Chlamydia. Chlamydia is a common sexually transmitted disease (STD) caused by the bacterium, Chlamydia trachomatis, which can harm a woman's reproductive organs. Even though symptoms of chlamydia are usually mild or absent, it can cause serious complications like infertility.Some women may not even know they have chlamydia.hlamydia is a common sexually transmitted disease (STD) caused by the bacterium, Chlamydia trachomatis, which can harm a woman's reproductive organs. Even though symptoms of chlamydia are usually mild or absent, it can cause serious complications like infertility. Some women may not even know they have chlamydia.