Urethritis in men and urethritis and cervicitis in women make up a group of infections that are linked to one organism: Chlamydia trachomatis. These chlamydial infections are the most common sexually transmitted diseases in the United States, affecting an estimated 4 million Americans each year.

Trachoma inclusion conjunctivitis, a chlamydial infection that occurs rarely in the United States, is a leading cause of blindness in third world countries. Lymphogranuloma venereum, a rare disease in the United States, is also caused by C. trachomatis.

Untreated, chlamydial infections can lead to such complications as acute epididymitis, salpingitis, pelvic inflammatory disease and, eventually, sterility. Some studies show that chlamydial infections in pregnant women are associated with spontaneous abortion and premature delivery. Other studies haven’t confirmed these findings.