Correction: In an earlier version of this story, Sen. Chris Van Hollen was quoted as saying that Maryland had received $500 million from the Centers for Disease Control and Prevention. His office later said he misspoke, and that the state had received $500,000.

The three Maryland residents who have tested positive for coronavirus potentially exposed elderly people and children to the infection, prompting the temporary closure of five schools in Bucks County, Pa., and warnings to a Rockville, Md., retirement community to monitor residents for symptoms.

Gov. Larry Hogan said Friday evening that the three people — a husband and wife in their 70s and an unrelated woman in her 50s — contracted the virus while on a Nile River cruise in Egypt.

The World Health Organization and Egypt’s Health Ministry announced that 12 coronavirus cases had originated among workers on the cruise ship. Eight people in the Houston area also reportedly developed covid-19, caused by the virus, after returning to the United States following a Nile cruise. Hogan (R) said the Texas and Maryland cases appeared related.

Five family members of the confirmed Maryland patients have been identified for testing but have not yet been tested, officials said. A broad search for other people who were in contact with the patients and should be tested is underway.

“We are providing these updates not to unnecessarily raise alarm but in the interest of full transparency and out of an abundance of caution,” Hogan said at a news conference. “We are committed to do everything in our power to contain this virus and to limit its spread in our state.”

Although the three residents, all from Montgomery County, had flu-like symptoms after their trip, they were not tested for the virus for nearly two weeks, because at the time of their return, the Centers for Disease Control and Prevention recommended tests only for people who had been traveling in China, Montgomery County Health Officer Travis Gayles said. The residents’ names are being withheld by state officials for privacy reasons.

In the days before they were tested, one of the three attended a private gathering at a residence in Bucks County, according to a statement on the school district’s website. Multiple children and school system staff were there.

The school district closed five schools “for at least one day” as a result, the statement said, and the Bucks County Department of Health was working to contact everyone who attended the gathering and to check them for symptoms of illness. A “small number of people” who were at the gathering and experienced flu-like symptoms have tested negative for covid-19, the school district said. The 14-day incubation period ends Monday.

Another of the Montgomery County residents who tested positive went to The Village at Rockville on Feb. 28 to pay a condolence call to the family of a former resident of the retirement community.

The man’s grandson said between 70 and 100 people attended the event, which in Jewish tradition is known as sitting shiva. Most were family and friends who do not live at the complex, which marketing director Allison Combs said houses about 300 people split among independent living, assisted living and skilled nursing homes.

Hogan called the interactions “concerning” and said anyone who was at the shiva should contact health officials and watch for symptoms.

Under powers granted by a state of emergency Hogan declared Thursday, the state ordered health insurers to waive all costs for patient testing, which so far has been done by the state lab. Maryland has 1,000 testing kits and expects another shipment next week, when several private lab companies will be cleared to test.

Montgomery County Executive Marc Elrich (D) urged people to avoid sick people on March 6 after three cases of the coronavirus were confirmed in Maryland. (Montgomery County Government)

The search for potential cases involves “a lot of phone calls and left messages and ‘please call me back,’ ” said Assistant Maryland Health Secretary Jinlene Chan. She said health workers in Montgomery County, a suburb of about 1 million people just outside the District, were doing most of the legwork. So far, no one identified as potentially exposed has displayed symptoms that warrant testing, Chan said.

No one from the retirement community has been identified for testing. Hogan said residents and staff should take their temperatures regularly and observe other precautions to quickly identify any possible infections.

“This is exactly what our state has been actively preparing for many weeks,” Hogan said. “I want to again assure Marylanders that all levels of government are working together in response to this threat to public health.”

The individual who tested positive for covid-19 and attended the shiva was a friend of a family member, said the grandson, who asked not to be named to protect his family’s privacy. After learning about the possible exposure, the grandson called a phone number provided by the state and was told he did not need to be tested if he was not showing any symptoms.

As of Friday evening, 44 people in Maryland have been tested for the virus. Results are pending for eight patients, none of whom are connected to the three confirmed infections. Hogan said more results could come this weekend.

“This is changing so quickly,” Chan said. “The guidance we provide right now might change, and that’s based on what’s changing on the ground.”

Sen. Ben Cardin (D-Md.), who toured the National Institutes of Health vaccine research center in Bethesda on Friday afternoon with Sen. Chris Van Hollen (D-Md.), said test kits are being transported to private labs across the country, which should significantly expand the ability to test potential patients.

“It will be reimbursable under Medicare, it will be reimbursable under Medicaid,” Cardin said. “We want to make this an essential health benefit.”

Maryland has received $500,000 from the CDC to help stem the outbreak, Van Hollen’s spokesman said.

Maryland officials said the state contacted the three Montgomery County residents earlier this week, after learning from the CDC that they were on a trip that included exposure to the coronavirus. All are quarantined at home and in good condition.

Hogan said the state is “having trouble getting information from the CDC” about details of the patients’ itinerary, including which countries were visited.

Adam Kurland, 36, said he was “shocked” to learn on social media Friday night of possible exposure at The Village, where his 96-year-old grandmother is a resident. He and his family spent most of the evening trying to get in touch with staff at the facility, without success.

“I’m trying to remain calm, but I’m kind of angry that they haven’t given us more information yet,” Kurland said. “We’re essentially totally in the dark right now.”

Gayles said there is no reason at this point to consider any widespread closures of schools, offices or other institutions in the county. Rather, he said, people who feel sick should stay home, and everyone should take basic precautions like washing their hands, using hand sanitizer and avoiding contact with those who are ill.

Gayles said state investigators have conducted in-depth interviews known as “contact tracing” with all three patients. In general, such interviews are conducted either over the phone, via video link or in person, with the investigators wearing protective gear.

Officials try to map out where a person traveled to before being quarantined, who they came into contact with and what that “quality of interaction” was, Gayles said, taking into account factors like whether they were physically proximate and whether they hugged or shared food.

Each person who had contact with a coronavirus patient is then assigned a risk level, and depending on that assessment, health officials may then decide to do another level of contact tracing.

Montgomery County Executive Marc Elrich (D) urged residents to stay calm: “There is no reason to panic. Life as you know it should continue pretty much as it was.”

Thirty-one Virginia residents have been tested for coronavirus as of Friday, including 21 whose tests came back negative and 10 that are pending. Three of the pending cases are in Northern Virginia. The Virginia state lab has two test kits on hand, which is enough to meet the demand for now, lab spokeswoman Dena Potter said. The state has requested a third kit from the CDC. Each test kit will test 50 to 60 individuals.

Nine D.C. residents have been tested; eight tests came back negative and one is pending.

Meanwhile, the American Israel Public Affairs Committee announced Friday that two people from New York who attended the massive policy conference in Washington early this week had tested positive for the virus. D.C. city officials said the two attendees later confirmed to carry coronavirus did not show symptoms such as fever or cough while they were in the District. Both cases had no identifiable risk to people exposed to them, D.C. officials concluded based on information provided by New York authorities.

“Based on our investigation thus far, in collaboration with the New York State Department of Health (NYSDH), there is no identified risk to conference attendees at this time,” said a statement released by the office of Mayor Muriel E. Bowser (D). “We will work with AIPAC leadership to keep all attendees informed of any new developments.”

The Maryland General Assembly approved Hogan’s request for $50 million from the state’s rainy day fund to deal with the coronavirus. The Metro system launched the second phase of its pandemic response to the coronavirus threat, canceling nonessential business travel and providing hand sanitizer to front-line employees such as Metrobus operators, a Metro spokesman said.

The system activated its pandemic task force, including transit police and emergency management, in January and ordered daily wiping down of heavy traffic areas and steering wheels of Metrobuses and ensuring rail cars go through a hospital-level disinfectant process weekly.

The task force also began monitoring absenteeism to look for patterns that might indicate a rash of illness.

Attorney General Brian E. Frosh (D) warned Maryland residents about scams involving the virus, including websites to sell “bogus health products”; fake emails, texts and social media posts to steal money and personal information; and people posing as the CDC and the WHO.

Frosh recommended residents contact his office’s Consumer Protection Division or report scams to the WHO.

Reps. Gerald E. Connolly (D-Va.), Jennifer Wexton (D-Va.) and John Sarbanes (D-Md.) on Thursday introduced legislation to expand telework across the federal government.

Montgomery County resident Judy Black, 67, stopped by a Bethesda CVS on Friday morning to grab some hand sanitizer — to no avail.

She picked up the store’s last few bottles of antibacterial soap instead, then shared them with others in the checkout line who had come for the same thing.

“It’s a difficult situation,” said Black, a special-education teacher. “It’s not panic, but it’s very difficult to be conscious and cautious and not create panic.”

Black said she is reconsidering her travel plans for the spring, as are many others she has talked with. “A lot of people are wondering whether they should take their kids anywhere for spring break,” she said.

Justin George, Dana Hedgpeth, Fenit Nirappil, Steve Thompson and Ovetta Wiggins contributed to this report.