Chlamydia infection is caused by the organism Chlamydia trachomatis. It is the most common sexually transmitted disease in the United States. Sexually active individuals and individuals with multiple partners are at highest risk.

Chlamydia may be acquired jointly with gonorrhea and/or syphilis, so individuals with one sexually transmitted disease must be screened for other sexually transmitted diseases as well. Untreated chlamydia can lead to pelvic infection and infertility.

In men, chlamydia may produce symptoms similar to those of gonorrhea (discharge from penis or rectum, burning on urination or defecation), and can also cause epididymitis and orchitis. However, up to 25% of infected men may have no symptoms.

Chlamydia (female): only approximately 30% of women will have symptoms due to chlamydia -- hence screening sexually active women for chlamydia is necessary to diagnose and treat asymptomatic women in order to decrease the risk of developing complications. Women who do have symptoms may note vaginal discharge, burning on urination, or abdominal pain.

Untreated infection may lead to pelvic inflammatory disease (PID), which can cause scarring of the fallopian tubes and result in infertility. Tubal scarring also increases the likelihood of an ectopic pregnancy (tubal pregnancy).

If a women is infected with chlamydia while pregnant, the infection can cause premature labor and delivery. In addition, the infant may develop chlamydial conjunctivitis (eye infection) and chlamydial pneumonia.