MUSKEGON, Mich. (WOOD) — An outbreak of COVID-19 at the Muskegon Correctional Facility has ballooned to 155 cases, state officials say.

The Michigan Department of Corrections told News 8 earlier this week there were 19 cases identified at the prison — 17 among inmates and two among staff members — and it was expecting more. On Wednesday, MDOC spokesman Chris Gautz told News 8 the figure had climbed to a total of 155 after “mass testing.”

Gautz said two full housing units were tested Friday after the initial cases were identified. Of 447 inmates tested Friday, 136 were positive, 309 were negative and two were inconclusive.

The two inmates whose results were inconclusive are being retested.

The rest of the prison’s population — more than 760 inmates — were tested Tuesday. Those results should be back by the end of the week, Gautz said.

All staff members can get tested for free Wednesday and Thursday.

Following the protocol MDOC set up earlier in the outbreak, those who have tested positive are being moved out of the Muskegon prison to a facility that’s only housing COVID-19 patients. The remaining prisoners now have restricted movement throughout the prison and are interacting only with the same cohort of inmates to limit the spread of the virus.

All inmates will be tested again next week. Prisoners may also undergo antibody testing to determine if they previously had the virus.

Gautz said earlier this week that the virus was likely introduced to the prison population via staff members going in and out.

“We are certainly going through that when we look at the employee positives,” he said. “We look at where they’ve been, who they are in contact with. So we have a pretty good idea, but we want to do more investigation so that we can really be certain.”