The chief executive of the corporation that runs a private nursing home in Arizona where a woman in a vegetative state was sexually assaulted and later gave birth to a child resigned on Monday, the company said in a statement.

The company, Hacienda HealthCare, said the resignation of the executive, Bill Timmons, was unanimously accepted by its board of directors. David Leibowitz, a company spokesperson, said Mr Timmons had been chief executive for 28 years. Efforts to reach Mr Timmons on Monday night were unsuccessful.

Gary Orman, executive vice president of the company’s board, said it would “accept nothing less than a full accounting of this absolutely horrifying situation, an unprecedented case that has devastated everyone involved, from the victim and her family to Hacienda staff at every level of our organisation.”

Hacienda HealthCare has been under intense scrutiny since the Phoenix Police Department said last week that it had opened an investigation into the circumstances surrounding the conception of the child, who was born last month. The woman has not been publicly identified.

A spokesperson at the Arizona Department of Health Services said it was also aware of the allegations and would conduct an inspection of the Hacienda Nursing Facility. Records posted to the Medicare website indicate the care centre received a “below average” rating from health inspectors in 2017. The Centres for Medicare & Medicaid Services rated its quality of resident care as “much below average.”

“I want to assure our patients, their loved ones, our community partners, the agencies we do business with, Governor Ducey and the residents of Arizona, we will continue to cooperate with Phoenix police and the investigating agencies at all levels in every way possible,” Mr Orman said in the statement. “And we will do everything in our power to ensure the safety of every single one of our patients and our employees.”

The nursing home, which is about 7 miles south of downtown Phoenix, specialises in the care of people with intellectual disabilities and has at least 74 patient beds, according to federal records. State records indicate some patients have lived there for decades.

This is not the first time investigators have expressed concern about the facility.

In 2013, the Arizona Department of Health Services found a male employee mistreated some patients by making sexually explicit remarks about them. A state report issued at the time did not allege physical abuse at the centre, and its operators said the employee in question had been fired. It said employees would be given new training on how to report the suspected abuse of patients.

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In 2017, state investigators cited the facility for providing inadequate privacy to patients while they were naked or being showered. A report issued at the time reminded the centre it had an obligation to its residents.

“Federal and state laws guarantee certain basic rights to all residents of this facility and they include the right to a dignified existence and to be treated with dignity,” it said.