Robert Edward MacDonnell, 44, of the 400 block of Leeds Ridge Court, Purcellville, has been charged with object sexual penetration. He is being held without bond.
Prince William County Police detectives were notified of the incident Dec. 19, 2013, according to police spokesperson Officer Jonathan Perok. The incident allegedly happened in September 2012 at the Dumfries Health Center, 3700 Fettler Park Drive, in Dumfries.
The victim was 21 years old at the time of the incident and a patient of MacDonnell's, according to police.
"The investigation revealed that the victim was sexually assaulted by the accused on at least one occasion while in his care during that time," Perok said in a statement.