Measles exposures in Montgomery County, Pennsylvania, and Wilmington, Delaware: What to know.

Health officials in counties outside of Philadelphia warned residents this week of measles exposures in their local health facilities from an outbreak in Philadelphia.

Philadelphia residents who were sick with measles have visited health care providers in Montgomery County, Pa., and Wilmington, Del. since late December. State and county health officials are now reaching out to potentially exposed individuals.

There are currently no new cases outside of Philadelphia, where the outbreak has grown to eight confirmed infections. People who are vaccinated against measles or otherwise immune are not at risk of exposure, the Philadelphia Department of Public Health said. People with known exposures who are not vaccinated or otherwise immune should quarantine for 21 days.

» READ MORE: Two more day-care children are infected with the measles. Here’s what to know about the outbreak in Philadelphia.

The outbreak began last month with the hospitalization of an infant at the Children’s Hospital of Philadelphia after travel from a country where the virus is more common. Three other people were infected at CHOP: an infant who was too young to get vaccinated, an unvaccinated older child, and the older child’s unvaccinated parent.

Before Christmas, one of the children with measles violated quarantine guidelines and attended the Multicultural Education Station Day Care at 6919 Castor Ave. in Northeast Philadelphia. Since then, four other children at that day-care center have been diagnosed with the disease.

There have been no known infections outside of CHOP and the day care center.

A Philadelphia resident who was exposed to measles visited two health care facilities in Montgomery County on Jan. 3, the county said Thursday. The time and place of the visits were:

The county’s Office of Public Health is attempting to contact people who were potentially exposed in these locations and confirm their vaccination status.

Montco residents can find more information on measles and follow updates from county health authorities by visiting this website.

An unvaccinated Philadelphia resident visited a health facility in Delaware late last month while infectious, the state’s Division of Public Health announced Monday.

The visit occurred on Dec. 29 and the health facility was Nemours Children’s Hospital in Wilmington, hospital officials told The Inquirer. The exposure occurred a week before the patient tested positive for measles.

Delaware health authorities are contacting people who may have been exposed. They also are recommending that all people who haven’t received both doses of the MMR vaccines — which protects also against mumps and rubella — get vaccinated.

Measles is highly infectious and spreads through breathing in an airborne virus or touching contaminated surfaces, according to the U.S. Centers for Disease Control and Prevention. By some measures, measles is seven times more contagious than COVID-19.

The illness can be dangerous, especially for children under 5, pregnant people, and those with weakened immune systems.

A measles infection can lead to respiratory failure, inflammation of the brain, and death. In rare cases, the virus can cause a yearslong decline of the brain that results in death.

» READ MORE: Health department warns of measles cluster among unvaccinated residents that originated with CHOP patient

Measles symptoms appear up to two weeks after an exposure, according to the CDC. Initially, measles presents like a regular flulike illness: Patients may have a high fever, runny nose, and red, watery eyes. Three to five days after symptoms begin, the rash commonly associated with measles breaks out.

The MMR vaccine offers strong protection.

Even just one dose of the vaccine, which babies can receive when they are 12 months old, is 93% effective at preventing measles, according to the CDC. Two doses bring up that rate to 97%.

People who were born before 1957 or have had measles are also considered immune.