare, fatality rates of 10 percent are common. In immunocompromised patients, the fatality rate is approximately 30 percent.
In developed countries, most children are immunised against measles soon after birth as part of a three-part MMR vaccine (measles, mumps, and rubella). Vaccination rates have been high enough to make measles relatively uncommon. Even a single case in a college dorm or similar setting is often met with a local vaccination program, in case any of the people exposed are not already immune. In developing countries, measles remains common.
See also German measles.