Cases of measles have been recorded in at least nine U.S. states since the start of the year, as local health officials attempt to prevent the spread of the disease.

There have been confirmed cases in parts of California, Delaware, Georgia, Pennsylvania, Maryland, Missouri, New Jersey, Ohio and Washington, and officials are investigating whether others who had close contact with those infected may have contracted it as well.

Measles is a highly contagious disease caused by a virus that spreads through an infected person's breath, coughs or sneezes. Symptoms tend to include a cold-like illness and a rash of tiny red spots, but it can cause complications and, in some cases, lead to death.

On February 3, the director of the Ohio Department of Health reported the state's first case of 2024, in a child from Montgomery County, which includes the city of Dayton. It said at the time it wasn't aware of any additional cases, but it was working to identify others who may have been exposed.

On February 1, the Maryland Department of Health confirmed a positive case in a Montgomery County resident who traveled internationally prior to becoming infected.

Officials in the state warned that the person had been at Washington Dulles International Airport on the morning of January 27; Claridge House in Silver Spring that afternoon and on the morning of January 29; and the Suburban Hospital Emergency Department in the evening of January 27. Others in those locations at those times may have been exposed, they said.

Also on February 1, the Los Angeles County Department of Public Health in California announced that a resident had contracted the illness and had traveled through Los Angeles International Airport in the afternoon of January 25.

On January 18, the Georgia Department of Public Health confirmed a case of measles in an unvaccinated resident of the Atlanta area, who was exposed abroad. On January 12, health officials in Clay County, Missouri, also confirmed a case of measles in a Liberty resident, following travel via Kansas City International Airport.

Prior to that, on January 11, the Delaware Division of Public Health announced that 20-30 people may have been exposed to someone who had been at the Nemours Children's Hospital in Wilmington and wasn't showing symptoms of the disease, but was infectious, on December 29, 2023.

On January 13, the Camden County Health Department in New Jersey said it was "closely monitoring" a confirmed case of measles in the area who had visited two nearby health-care facilities earlier in the month.

Health officials in Philadelphia, Pennsylvania, have been tracking an outbreak of measles in the city. As of January 22, there had been nine confirmed cases. One of those cases was in nearby Montgomery County, and health officials said at the time that there had been no new cases recorded in the prior seven days.

Officials in Washington state said that, as of January 6, six epidemiologically connected cases of measles had been identified in Clark and Wahkiakum counties. They stressed that the risk to the public was deemed low and the infections likely occurred in mid- to late December.

Health officials in the U.S. urged people to get the MMR vaccine. One dose is 93 percent effective at preventing measles, while two doses are 97 percent effective.

According to figures compiled by the Centers for Disease Control and Prevention (CDC), as of January 25 this year, there have been nine new cases of measles reported in the U.S., discounting infections that occurred at the end of 2023.

The worst year for measles in the U.S. since 1992 came in 2019, when there were 1,274 cases recorded nationwide.

The disease was declared eliminated in the U.S. in 2000, but America could lose that status if an outbreak of more cases than the CDC expects from international travel were to occur for more than a year.