Health officials in Washington said on Feb. 8 that attendees of the March for Life in January may have been exposed to the measles virus.

District of Columbia health officials said in a statement that they were told of “multiple confirmed cases of measles whose carriers visited multiple locations in the District while contagious” and that people who visited several locations between Jan. 21 and Jan. 25 may have been exposed.

These include the March for Life, which took place on Jan. 23 on the National Mall, attended by thousands of pro-life advocates.

Other locations where people could have been exposed include the Basilica of the National Shrine of the Immaculate Conception at the Catholic University of America on Jan. 21, and some other locations on that campus on Jan. 24 and Jan. 25; Reagan Washington National Airport on Jan. 26; several metro Washington trains on Jan. 26 and Jan. 27; and the Amtrak concourse at the city’s Union Station on Jan. 27, officials said.

Measles is a highly contagious virus that can spread easily through the air when an infected individual coughs, sneezes, or breathes, and symptoms generally appear in two distinct stages. The first stage includes a fever, a cough, watery and red eyes, and a runny nose, and it occurs about seven to 14 days after exposure.

In the second stage, a telltale rash starts to appear on the face three to five days after the initial symptoms start. The rash can then spread to the rest of the body.

People who might have been exposed and are not immune should contact their health care provider or the DC Health agency at 844-493-2652, according to the office. People who haven’t received a measles, mumps, and rubella vaccine or another vaccine against measles could be at risk of contracting the virus, the agency said. People who were exposed should watch for symptoms for 21 days after the potential exposure.

Individuals who are infected are contagious from four days before the rash starts to appear to four days after the rash shows up, officials said.

“If you notice the symptoms of measles, immediately isolate yourself by staying home and away from others.” DC Health stated. “Contact your healthcare provider immediately. Call ahead before going to your healthcare provider’s office or the emergency room to notify them that you may have been exposed to measles and ask them to call the health department to help protect other patients and staff.”

Health care officials also should keep “an increased index of suspicion for measles” in the District, it said, “especially if patients were recently exposed.”

The Centers for Disease Control and Prevention had reported 733 confirmed measles cases across the United States as of Feb. 5. Separately, an updated CDC map shows that 546 cases, a majority of measles cases this year, have occurred in South Carolina.

Other states with significant numbers of cases include Utah, which has had 72 so far this year; Arizona, which has reported 25; and Washington, which has reported 16.

A hospital system in South Carolina last week announced that it would impose a mask mandate because of the increase in measles cases in the state.