More than 1.1 million chlamydia cases were reported in 2007, with the rate among women three times that of men. And yet less than half of U.S. women are being screened for one of the nation’s most common sexually transmitted infections (STI), warns the Centers for Disease Control and Prevention (CDC).

Experts link the low screening rates to the fact that chlamydia causes few or no symptoms and that women may assume their blood tests and Pap smears automatically test for STIs.

Chlamydia, a bacteria, is spread through oral, vaginal and anal sex. Left untreated, it can cause serious problems, such as pelvic inflammatory disease, burning during urination, infertility and chronic pain.

Women, especially young women, are more susceptible. The CDC recommends yearly screenings for all sexually active women 25 or younger as well as all pregnant women and all older women who have a new sex partner or multiple sex partners (you can be infected more than once). Men should be tested as well, since chlamydia affects them too.

Talk to a health care provider about a urine or swab test.