Chlamydia is a sexually transmitted disease (STD) caused by a bacteria called Chlamydia trachomatis and can infect both men and women. People who have chlamydia may not have any symptoms and can still pass the infection on to others. Common symptoms of infection can include vaginal or penile discharge, a burning sensation when urinating, or pain and swelling in one or both testicles (for men) and pain during intercourse (for women). If chlamydia is not treated, it can cause pelvic inflammatory disease and infertility problems for women. Chlamydia is easily treated with antibiotics, usually azithromycin or doxycycline.