Chlamydia trachomatis is a gram-negative bacterium that infects the columnar epithelium of the cervix, urethra, and rectum, as well as nongenital sites such as the lungs and eyes. The bacterium is the cause of the most frequently reported sexually transmitted disease in the United States, which is responsible for more than 1 million infections annually. Most persons with this infection are asymptomatic. Untreated infection can result in serious complications such as pelvic inflammatory disease, infertility, and ectopic pregnancy in women, and epididymitis and orchitis in men. Men and women can experience chlamydia-induced reactive arthritis.

Screening is recommended in all women younger than 25 years, in all pregnant women, and in women who are at increased risk of infection. Screening is not currently recommended in men. In neonates and infants, the bacterium can cause conjunctivitis and pneumonia. Adults may also experience conjunctivitis caused by chlamydia. Trachoma is a recurrent ocular infection caused by chlamydia and is endemic in the developing world.

Chlamydia trachomatis is a gram-negative bacterium that infects the columnar epithelium of the cervix, urethra, and rectum, as well as nongenital sites. The bacterium is the cause of the most frequently reported sexually transmitted disease in the United States,1 and is the leading cause of infectious blindness in the world.2 According to the Centers for Disease Control and Prevention (CDC) in 2009, the rate of sexually transmitted chlamydia infections in the United States was 426 cases per population of 100,000, which represents a 24 percent increase in the rate of infection since 2006.3 More recent data from 2010 indicates that 1,307,893 chlamydia infections were reported to the CDC from all 50 states and the District of Columbia.4 The CDC estimates that there are 2.8 million chlamydia cases in the United States annually—more than twice the number actually reported.5 This is an increase of 5 percent over the past year, and 27 percent from four years ago.5 From 2000 to 2010, the chlamydia screening rate among young women nearly doubled, from 25 to 48 percent.5