The Southern State Correctional Facility in Springfield is in lockdown today to help control an outbreak of strep throat.
Acting Superintendent Ellen McWard says about 40 of the 350 inmates are sick.
The lockdown means officials are limiting the number of people who come and go from the prison. In some cases, court appearances by inmates are being postponed.
McWard says the outbreak was first noticed on Sunday. Officials decided yesterday they had to limit exposure and let the outbreak run its course.
McWard says three staff members have also gotten sick.
But none of the cases have been serious enough to require hospitalization.