42 C.F.R. § 440.80
Private duty nursing services means nursing services for beneficiaries who require more individual and continuous care than is available from a visiting nurse or routinely provided by the nursing staff of the hospital or skilled nursing facility. These services are provided—
(c) To a beneficiary in one or more of the following locations at the option of the State—
[52 FR 47934, Dec. 17, 1987]