ATTLEBORO, MA — A week after a firefighter within the Attleboro Fire Department tested positive for the coronavirus, eight more firefighters and two dispatchers have also been diagnosed with confirmed cases, town officials have announced.

Attleboro Mayor Paul Heroux and Fire Chief Scott Lachance confirmed the positive cases in a news release this week. The 11 confirmed cases were as of Tuesday, officials said, and were all tied to one shift of the department. Most of those who tested positive were asymptomatic or have mild symptoms but one firefighter became seriously ill and is currently hospitalized in serious condition at Rhode Island Hospital, officials said.

Heroux told Patch on Thursday that there have been no further confirmed cases since Monday and that as of Thursday, 57 people within the department have tested negative, including nine negative tests on Thursday.

Since the outbreak began, aggressive testing and re-testing of firefighters and other employees of the department is ongoing. The entire Attleboro Fire Department, including all living quarters, stations, communications centers and equipment have been professionally disinfected by a contract vendor. Heroux said that new HEPA air filtration systems have been installed at four fire stations and said that similar systems will be installed at city offices where two or more people work.

Despite the outbreak, there has been no disruption of service and the department, Heroux and Lachance said, has the ability to fully staff shifts so that emergency calls can be handled with normal levels of staffing. The nine firefighters that have tested positive represent about 10 percent of the department.

The outbreak is the first positive coronavirus case within the department since March, Heroux said. Over the past months, firefighters have transported 400 coronavirus patients and have avoided becoming infected. Before last week, firefighters and other employees were tested if they came into contact with someone who had tested positive. Since then, the department has upped the amount of testing amid the outbreak out of an abundance of caution.

Heroux said he is not surprised an outbreak did not happen before now, which he said, serves as a testament to the attention the department has been paying to the coronavirus. But with students returning to school and people being indoors now perhaps more than before, Heroux believes it makes more sense this happened now rather than in previous months.

“I’m not surprised this eventually happened because firefighters are living in close proximity to each other, they eat together, they’re watch TV together, they’re sleeping in the same quarters,” the mayor said Thursday. “They’re basically breathing the same air.”

The outbreak comes at a time when Attleboro was added to Massachusetts’ red zone, designating it as a place where at least 60 confirmed cases have been discovered over the past two weeks. Still, Heroux, who said an outbreak of the virus within the department was “kind of inevitable”, he believes the department will get through its current situation.

“Because of the actions of the fire chief and the cooperation of the firefighters, I have every confidence that this situation is under control and that the services that the fire department provides to the community will continue as needed,” Heroux said in the news release.

Heroux, who is in daily communication with Lachance, said officials have not determined what caused the outbreak in the department. Despite efforts to minimize the spread of the coronavirus within the department, Heroux said that it is clear that the virus was being spread while the firefighters were at work.

“We are working with the city’s health department, conducting contact tracing and continuing to take all the necessary precautions to keep our members and the public safe,” Lachance said in the news release.

This article originally appeared on the Attleboro Patch