BATH — Bath Iron Works, one of the state’s largest employers, reported swelling COVID-19 cases last week in the main shipyard in Bath and a structural fabrication facility known as the Harding Plant in Brunswick.

BIW, a subsidiary of aerospace and defense company General Dynamics, has seen 37 workers test positive since March. Of those, 17 are considered “active cases,” meaning the employees haven’t yet returned to work, said BIW spokesman David Hench.

Last week, the company confirmed seven employees tested positive for COVID-19 between Monday and Wednesday, all but one of whom worked in the main shipyard. Those seven workers were last at work between Nov. 18 and Nov. 20, according to the company’s website.

The week before, the shipyard announced a dozen other employees from the main shipyard and Harding Plant tested positive for COVID-19. Those employees were last at work between Nov. 11 and Nov. 18. As a result, the Maine Center for Disease Control and Prevention last week launched an investigation into the outbreaks.

The company started offering free tests to employees at the facilities where cases were growing on Monday, but withdrew the offer two days later, citing “the increasing statewide demand for COVID-19 testing.”

Employees are being directed to local testing sites, according to a statement from the company posted Wednesday. Neither Hench nor Maine CDC spokesman Robert Long could say how many shipbuilders have been tested or will need to be tested due to close contact with a sick coworker.

“Maine CDC worked with BIW and partners to make testing available to shipyard employees,” said Long. “It is voluntary, so the number of tests will depend on how many BIW employees take advantage of the various testing options available to them.”

Hench said the shipyard doesn’t yet know how many employees will be asked to self-quarantine as contract tracing is ongoing.

Despite the mounting number of cases in the shipyard, Hench said the company will not close any facilities because it was “designated infrastructure essential to our national security by the Department of Homeland Security in March.”

“As such, like other shipyards and essential businesses in the country, we must maintain operations, in accordance with CDC guidelines, in support of our Navy Customer while ensuring the health and safety of our employees, their families, and our surrounding communities,” he said.

BIW’s surge in COVID-19 cases mirrors statewide trends, but local case numbers remain low. The shipyard employs 6,800 people from every county in the state.

In Bath, with a population of 11,031, 40 people had tested positive for COVID-19 as of Sunday, according to the Maine CDC. Neighboring Brunswick, with nearly double the population, has seen 91 cases since March.

Mid Coast Hospital in Brunswick is treating three patients for COVID-19, according to spokeswoman Judith Kelsh. The hospital has treated 31 patients for COVID-19 since March. This month, Mid Coast Hospital has tested 3,304 individuals for COVID-19, 68 of which yielded positive results as of Sunday. Since March, 172 people have tested positive at Mid Coast Hospital.

Sagadahoc County has among the lowest number of positive cases, with just 149 as of Sunday, according to the Maine CDC. Long credited the county’s low case rate to its low population compared to neighboring Cumberland and Androscoggin counties, which hold the most and third most cases in the state, respectively. Cumberland and Androscoggin counties have a population of 295,003 and 108,277, respectively, according to the U.S. Census Bureau. Sagadahoc County has just 35,856 residents.

“That said, we urge the residents of Sagadahoc County not to develop a false sense of security,” said Long. “Maine CDC continues to recommend that people everywhere in Maine live their lives with the understanding that the virus is in their neighborhood.”

Long continues to urge Mainers to wear face masks in public, maintain a 6-foot distance from others, and avoid nonessential gatherings because “these are the best tools that Maine people have to slow the spread of the virus.”

Maine has experienced a surge in statewide COVID-19 cases this month. State health officials reported over 200 new daily cases 11 times in the last three weeks. The 7-day average of new cases sits at 165 cases, compared to just 40 cases one month ago.

According to the Maine CDC, 11,508 Mainers have tested positive for COVID-19 since the pandemic reached Maine in March. Of those, 8,952 have recovered, but 191 have died as of Sunday.