THURSDAY, July 6 (HealthDay News) -- Only 38 percent of teen and young adult sexual assault victims who were prescribed antiviral medications to prevent HIV infection returned for follow-up visits to medical centers, a new report finds.

Only 15 percent of these young assault victims completed drug therapy that could help them ward off HIV infection, added the researchers, who reported the findings in the July issue of the journal Archives of Pediatrics & Adolescent Medicine.

In the study, Boston University School of Medicine researchers reviewed the charts of 145 females, ages 12 to 22, treated at two pediatric emergency departments in Boston within 72 hours of being sexually assaulted.

Of those patients, 129 (89 percent) were offered medications to prevent HIV infection and 110 (76) agreed to take the drugs. Of the latter group, 86 were referred for follow-up treatment, but only 38 percent of them returned for at least one follow-up visit and 15 percent completed the full 28 days of preventive treatment, the study said.

The researchers said their findings highlight the difficulty associated with prescribing HIV-prevention therapies to young sexual assault victims and determining which patients require preventive therapy.

"In many cases of adolescent sexual assault, the risks of HIV transmission cannot be determined," the authors wrote. "Among patients in our study, 21 percent reported having blacked out during the assault, 54 percent were unsure whether ejaculation had occurred, and 27 percent were unsure whether a condom had been used."

The researchers added that many teen sexual assault victims have psychiatric conditions that could decrease the likelihood that they'll adhere to HIV-prevention therapy.

"We agree with published recommendations that post-exposure prophylaxis be offered to adolescent sexual assault survivors for exposures that pose a risk of HIV transmission," the study authors concluded.