Of the 28 total cases, 27 are presumptive cases that were tested by the state lab and need confirmation by the US Centers for Disease Control; one has been confirmed by the CDC. Nine of those cases involve Boston residents, according to the Boston Public Health Commission.

The new cases bring the state’s total to 28, more than double the number reported the day before.

A company meeting of biotech giant Biogen in Boston last month was linked to nearly two dozen cases of coronavirus in Massachusetts Sunday, according to state public health authorities, who reported 15 new cases.

All 15 of the new cases reported Sunday were tied to Biogen’s late February meeting of top managers at the Boston Marriott Long Wharf hotel, according to a statement from the Massacusetts Department of Public Health.


On Sunday, the company said an executive who attended that meeting, and a later Boston conference, has tested positive for the virus.

In a statement Sunday, Biogen said its priority is the safety of its community: “We have been working closely with the public health authorities to assist in their effort to assure that appropriate parties are tested for Covid-19 and proper follow-up precautions are initiated.”

That meeting drew about 175 participants, who have been advised to self-quarantine and monitor themselves for symptoms for Covid-19, the illness caused by the coronavirus, said Ann Scales, a spokeswoman for the Department of Public Health.

Twenty-three of the state’s cases are linked to the Biogen meeting, the state public health department said.

The risk of Covid-19 to the general public in Massachusetts remains low at this time, state health officials said.

The Boston Public Health Commission said that the five Boston residents whose cases were reported Sunday include a woman in her 30s, a woman in her 60s, a man in his 40s, a man in his 50s, and a man in his 60s, the agency said in a statement.


All five attended the Biogen meeting and did not require hospitalization. They are self-isolating at home, the health commission said.

The state public health department reported Sunday that the remaining new cases include five people in Middlesex County and four in Norfolk County, who range in age from their 40s to their 60s.

The remaining case reported Sunday involved a female, but her age and county of residence were unknown, the state health department said Sunday.

On Saturday, Massachusetts health officials disclosed five new cases of Covid-19, including a Berkshire county man in his 60s who was hospitalized at Berkshire Medical Center. He remained in stable condition Sunday afternoon, a hospital spokesman said.

As of Sunday evening, there were 537Covid-19 cases in the United States, along with 21 deaths: 18 in Washington state, two in Florida, and one in California, according to a database of cases maintained by Johns Hopkins University.

The scope of the infections linked to Biogen’s meeting appeared to grow Sunday.

Biogen reported Sunday that one of its executives who attended a conference organized early this month by the investment bank Cowen & Co., which drew representatives from more than 300 companies, has also tested positive for Covid-19.

Following Biogen’s company meeting in February, four executives from that company participated in Cowen’s conference, which was held at Boston Marriott Copley Place on March 2. Two of them fell ill after the Cowen event, and one later tested positive for the virus, the company said Sunday.


“This person is recovering well and in isolation,” Biogen said in a statement. “This person will be supplying their close contacts to the public health authorities, who will follow up.”

In Indiana on Sunday, health officials said two cases in that state involved people who had attended the Biogen meeting in Boston. Neither is hospitalized, according to a statement from the Indiana State Department of Health.

Locally, in Wellesley and Norwood, one resident in each of those communities who attended the Biogen meeting has tested positive for presumptive cases of the virus.

The Wellesley case led to the early closure of two schools Friday, while in Norwood, 30 people — including 11 town officials — have been ordered to self-quarantine after attending a party with a person who later became sick.

In Arlington, a parent who attended the Biogen meeting has tested positive for the coronavirus, and their child, who is a student in the town’s public schools, is also showing symptoms, officials said in a statement Sunday night. The child has been tested, and officials are awaiting results, prompting the closure of the Stratton Elementary School on Monday.

“Without test results in hand, and with a parent who has tested positive for COVID-19, the leadership team in Arlington unanimously feels that it is best to close the Stratton on Monday and re-evaluate during the day,” said Arlington’s schools superintendent, Kathleen Bodie, in the statement.


In Newton, school Superintendent David Fleishman said in an e-mail to the community Sunday night that a parent of a child at the Horace Mann Elementary School received a presumed positive test result for the virus. The student, who is not exhibiting symptoms, will not return to school until the child completes the state’s quarantine protocol, Fleishman said.

Officials in those communities said schools were disinfected over the weekend and were expected to be open for classes Monday.

In Concord, a patient at Emerson Hospital recently tested positive for the virus, according to a statement from Emerson’s chief medical officer, Barrett Kitch.

The patient, who had traveled abroad, had mild symptoms and called the hospital in advance so officials could take precautions before being tested, the statement said. The case still needs to be confirmed by the CDC.

Kitch said the patient is at home under quarantine, and he emphasized there was no current risk of exposure for anyone at the hospital.

“The team followed protocols and made every precautionary measure to protect patients, visitors, and staff,” Kitch said. "The Emerson team who interacted with the patient will not require quarantine.”

Elsewhere in New England, several cases of the virus were reported over the weekend by health officials.

On Saturday, New Hampshire health officials said they had two presumptive positive cases of Covid-19, raising the state’s total to four cases. The new cases involved a man who became ill after coming in contact with the virus at a church; the other case involved a man who had traveled to Italy.


In Vermont, officials said Sunday the state’s one patient who has tested positive for the virus was hospitalized in an airborne-infection isolation room.

And on Saturday, Austrian media reported that a woman who was in Boston for a conference has since tested positive for the virus, along with members of her family.

It was not clear whether that woman’s case is connected to the Biogen meeting.

Concerns about the coronavirus were on the minds of some visitors at the Museum of Science who filled most of an auditorium late Sunday afternoon for a panel discussion about the outbreak.

“We’re older,” said Susan Markowitz, 71, of Cambridge, who came with a pair of friends. “We’re relatively healthy, but we just want to make sure we’re doing everything properly.”

Ophelia Deng, 20, a Boston University student from Xiamen, China, said she worried she was watching the same outbreak twice. The first time was in China, she said, and now in the United States.

“People should start to take more precautions,” Deng said.

The museum’s president, Tim Ritchie, said the discussion was the first part of an institutional effort to educate citizens on the dangers of coronavirus that will include physical exhibits in the near future.

“We deeply believe people should take an evidence-based approach to this, and there’s a lot of misinformation out there,” Ritchie said. “So we want people to have the categories they need for making wise decisions as [the outbreak] evolves.”

Globe correspondents Max Jungreis and Abigail Feldman contributed to this report.

John Hilliard can be reached at john.hilliard@globe.com.