Many sexually assaulted teens seeking emergency room care don't receive recommended tests and prevention treatments for pregnancy and venereal disease, according to a new study.

Testing and treatment rates varied widely among 38 children's hospitals studied, from zero teens treated to almost 90 percent tested.

Subpar treatment puts teens at risk for infections including HIV, chlamydia and gonorrhea, along with unwanted pregnancies. The results highlight a need for better awareness of testing and treatment guidelines from the American Academy of Pediatrics and federal Centers for Disease Control and Prevention, the study authors said. Their report, based on 2004-13 data on almost 13,000 teens treated, was published Monday in Pediatrics. Here are some details:

ASSAULT RATES

Teen sexual assault is more common than some might think. Up to 25 percent of U.S. girls and 10 percent of boys are sexually abused or assaulted by the age of 18, the researchers said. Almost 11 percent of high school girls and 4 percent of boys reported having been raped in a 2013 government survey. Studies suggest these rates have been mostly stable in recent years.

WHAT'S RECOMMENDED?

The CDC and pediatricians recommend testing sexually assaulted teens for several venereal diseases and giving preventive antibiotics for chlamydia and gonorrhea. Other advice includes testing for hepatitis B in unvaccinated patients and for HIV and syphilis in areas where those diseases are prevalent, and providing pregnancy tests and emergency contraception.

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COMPLIANCE

On average 44 percent of assaulted teens got recommended tests and about one-third got preventive treatment, according to the study, led by researchers at the Children's Hospital of Philadelphia who analyzed information from a childrens' hospitals database. Rates for both varied by hospital and were lowest for younger patients.

Other studies have found low emergency room testing and treatment rates for sexually assaulted adults, for whom CDC has similar guidelines.

EXPLANATIONS

Some teens may not have been tested or treated because the assault didn't involve intercourse. Also, some hospitals might not test teens who delay seeking care, but most experts recommend doing so anyway to detect pre-existing and new infections, the researchers say. A Pediatrics editorial notes that some teens may decline testing and treatment, or may seek care in outpatient clinics, so the true rates of under-treatment are unknown.

THE ADVICE

The researchers recommend standardizing medical care for sexually assaulted teens, along with guidelines awareness. In addition, doctors need to identify and address barriers to providing these patients appropriate medical care, the editorial says.