Measles is a highly contagious disease that can spread through the air when a person breathes, coughs or sneezes. It is preventable through a safe and effective vaccine – the MMR shot that provides immunity to measles, mumps and rubella – and health officials said in 2000 that the virus had been eliminated in the United States.

The health department said there may have been exposures at Dulles’s international arrivals area and a Howard County pediatric emergency department.