A patients' group said it is astonished that three inquiries into how medical records came to be strewn on a road failed to find anyone responsible.
The papers were being taken to a waste processing plant
The records belonged to patients from London's Whipps Cross University Hospital and St Bartholomew's Hospital, and London Ambulance Services (LAS).
The papers were found in Northaw, near Potters Bar, Hertfordshire, in January.
Probes by the hospitals trust, LAS and by Bywaters waste management company found their procedures were "robust".
The medical records, which contained details of serious illnesses suffered by patients and outpatient forms, were found by residents in Coopers Lane.
Residents said they had seen documents flying off the back of lorries which they believed were heading for a waste processing plant.
Michael Summers from the Patients Association said: "I find it quite astonishing really that inquiries of this kind have not been able to reveal how these records came to be missing and found in the street.
"It's a whole series of events of this kind that cause patients so much distress.
"What they say to their doctors they hope to remain confidential and they don't expect it to be left lying around or lost without explanation."
A statement from The Whipps Cross University Hospital NHS Trust, based in Leytonstone, east London, said: "The trust is confident that its internal procedures for its disposal of confidential waste on site are robust.
"The trust has received written assurance from both Bywaters and its sub-contractors that its confidential material will only be disposed of at the site in Kent the trust has visited and quality assured."
A statement from Bywaters Waste Management Company, which processes the waste for both the hospitals and LAS, said: "The treatment of our customers' confidential waste is paramount and we have full confidence in our sub-contractors' processes and procedures."
LAS, which also conducted a separate inquiry, said it found "no fault in our internal procedures".
A statement said: "As a result of what happened however we have worked with our third-party contractor to ensure the arrangements for the disposal of confidential waste are as robust as possible.
"We are now shredding all confidential material on site."