Skilled nursing facilities need to improve staff training on detecting and managing sexual assault cases in order to protect their most vulnerable residents, a new academic review asserts.

The research, published online Wednesday in The Gerontologist, was gathered by a team at Australia’s Monash University from more than a dozen previously published studies on sexual assaults within nursing homes and other long-term care facilities. The review’s authors sought to shed light on the characteristics of assault incidents, including the relationship between the victims and the perpetrators, legal outcomes and preventative measures taken by facilities.

Victims of sexual assaults within nursing homes tend to be white females suffering from some sort of mental or physical impairment, with “the most vulnerable” being more likely to be assaulted, investigators found. Research available on the perpetrators of assault found them to most often be white males, typically with criminal histories, regardless of whether they were a fellow resident or employed as direct care staff.

Fifty percent of the victims included in the studies died within a year of an assault occurring.

While the review was unable to determine the prevalence of assault incidents in nursing homes, the annual rate of staff-on-resident assault was found to be less than 1%. Sexual assault is one of the least common forms of elder abuse, researchers said, but it often goes “greatly underreported” due to barriers such as state regulations, limited staff resources and training, limited evidence and victims’ conditions.

“Although sexual assault is among one of the most shocking types of assault, it is also the least acknowledged, detected, and reported type of assault against nursing home residents,” the study reads. Undertrained staff or failure to follow protocol often hamper investigations, researchers said.

“Much more needs to be done for this vulnerable group of people,” said lead researcher Daisy Smith. “Regulatory investigative personnel remain poorly equipped to appropriately identify and respond to sexual assault.”