WASHINGTON (Reuters) - Half of all young Americans will get a sexually transmitted disease by the age of 25, perhaps because they are ignorant about protection or embarrassed to ask for it, according to several reports issued on Tuesday.

The reports, publicized by two nonprofit sexual and youth health groups, said there were 9 million new cases of STD among teens and young adults aged 15 to 24 in 2000.

They said the U.S. government's policy of preferring abstinence-only education would only increase those rates.

"For the 27 million young Americans under the age of 25 who have had sex, the stakes are simply too high to talk only about abstinence," James Wagoner, president of Advocates for Youth, said in a statement.

"Given the prevalence of STDs, young people need all the facts - including medically accurate information on condoms."

The reports, released jointly by Advocates for Youth -- a nonprofit group promoting sex education -- and the sexual health-oriented Alan Guttmacher Institute, pull together information from several different publications.

They include a report by the Centers for Disease Control and Prevention in the latest issue of the journal Perspectives on Sexual and Reproductive Health, and a University of North Carolina report based on interviews with teens and young adults.

"Approximately 18.9 million new cases of STD occurred in 2000, of which 9.1 million (48%) were among persons aged 15 to 24," the CDC report reads.

It said three diseases - human papillomavirus, trichomoniasis, and chlamydia - accounted for 88% of all new cases of STDs in 15- to 24-year-olds.

The CDC report did not comment on potential causes, but the Guttmacher Institute did.

"It is not surprising that teens and young adults contract a disproportionate number of infections," said Guttmacher's Sharon Camp. "Most young people are sexually active, and many are ill equipped to prevent STDs or seek testing and treatment."

She said sex education that includes information on condoms is vital to preventing STDs.

"Although abstaining from sexual activity is guaranteed to prevent STDs, some adolescents and virtually all young adults will eventually choose to have sex," Camp said.

"Before they do, they need realistic sex education that teaches them how to prevent STDs and unwanted pregnancies. It is essential to have medically accurate information about condoms and other contraceptive methods, and guidance on how to access appropriate prevention, testing and treatment services."

Teens 15 and older who have had sex have the highest STD rates of any age group in the country, and the United States has the highest STD rate of any industrialized country, according to CDC and World Health Organization figures.

The University of North Carolina report attacked federal policies that encourage abstinence-only education. "Abstinence is, of course, the only 100% effective prevention strategy," Shawn Carney, a 17-year-old member of the UNC youth panel, said in a statement.

"But with 70% of young people having sex by the age of 18, we need to hear about more than abstinence. We need to know how to prevent STDs when we do have sex later in life."

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