The document discusses Chlamydia, one of the most common sexually transmitted diseases in the US, infecting an estimated 4.5 million people annually. Chlamydia is often asymptomatic, so many cases go undiagnosed and untreated. When symptoms do occur in women, they can include abnormal vaginal discharge or bleeding between periods. Left untreated, Chlamydia can cause permanent damage to reproductive organs. The bacteria has a two-stage life cycle that allows it to replicate within host cells.