Many teenage girls diagnosed with the sexually transmitted disease chlamydia become reinfected over the next year, according to a large study of students attending school health centers.

Researchers found that of 897 girls who tested positive for chlamydia at a school-based health center, about one quarter were reinfected over the following year. Middle-school students were at greatest risk, with a reinfection rate of 39 percent, the researchers report in the journal Sexually Transmitted Diseases.

It’s estimated that more than 2 million Americans between the ages of 14 and 39 are infected with Chlamydia trachomatis, a bacterial STD that can be cured with antibiotics. When the infection is untreated, it can spread into the uterus and fallopian tubes, sometimes leading to chronic pelvic pain, pelvic inflammatory disease and infertility.

Because chlamydia often causes no symptoms or only mild ones, experts recommend that all sexually active women age 25 or younger be tested for the infection once a year.

Those who test positive should be tested again 3 months later to catch any repeat infection.

The current findings underscore the importance of frequently re-testing in adolescents, especially when there is a history of chlamydia, according to the researchers, led by Dr. Charlotte A. Gaydos of Johns Hopkins University in Baltimore. The results also suggest that school-based health clinics are a good place to offer these tests.

Their study included 10,600 girls, who were tested for chlamydia between 1996 and 2003 at one of 11 Baltimore school-based health centers located in 8 high schools and 3 middle schools.

Each year, between 15 percent and 20 percent of girls tested positive for the STD. And in any given year, about 25 percent of these students were reinfected when follow-up tests were within the next 12 months.

About 18,000 U.S. schools currently have health centers that provide physical and mental health services to students who want them. Most are operated by a local hospital, health department or other community health center.

The centers in the study currently treat girls who have chlamydia infection, counsel them on how to lower their STD risk, give them condoms, and notify the students’ partners that they should be tested.

School health centers, the authors conclude, stand as an important weapon in controlling STD rates among adolescents.

“Schools represent a logical forum for students to access health services,” the researchers write. “The installation of additional school-based health centers should be encouraged, along with school-wide screening programs for sexually active students.”

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SOURCE: Sexually Transmitted Diseases, March 2008.