Chlamydia is a curable sexually transmitted infection (STI) caused by a bacterium (a kind of germ) called Chlamydia trachomatis. Chlamydia can infect the urethra (water passage), the uterus (womb), the cervix (neck of womb), the ovarian (Fallopian) tubes, testicles, rectum (back passage), throat and eyes. Most men and women infected with chlamydia will not notice anything wrong. Prompt treatment is recommended to prevent more serious problems.