Among the more severe transgressions documented in the report were the use of restraints to manage difficult behavior, sexual abuse of female patients, sleeping on floors, restrictions on communication and little access to "meaningful daily activities."
The assessment determines where current standards conflicted with guidelines laid out in the United Nations Convention on the Rights of Persons with Disabilities.
"I think it's very clear that this inequality of treatment that the most vulnerable people in society are getting is unacceptable. They're being excluded from their communities and society; they're being institutionalized, which deskills them; and often, this kind of care is more expensive as well," said Dr. Sri Kalidindi, a spokeswoman for the Royal College of Psychiatrists in the UK who wasn't involved in the study.
Long-stay mental health institutions are still the central providers of mental health care for people with psychosocial and intellectual disabilities in the WHO European region. However, little is actually known about the services and quality of care they offer some of Europe's most "neglected and stigmatized" people, according to the report.
"We have now developed new guidance and materials, which we can now use to work with countries to improve those specific areas of concern or the shortcomings shown in this work," said Dr. Daniel Chisholm, program manager for mental health at the WHO regional office in Europe and one of the authors of the report.
The results, which were released Wednesday, were part of a large study carried out in 2017 in 75 institutions across 24 European countries and Kosovo. Institutions were graded using 25 standards and 116 criteria.
Results varied by country and institution. But the overarching finding was the large-scale violation of fundamental rights of institutions' patients, including "their legal capacity, autonomy, dignity, liberty and security of person, physical and mental integrity and freedom from torture and ill treatment and from exploitation, violence and abuse."
Fewer than a third of the 2,450 total ratings were at a satisfactory level, meaning those countries that agreed to the UN convention are at risk of violating the treaty.
The Convention on the Rights of Persons with Disabilities was ratified in 2006 as a way of formally implementing a rights-based model of disability, according to the study.
The deinstitutionalization of people with cognitive, intellectual and psychosocial disabilities is a central goal for WHO, and experts hope the study will motivate this change.
"This study is the first one that really shows an organized picture by using the assessment instrument of the WHO. I hope that this will help us to create a strong front to move forward toward deinstitutionalization," said Melita Murko, technical officer for the WHO Mental Health Programme and co-author of the study.
Furthermore, experts believe the collaboration between countries and WHO during the assessment was a step toward improving current conditions.
"Getting countries to collaborate and engage in this process is in itself something of an accomplishment, irrespective of what the findings of the report present," Chisholm said.
"For the countries and organizations that have taken part in the study, it's clear that they've already started to reflect on where they currently are and where they could change," Kalidindi said. "Now, it's key that everybody in the system, both the government, patients and their families, should be working together to create what a good system looks like according to that country."
With these results, WHO plans to work with European countries to deinstitutionalize and expand community-based systems of mental health care, where specialized services, outreach programs and social and welfare services are offered.
"They are not just victims or someone that has this lifelong diagnosis and nothing can be done for them. Of course, there is something that can be done," Chisholm said.