Chlamydia is the most frequently reported bacterial sexually transmitted disease in the United States. In 2008, 1,210,523 chlamydial infections were reported to CDC from 50 states and the District of Columbia. Under-reporting is substantial because most people with chlamydia are not aware of their infections and do not seek testing. Also, testing is not often done if patients are treated for their symptoms. An estimated 2,291,000 non-institutionalized U.S. civilians ages 14-39 are infected with C. trachomatis  based on the U.S. National Health and Nutrition Examination Survey.  Women are frequently re-infected if their sex partners are not tre

Chlamydia is known as a "silent" disease because the majority of infected people have no symptoms. If symptoms do occur, they usually appear within 1 to 3 weeks after exposure.

To help prevent the serious consequences of chlamydia, screening at least annually for chlamydia is recommended for all sexually active women age 25 years and younger. An annual screening test also is recommended for older women with risk factors for chlamydia (a new sex partner or multiple sex partners). All pregnant women should have a screening test for chlamydia.