UPDATE, March 9: The number of cases rose again on Monday. Details here.

The number of confirmed or presumptive positive cases of the novel coronavirus in Massachusetts has jumped to 28, up from 13 on Saturday, according to state health officials.

Twenty-seven of the state's cases are presumed to be positive, state officials say. One case has been confirmed by the U.S. Centers for Disease Control and Prevention.

Fifteen new presumptive positive cases of the virus were announced by the Massachusetts Department of Public Health on Sunday, including five in Boston.

State health officials say all 15 cases — eight men and seven women — had a direct connection to a conference held by the biotech company Biogen from Feb. 24 to 27 at the Marriott Long Wharf in Boston's Seaport District.

The new cases include five people from Suffolk County ranging in age from their 30s to 60s; five people from Middlesex County ranging in age from their 40s to 60s; four people from Norfolk County ranging in age from their 40s to 60s; and a woman whose age and county are not known at this time.

The Boston Public Health Commission announced the five new Suffolk County cases 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. None of them have required hospitalization and all are self-isolating at home.

State health officials said all 15 people announced as presumptive positive cases on Sunday were in quarantine at their homes.

Of the state's 27 presumptive positive cases of COVID-19, officials say 23 of them are associated with the Biogen employee conference held in late February.

On Saturday, the DPH announced five new presumptive positive cases, three of which had a direct connection to Biogen’s employee conference, one with recent international travel including northern Italy and a fifth case for whom there is no current known linkage to the Biogen conference or foreign travel.

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

City health officials say there is currently no evidence of community transmission in Boston and that the risk remains low at this time.

The state's first and only confirmed case of the coronavirus was announced on Feb. 1 in a university student who had recently traveled back to Boston from Wuhan, China. The UMass Boston student, who is in his 20s and lives in Boston, returned from China on Jan. 28 and sought medical attention the following day for a runny nose. His case was confirmed Jan. 31 and he was quarantined in his home, according to health officials. The man's few close contacts were identified and monitored for any signs of symptoms.

As of Wednesday, March 4, officials said 719 people have been subject to self-quarantine in Massachusetts because of COVID-19. Of those, 470 people have completed monitoring and are no longer quarantined, while 249 are currently quarantined.