The transmission of chlamydia occurs during vaginal, anal, or oral sex. Transmission can also occur from an infected mother to her baby during vaginal childbirth.
Any sexually active person can be infected with chlamydia. The greater the number of sex partners, the greater the risk of infection. Chlamydia is easily confused with gonorrhea, another sexually transmitted disease (STD). Gonorrhea and chlamydia have similar symptoms and can have similar complications if not treated, but the two STDs have different treatments.
Because the cervix (opening to the uterus) of teenage girls and young women is not fully matured, they are at particularly high risk for infection if sexually active.
Since chlamydia can be transmitted by oral or anal sex, men who have sex with men are also at risk for chlamydial infection.