A cardiologist at Children’s Hospital of Philadelphia’s campus in King of Prussia has tested positive for the new coronavirus and was in critical condition at the Hospital of the University of Pennsylvania, health officials said Monday.

The doctor, who recently had traveled to another country where the virus is circulating, is one of seven Montgomery County residents who have tested positive for the virus at a state laboratory, county officials said in a Monday afternoon news conference.

CHOP is contacting patient families who may have come into contact with the doctor over the last week and is advising them to self-quarantine, hospital executive officer Madeline Bell said in a Monday email to CHOP staff obtained by The Inquirer.

Asked how many families met that description and how sick their children are, a hospital spokeswoman declined to answer. Children with complex heart problems can be medically fragile, and much more vulnerable to infections than other children.

At the county news conference, Valerie Arkoosh, a physician and chair of the Montgomery County Board of Commissioners, said she had been told that 13 patients who live in the county “had direct contact” with the infected cardiologist.

Contacts led officials in six school districts to close area schools for cleaning.

CHOP officials declined to say how many employees at the King of Prussia location may have been exposed. Staff who came into contact with the doctor have also been instructed to self-quarantine at home for two weeks, according to the staff email.

As of Monday morning, the hospital had suspended its cardiology services and adjacent allergy clinics in King of Prussia, and was redirecting patients who are normally treated there to the hospital’s main Philadelphia campus. Montgomery County health officials were in the process of identifying anyone the man came in contact with since becoming infected.

The cardiologist, an Upper Merion resident, initially was taken by ambulance to Paoli Hospital early Saturday morning, according to township officials. He later was transferred to the Hospital of the University of Pennsylvania in Philadelphia.

The patient’s critical status was announced by the state Department of Health.

“While we are keeping the physician in our thoughts and hope for his full recovery, we have immediately shifted focus to the well-being of our patients, families and staff who may have been directly or indirectly exposed at this KOP site,” Bell wrote in her email to CHOP employees.

Any patients, family members or staff who show symptoms of coronavirus will be offered testing through the state, Bell said in the email.

The Hospital of the University of Pennsylvania is “using all precautions recommended by the U.S. Centers for Disease Control and Prevention,” Patrick Norton, vice president for public affairs, said in a statement to the media. “This includes care in an isolation room, which is designed for both optimal medical care of patients with infectious diseases and the protection of staff and other patients.”

Six districts announced they would close and clean schools on Tuesday because their students and staff had visited the CHOP facility.

Lower Merion, where district officials said two students and a staff member may have been exposed to coronavirus during visits to the facility, said it would close all schools “for additional sanitizing."

In a message to parents, superintendent Robert Copeland wrote that schools would close out of an “abundance of caution” — a message repeated by other area districts.

The Upper Merion and Norristown districts closed all of their schools Tuesday after learning that students may have been exposed to coronavirus at CHOP, while the Hatboro-Horsham School District, also in Montgomery County, announced it would close Simmons Elementary School.

In Bucks County, Neshaminy High School closed for cleaning because a student was in direct contact with the CHOP specialist. Superintendent Joseph Jones III told parents in a letter that the student and two family members had been asked by the Bucks County Health Department to quarantine at their home.

West Chester’s Henderson High was also to close Tuesday for cleaning. “We received notification today that a Henderson High School student was exposed at a health-care office in King of Prussia on March 5 to a person who tested positive for the coronavirus," district Superintendent Jim Scanlon said.

In King of Prussia, several businesses near the CHOP campus said they had received no notification from health officials that anyone who had been in contact with a coronavirus patient had been on their premises.

Staff writers Maddie Hanna and Sam Wood contributed to this article.