An autistic woman in her 50s discovered to be infected with HIV after being raped by a night shift worker at some point between 2006 and 2016 at a facility run by a private company in Brent.
The victim renamed as 'Cassie' in the report to protect her identity, was found to have HIV after she collapsed in 2016 and was taken to Guy's Hospital.
She had been in care since childhood and began suffering from rashes, bruising, teeth problems and had lost her appetite from around 2007, the report said.
Police were called when it was ruled by doctors that the disease was sexually transmitted and she lacked the mental capability to consent to sex.
Professor Michael Preston-Shoot, chairman of the Brent Safeguarding Adults Board, said: "This is a distressing case of a woman who should have been safe but has acquired a serious infection probably as a result of sexual abuse.
“The board wishes to express its deep and sincere regret to Adult B and her family.”
A Metropolitan Police spokesman confirmed the investigation was closed in 2017 as there were no new lines of inquiry.
He added: "Due to the 10-year period the offense was alleged to have occurred between, no clear suspects could be identified and there were no forensic opportunities available.
The home has now been closed and all residents are at new facilities.
Brent Council said the Labour-controlled authority no longer places residents with the private company.