A nurse who was looking after an incapacitated woman at a long-term health care facility has been charged with raping her, weeks after the patient stunned her caregivers and family by giving birth to a boy, Phoenix police said Wednesday.

Investigators arrested 36-year-old Nathan Sutherland, a licensed practical nurse, on suspicion of one count of sexual assault and one count of vulnerable adult abuse, Phoenix Police Chief Jeri Williams said.

"We owed this arrest to the victim. We owed this arrest to the newest member of our community — that innocent baby," Williams said.

Williams said Sutherland worked at the Hacienda HealthCare facility where the woman lived and he had been providing care to her.

Nathan Sutherland, charged with raping an incapacitated woman at a long-term health-care facility, is shown in a booking photo provided Wednesday by the Maricopa Sheriff's Office. (Reuters)

The surprise birth on Dec. 29 triggered reviews by state agencies and highlighted safety concerns for patients who are severely disabled or incapacitated. It also prompted authorities to test the DNA of all the men who worked at the Hacienda HealthCare facility.

Sutherland submitted his DNA sample under court order Tuesday, and the results came back a few hours later, showing he was a match to the baby. He declined to speak with police and invoked his Fifth Amendment rights, Phoenix police spokesperson Sgt. Tommy Thompson said.

Sutherland, wearing a T-shirt, black athletic pants and jacket, appeared in court Wednesday. A Maricopa County Superior Court commissioner ordered him released on a cash-only $500,000 US bond. He also must wear an electronic monitoring device.

Defence attorney David Gregan had asked for a lower bond, citing Sutherland's lack of a criminal record. He described Sutherland as a family man with young children who has lived in Arizona since 1993.

"There's no direct evidence that Mr. Sutherland has committed these acts," Gregan said. "I know at this point there's DNA. But he will have a right to his own DNA expert."

'Troubled beyond words'

Hacienda HealthCare said in a statement Wednesday that Sutherland was terminated after police announced his arrest.

Hacienda said its officials are "troubled beyond words" that someone who passed an extensive background check could harm a patient and that officials will continue co-operating with police.

"Once again, we offer an apology and send our deepest sympathies to the client and her family, to the community and to our agency partners at every level," Hacienda said in a statement.

The case has prompted the departure or discipline of key figures at Hacienda HealthCare, including the CEO. The provider on Sunday announced that a doctor who had cared for the woman resigned and another had been suspended.

The 29-year-old woman has been incapacitated since she was three.

Earlier reports had indicated the woman was in a coma. Her family, in a statement Tuesday through their lawyer, said that was not the case.

"She has significant intellectual disabilities as a result of seizures very early in her childhood," the statement said.

Hacienda HealthCare in Phoenix is shown in a photo earlier this month. Police say DNA testing led to a court order for the arrest of the suspect in the case. (Ross D. Franklin/Associated Press)

"She does not speak but has some ability to move her limbs, head and neck. Their daughter responds to sound and is able to make facial gestures. The important thing is that she is a beloved daughter, albeit with significant intellectual disabilities."

Employees said they had no idea she was pregnant. Her last known physical was in April 2018, according to court records.

The woman's family has said they will take care of the child.