197 reports of sexual misconduct were made against state prison staff [from 2005 to 2007]. Of the complaints logged between 2005 and 2007, 62 cases were substantiated and resulted in firings, Colorado Department of Corrections spokeswoman Katherine Sanguinetti said Thursday. The DOC's inspector general turned over the complaints to local prosecutors.
From here. Related Colorado Department of Correction Report here.
This is in a prison system of 23,000 inmates and presumably significantly fewer guards.
Some cases, such as a case decided this week involving a guard convicted of sexual assault on a female inmate against whom a $1.3 million judgment was awarded this week (on top of a $250,000 judgment against the Colorado Department of Corrections) involve deliberate indifference by other prison staff and lead to underreporting and failure to substantiate incidents that do happen.
A large share of prison rapes are by other inmates, and the most 2007 government study estimated that 4.7% of inmates have been sexually assaulted by either staff or other inmates in the last twelve months.
Released inmates account for 13% to 19% of all HIV cases and 17% of all AIDS cases in the general population.