Sexually transmitted diseases seem to be a big problem for most American girls, according to a new study by the federal Centers for Disease Control and Prevention presented Tuesday at an STD prevention conference in Chicago.

More than one in four American girls seems to be carrying at least one sexually transmitted disease, with the highest rate in African-American girls. This translates in an estimated 3.2 million U.S. girls ages 14 and 19 having a sexually transmitted infection such as human papillomavirus or HPV, chlamydia, genital herpes or trichomoniasis.

“What we found is alarming. This means that far too many young women are at risk for the serious health effects of untreated STDs, including infertility and cervical cancer,” the CDC’s Dr Sara Forhan, who led the study, told reporters, according to Reuters.

The findings were based on an analysis of 838 girls between ages 14 and 19 who participated in the 2003-2004 National Health and Nutrition Examination Survey, an annual study that assesses a broad range of health issues. By far the most common sexually transmitted disease was HPV, 18 percent, which causes not just cervical but throat and other cancers, as well as genital warts. The study authors cautioned that most people who get infected with HPV never know it, because the virus goes away on its own without causing any health problems.

The other common sexually transmitted infections are chlamydia, which affected 4 percent of the girls surveyed, trichomoniasis, which affected 2.5 percent and herpes simplex virus 2, which affected 1.9 percent.

The study also revealed that nearly half the black teens surveyed had at least one sexually transmitted infection versus 20 percent among whites and Mexican-American teens.

The researchers said figures could be slightly higher because other sexually transmitted diseases, syphilis, HIV, and gonorrhea, were not included in the study, although epidemiologists say the prevalence is low for those infections among adolescents.

“It [study] shows that what people have always suspected is true. Sexually transmitted infections have been called a hidden epidemic because a lot of these conditions are going to be asymptomatic when they're diagnosed, but they're highly common,” said Dr. Emily J. Erbelding, an infectious diseases specialist at Johns Hopkins Bayview Medical Center, according to the Boston Globe.

Health experts placed blame on inadequate sex education, from parents and from schools for the high rates of sexually transmitted diseases. They seem to focus too much on abstinence-only programs.

“This is pretty shocking. To talk about abstinence is not a bad thing, but teen girls — and boys too — need to be informed about how to protect themselves if they do have sex,” Dr. Elizabeth Alderman, an adolescent medicine specialist at Montefiore Medical Center’s Children’s Hospital in New York said.

Only about half the surveyed girls acknowledged having sex. Some teens define sex as only intercourse, yet other types of intimate behavior including oral sex can spread some diseases. Among those who admitted having sex, the rate was even more disturbing — 40 percent had an S.T.D.

Officials of the CDC said the findings underscored the need to strengthen screening, vaccination and other prevention measures for the disease, which are among the highest public health priorities.

“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.

About 19 million new sexually transmitted infections occur each year among all age groups in the United States.