KPHO-TV, Phoenix, reported Tuesday the outbreak started with five prisoners getting sick Saturday in the Special Management Unit 1 at the Arizona State Prison Complex Eyman in Florence. Two more fell ill Sunday.
All seven inmates were in intensive care, the TV station said.
Pinal County Public Health officials and staff from the state Departments of Corrections and Health Services are investigating suspicions that the inmates may have contracted the botulism poisoning from homemade alcohol made from fermented fruit.
Samples of the alcohol were sent for testing and officials were awaiting the lab results, KPHO-TV said.
Botulism causes muscle weakness and difficulty speaking, chewing or swallowing. Left untreated, it can lead to paralysis.