BATH — Bath Iron Works, one of the state’s largest employers, continues to report increasing COVID-19 cases, mostly among employees who work inside the ships.

BIW, a subsidiary of General Dynamics, has reported new cases nearly every day for the past five weeks. As of Wednesday, 57 workers have tested positive so far this month, according to the company’s website.

Since Dec. 14, 20 workers have tested positive for COVID-19, according to the company’s website. Those workers were last at work between Dec. 1 and Dec. 19.

The increasing number of cases across multiple company facilities caused the Maine Center for Disease Control and Prevention to launch an outbreak investigation at the company.

BIW spokesman David Hench said BIW will “continue to follow CDC recommendations to stop the spread.”

“As COVID-19 cases surge in Maine and across the country, we strongly urge all of our employees to remain vigilant and consistently adhere to COVID-19 safe practices as recommended by the Centers for Disease Control, including wearing a face covering and maintaining social distancing,” Hench said Wednesday. “As always – and especially during the pandemic – we encourage all employees to be mindful of their own safety and that of their coworkers, their families and the greater community.”

The shipyard reported 105 workers have tested positive since the COVID-19 pandemic reached Maine in March, 17 of which are considered active, according to Hench.

Of the 105 workers who have tested positive, 46 of them work within the Land Level Transfer Facility and Piers, where ships are assembled and finished at the main shipyard on Washington Street in Bath. It’s also where the majority of the company’s 6,650 employees work.

Although ships are assembled outside in that stage of the building progress, many shipbuilders work within the ships themselves. This means multiple employees could work in tight, enclosed spaces for extended periods of time, which could increase their risk.

In a 1989 study conducted by the CDC after a tuberculosis outbreak at the shipyard infected over 570 workers, the CDC noted “Workers on the ships work in small, enclosed areas. … Conditions on the ships are frequently crowded; physical contact with people in some areas (passageways and cubbyholes) is almost impossible to avoid.”

Both the Center for Disease Control and Prevention and the World Health Organization have maintained that wearing a face mask and staying at least six feet away from others are the best ways to mitigate the spread of COVID-19.

The company made masks mandatory for all workers and increased daily sanitization efforts, but it has held firm that it will not close, as ordered by the Navy.

“When COVID-19 first hit, we were reminded of the pivotal role Bath Iron Works plays when the Department of Homeland Security designated us as critical infrastructure,” BIW President Dirk Lesko said Tuesday in a year-end address to employees.

While BIW workers continue to test positive, the company has avoided widespread outbreaks, mirroring local cases, as statewide cases skyrocket.

Mid Coast Hospital in Brunswick is treating nine patients for COVID-19, according to spokeswoman Judy Kelsh. The hospital has treated 60 patients for COVID-19 since March. This month, Mid Coast Hospital has tested 3,268 individuals for COVID-19, 122 of which yielded positive results as of Wednesday. Since March, 328 people have tested positive at Mid Coast Hospital.

State health officials reported 748 new cases of COVID-19 on Wednesday, a new single-day case record, as well as eight additional deaths among infected people, the Portland Press Herald reported.

Maine’s cumulative cases rose to 20,491 on Wednesday and 311 people have died with COVID-19 since the pandemic began in Maine.