"In 2015, correctional administrators reported 24,661 allegations of sexual victimization in prisons, jails, and other adult correctional facilities. More than half (58%) involved sexual victimization by staff toward inmates, and the remainder (42%) involved sexual victimization by inmates towards other inmates. About 8% (1,473) of the allegations were substantiated based on completed investigations. The number of allegations rose sharply after the National Standards to Prevent, Detect, and Respond to Prison Rape were issued by the Department of Justice in 2012. The standards require correctional facilities to educate staff and inmates on sexual victimization, refer all allegations for investigation, track the information collected in the Survey of Sexual Victimization (SSV), and provide the information on request."
Bureau of Justice Statistics: https://www.bjs.gov/