About three-quarters of women infected with chlamydia have no symptoms. Although it is easily cured if treated early, when left untreated, the infection can lead to a host of medical problems, including infertility.
The CDC report also noted a rise in gonorrhea and syphilis.
The CDC releases the "STD Surveillance Report" each year, detailing trends in the detection of chlamydia, gonorrhea and syphilis, all caused by sexually transmitted bacteria.
In 2006, Chlamydia was the most prevalent of the three, with 1,031,000 cases were reported last year, up from 976,000 in 2005. Before that, gonorrhea held the national record, with 1,013,436 cases reported in 1978.
Women were diagnosed with chlamydia three times more often than men, a disparity the CDC attributed to the tendency of women to get tested more often.
In fact, the report stated that the overall rise in all three infections could be due to the greater prevalence, and accuracy, of STD tests. However, it added, it could also reflect an actual rise in morbidity rates.
There were 358,366 cases of gonorrhea reported in the United States in 2006, up from 339,593 in 2005 and just over 330,000 the year prior.
Although syphilis, a potentially deadly disease, has become relatively rare in the United States, there were approximately 37,000 cases reported in 2006, up from 22,288 in 2005.
