The chances are very very very remote, almost negligible... We don't have exact statistics for the risk of acquiring HIV through such route. There is a remote chance of getting it if the trimmer had been used in a positive patient with high viral load (ie not on treatment) in the past 15 min and he had sustained an injury with that and his blood is still on the trimmer tip. The chances are only 0.03 % for health care workers who accidentally get pricked from needles that were used in HIV positive patients. ( proven by blood tests)