NEW YORK (Reuters Health) - Within 2 years of having sex for the first time, half of teenage girls may be at least one of three common sexually transmitted infections (STIs), according to results of a study published today. Often, those girls are infected by the age of 15.

Researchers followed 386 urban adolescent girls aged 14 to 17 for up to 8 years. Within 2 years of becoming sexually active, half of the girls were infected with at least one of three common sexually transmitted organisms: Chlamydia trachomatis, Neisseria gonorrhoeae, or Trichomonas vaginalis -- the organisms that cause chlamydia, gonorrhea and trichomoniasis, respectively.

The researchers found that a quarter of the women had acquired their first STI by age 15, most often Chlamydia.

“Repeated infections were very common,” study investigator Dr. Wanzhu Tu, of Indiana University School of Medicine in Indianapolis told Reuters Health by email. “Within 4 to 6 months (depending on the organism) after treatment of the previous infection, a quarter of the women were re-infected with the same organism.”

Tu said young women are at risk of STIs as soon as they become sexually active, but recommendations are lacking about when it is appropriate to begin screening.

“These young women are vulnerable to STIs, but because of their younger age, they may not be perceived by health care providers as having STI risk, and thus are not screened in a timely manner.”

The current findings, Tu said, highlight the importance of early STI screening and treatment. “For urban adolescent women, STI screening (especially for chlamydia) should begin within 1 year after first intercourse and infected individuals should be retested frequently, preferably every 3 to 4 months,” the researcher said.

“To my knowledge, this study provides the first data on the timing of the initial STI and subsequent STIs following the onset of sexual activity in urban adolescent women,” Tu added.

The study findings appear in the latest issue of Archives of Pediatrics and Adolescent Medicine, published by the American Medical Association.

A companion paper in the journal details a program that proved successful in curbing risky sexual behavior among 15- to 21-year-old African American adolescent girls and young women.

The participants, all of whom where visiting a sexual health clinic in Atlanta, took part in two group counseling sessions and received telephone support and vouchers to give to their partners to encourage them to get tested and treated for STIs.

This study is “exciting” for several reasons, Dr. Bonita Stanton from Wayne State University in Detroit wrote in a commentary. First, the program reduced first and recurrent chlamydia infections and led to higher rates of self-reported condom use, she points out.

Second, it got the teen girls cut back on douching, which has been linked to increased risk of STIs.

But perhaps “most intriguing,” Stanton wrote, is that the young adolescent girls who participated in the program were able to convince their sexual partners to get tested for STIs.

SOURCE: Archives of Pediatrics and Adolescent Medicine, December 2009.