Chlamydia infection is the most common sexually transmitted disease, responsible for a record 1.1 million cases reported to the Centers for Disease Control and Prevention in 2007, and experts there estimate that twice that many cases go undetected. Left untreated, chlamydia can cause infertility or potentially fatal ectopic pregnancies. But many women aren’t even aware that they were exposed to it—possibly years ago—until they try to have a baby and can’t.

Chlamydia can be detected with a simple urine test. It can be treated with a single dose of antibiotics, and the CDC has been urging all sexually active women under 26 years old to be tested for it annually, as well as older women who have had a change of sexual partner. Yet fewer than 40 % of women in those categories are being screened.

Even when women are treated for chlamydia, about 25% become reinfected within six months—probably due to a partner who wasn’t treated. So the CDC recommends that doctors give women a second course of antibiotics for their partners, even without being seen by a doctor themselves. It can be treated either with a weekly dose of doxycycline or a single dose of azithromycin, which goes by the brand name Zithromax, made by Pfizer Inc., in many countries.

Most official efforts are focused on detecting active chlamydia infections in young women. But what if you think you were exposed years ago? The main risk is to fertility. The CDC recommends that all pregnant women be tested for chlamydia at the first prenatal visit, although if you are planning to become pregnant, it’s a good idea to be tested for all STDs well in advance. Older women who are experiencing pelvic pain, intermittent bleeding, unusual vaginal discharge or signs of early menopause should ask their doctor if chlamydia could be involved.

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