The first national study of four common sexually transmitted diseases among girls and young women has found that one in four are infected with at least one of the diseases, federal health officials reported Tuesday.
Nearly half the African-Americans in the study of teenagers ages 14 to 19 were infected with at least one of the diseases monitored in the study -- human papillomavirus (HPV), chlamydia, genital herpes and trichomoniasis, a common parasite.
The 50 percent figure compared with 20 percent of white teenagers, health officials and researchers said at a news conference at a scientific meeting in Chicago.
The two most common sexually transmitted diseases, or S.T.D.'s, among all the participants tested were HPV, at 18 percent, and chlamydia, at 4 percent, according to the analysis, part of the National Health and Nutrition Examination Survey.
Each disease can be serious in its own way. HPV, for example, can cause cancer and genital warts.
Among the infected women, 15 percent had more than one of the diseases.
Women may be unaware they are infected. But the diseases, which are infections caused by bacteria, viruses and parasites, can produce acute symptoms like irritating vaginal discharge, painful pelvic inflammatory disease and potentially fatal ectopic pregnancy. The infections can also lead to longterm ailments like infertility and cervical cancer.
The survey tested for specific HPV strains linked to genital warts and cervical cancer.
Officials of the Centers for Disease Control and Prevention said the findings underscored the need to strengthen screening, vaccination and other prevention measures for the diseases, which are among the highest public health priorities.
About 19 million new sexually transmitted infections occur each year among all age groups in the United States.
''High S.T.D. infection rates among young women, particularly young African-American women, are clear signs that we must continue developing ways to reach those most at risk,'' said Dr. John M. Douglas Jr., who directs the centers' division of S.T.D. prevention.
The president of the Planned Parenthood Federation of America, Cecile Richards, said the new findings ''emphasize the need for real comprehensive sex education.''
''The national policy of promoting abstinence-only programs is a $1.5 billion failure,'' Ms. Richards said, ''and teenage girls are paying the real price.''
Although earlier annual surveys have tested for a single sexually transmitted disease in a specified population, this is the first time the national study has collected data on all the most common sexual diseases in adolescent women at the same time. It is also the first time the study measured human papillomavirus.
Dr. Douglas said that because the new survey was based on direct testing, it was more reliable than analyses derived from data that doctors and clinics sent to the diseases center through state and local health departments.
''What we found is alarming,'' said Dr. Sara Forhan, a researcher at the centers and the lead author of the study.
Dr. Forhan added that the study showed ''how fast the S.T.D. prevalence appears.''
''Far too many young women are at risk for the serious health effects of untreated S.T.D.'s, '' she said.
The centers conducts the annual study, which asks a representative sample of the household population a wide range of health questions. The analysis was based on information collected in the 2003-4 survey.
Extrapolating from the findings, Dr. Forhan said 3.2 million teenage women were infected with at least one of the four diseases.
The 838 participants in the study were chosen at random with standard statistical techniques. Of the women asked, 96 percent agreed to submit vaginal swabs for testing.
The findings and specific treatment recommendations were available to the participants calling a password-protected telephone line. Three reminders were sent to participants who did not call.
Health officials recommend treatment for all sex partners of individuals diagnosed with curable sexually transmitted diseases. One promising approach to reach that goal is for doctors who treat infected women to provide or prescribe the same treatment for their partners, Dr. Douglas said. The goal is to encourage men who may not have a physician or who have no symptoms and may be reluctant to seek care to be treated without a doctor's visit.
He also urged infected women to be retested three months after treatment to detect possible reinfection and to treat it.
Dr. Forhan said she did not know how many participants received their test results.
Federal health officials recommend annual screening tests to detect chlamydia for sexually active women younger than 25. The disease agency also recommends that women ages 11 to 26 be fully vaccinated against HPV.
The Food and Drug Administration has said in a report that latex condoms are ''highly effective'' at preventing infection by chlamydia, trichomoniasis, H.I.V., gonorrhea and hepatitis B.
The agency noted that condoms seemed less effective against genital herpes and syphilis. Protection against human papillomavirus ''is partial at best,'' the report said.