And almost two-fifths of trusts openly discuss incidents with patients and families in half or less than half of the incidents, the study found.
Barriers to openness with patients or their families include fear of blame or litigation or being accused of malpractice and feelings of guilt, according to the research published online in BMJ Quality and Safety.
Some trusts have failed to recognise the importance of openness with patients about mistakes, the authors said.
Trusts should examine the way they manage openness with patients and their families and make sure the appropriate support mechanisms are in place, they added.
The researchers, from Imperial College London, questioned 209 patient safety managers at trusts in England.
They found that almost all were familiar with the National Patient Safety Agency’s Being Open guidance, released in 2005 and again in 2009.
Hospitals were told to be open and truthful about causing harm instead of taking a defensive and legalistic approach.
But 9 per cent of trusts said they did not have a “board-approved” policy on open disclosure.
The researchers also found that disclosure policies were less likely to be implemented when the incident was resolved and the patient made a full recovery.
In two-thirds of trusts the first open disclosure meeting with patients and their families did not happen until three to six months after the trust’s own investigation into the incident, they found.
“A particularly worrying finding is that a high proportion of patient safety managers reported that the first open meeting with patients and families takes place three to six months after the investigation, which itself may have lasted some months,” the authors wrote.
“This implies that many patients and families are waiting up to a year before any clear explanation of serious incidents is given, which is extremely stressful in many cases.
“Patients are in favour of prompt provision of information about things that go wrong in their care and this delay in itself is likely to exacerbate the distress already caused, erode trust and may also increase the likelihood of further complaints and litigation.
“The survey also suggests that there is limited representation of clinical staff in comparison to managers at open disclosure meetings, despite evidence suggesting that patients attach great importance to clinical staff who are involved in patient safety incidents being also involved in the communication of the incidents to the patients.”
The authors concluded: “Our findings suggest that there is high awareness among patient safety managers of the importance of being more open with patients, but that progress is slow and that some trusts have simply failed to recognise the importance of this issue.
“Our findings highlight the need for NHS trusts to look closely into the ways in which they manage the aftermath of patient safety incidents and to ensure that sensitive support mechanisms are in place for patients, families and staff.”