Chlamydia is the most common STD in the U.S. today, with as many as 4 million new cases each year. It causes about half the known cases of NGU (non-gonococcal urethritis) in men. It breeds on the cervix in women. The symptoms are often mild, and frequently go unnoticed. They are the same symptoms as for gonorrhea and can be confused with it. However, they appear a little later, within 1 to 3 weeks of sexual contact. More rarely, Chlamydia can be passed by a hand infected with the discharge from parent to baby.

If left untreated, chlamydia can lead to PID and infertility. Tests involve taking swabs from the cervix and culturing a specimen. The antibiotic of choice is tetracycline. Protect the cervix.