At least one in four teenage girls in the US has a sexually transmitted disease, according to a new study.
A survey by the US Centre for Disease Control and Prevention suggested that more than 3 million teenagers aged 14 to 19 had at least one STD.
A virus that causes cervical cancer is by far the most common sexually transmitted infection in girls aged 14 to 19, while the highest overall prevalence is among African American girls - nearly half of those studied had at least one STD.
That rate compared with 20% among both whites and Mexican-American teenagers.
About half of those surveyed acknowledged ever having sex; among them, the rate was 40%. While some defined sex as only intercourse, other types of intimate behaviour including oral sex can spread some infections.
The results follow a survey of 838 girls for a US government health survey. They were tested for four infections. Human papillomavirus, or HPV, which can cause cervical cancer, was found in 18% of those studied.
Chlamydia affected 4%; trichomoniasis, 2.5%; and herpes was found in 2%.
Dr John Douglas, director of the CDC's division of STD prevention, said the results were the first to examine the combined US national prevalence of common sexually transmitted diseases among adolescent girls.
'High STD rates among young women, particularly African-American young women, are clear signs that we must continue developing ways to reach those most at risk,' Mr Douglas said.