The good news is that American teenagers are less likely to have sex today than 10 years ago.

The bad news is, one in four girls between the ages of 14 and 19 has at least one sexually transmitted disease, which adds up to more than 3 million girls nationally.

Those are startling statistics -- and for African-American girls in that age group, the news gets even worse: Half of them have a sexually transmitted disease. The STD study was done by the Atlanta-based federal Centers for Disease Control and Prevention. Advocates for Youth, a national sex education organization, reported the other study -- that teens are having less sex than a decade ago.

Maybe so, but given the CDC report, the danger to teens of having sex appears to be greater than ever.

Sex-education groups usually use bad news about sex to urge sexually active teens to use condoms. The primary purpose should be to discourage teens from being sexually active.

Start by being sure they understand that condoms are not 100-percent effective in preventing pregnancy, much less in preventing infection.

For instance, the most common infection girls get from having sex is the human papilloma virus, or HPV -- which often leads to cervical cancer. Yet condoms are only about 20 percent effective in preventing HPV. That's scary, and underlines the need for teachers and parents -- especially parents who should take the lead in these matters -- to stress to kids that abstinence is the only sure way to avoid dangerous sexual infections.

To encourage the notion that condoms can be a safety net is misleading, to say the least. At best, condoms reduce the odds of getting sick from having sex, but only someone bent on self- destruction would find a 20 percent HPV preventive rate an acceptable risk.

High disease rates among teenagers points up the benefits of abstinence. Indeed, those rates demonstrate that sex outside of marriage is unsafe. If this fact can be hammered home to our young people, then hopefully the trend of fewer teens having sex soon will translate into fewer teens getting sick from sex.