Testing for COVID-19 last week of all 1,273 inmates in Stillwater prison revealed an outbreak of 90 positive cases as the facility is kept on lockdown to address the deadly disease, state officials reported over the weekend.

The lockdown, which began Saturday, "will allow us to prevent any further spread," according to an announcement Sunday afternoon from the Minnesota Department of Corrections (DOC).

Stillwater's inmates had remained free of the novel corona­virus until late September, said DOC spokeswoman Sarah Fitzgerald.

While most among the 7% of inmates who tested positive last week are showing either mild or no symptoms, their conditions are being monitored for any worsening, the DOC said.

One inmate who tested positive last week, a 70-year-old, has been moved out of the men's facility for medical attention, the DOC said.

All but two of the positive cases were in two living units: Cell Hall D and Atlantis. The others were in B-West and A-East.

Last week's detection of the outbreak brings the facility's overall COVID-19 case tally to 115.

Among Cell Hall D's 184 inmates, 87 (47%) have now contracted COVID-19, while all 28 residents have the disease in Atlantis because it has been converted from handling substance-abuse cases into a corona­virus quarantine unit because it is "small and isolated away from the rest of the facility," Fitzgerald said.

Inmates testing positive in Cell Hall D and Atlantis will stay in place in their units. On Monday, the men resumed having access to phones and showers within their units.

Visits to the prison are halted during the lockdown's duration. Many other DOC facilities with positive cases among inmates or staff are also barring visits in response to the pandemic.

Prisoners with COVID-19 may leave their cells only with others who also have tested positive, and the same goes for those who have tested negative, the DOC said.

"The units will be entirely disinfected between movement of positive and negative groups," the agency's announcement read.

Stillwater Warden Guy Bosch said in a statement that "we have long since recognized the challenge of keeping COVID-19 entirely out of this facility, and we planned for the likelihood that we would have cases here. Our 'Stay with Unit' plan has helped contain the spread of this outbreak within two living units."

Corrections officers and other staff, however, are still able to move to a degree from one unit to another, DOC spokeswoman Fitzgerald said.

"As much as we are able to, we keep staff from crossing into different units," she said, "but in a security environment, it isn't always possible to prevent. Staff are always wearing the appropriate protection."

Since the pandemic began, 754 state prisoners have tested positive for the respiratory disease, according to the latest tally released Monday afternoon. Two of them, both at the Faribault prison, have died.

Among staff across the Department of Corrections system, the agency said it has had 176 confirmed positive COVID-19 cases and another 10 classified as presumed positive.

Stillwater's recent outbreak falls far short of the spread of COVID-19 at the Faribault prison, where more than 200 inmates tested positive in June.