Chlamydia is the most frequently reported bacterial sexually transmitted disease (STD) in the United States. In 2002, 834,555 chlamydial infections were reported to the Centers for Disease Control (CDC) from 50 states and the District of Columbia (Washington, D.C.).
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 2.8 million Americans are infected with chlamydia each year. Women are frequently reinfected if their sex partners are not treated.