THE FACTS

Chlamydia is a sexually transmitted infection caused by a bacterium, Chlamydia trachomatis.

* More than 4 million Americans are infected annually, most of them sexually active adolescents and young adults.

* Most men with chlamydia have a burning sensation while urinating or a discharge from the penis; some men have no symptoms.

* In men, infection sometimes spreads to the epididymis (a tube that carries sperm from the testis), causing pain and fever.

* Most women with chlamydia have no symptoms. A minority have a burning sensation while urinating or a vaginal discharge. Women in whom the infection spreads to the uterus and Fallopian tubes sometimes have lower abdominal pain, nausea or fever.

* In women, chlamydia can lead to infection of the uterus and Fallopian tubes (pelvic inflammatory disease). Scarring of Fallopian tubes by chlamydia frequently causes infertility and increases the risk of a dangerous ectopic pregnancy (pregnancy outside the uterus).

* Women infected during pregnancy may deliver prematurely or may spread chlamydia to their infant, causing eye infection or pneumonia.

* New urine tests available at a doctor’s office or health clinic are more convenient and more accurate than cultures and other methods. These tests detect tiny amounts of genetic material (DNA or RNA) from chlamydia bacteria. They can also be used to test a discharge from a woman’s cervix.

* Various antibiotics are effective. Standard regimens include a single, one-gram dose of azithromycin or seven days’ treatment with doxycycline, 100 milligrams twice a day. Alternatives include ofloxacin, erythromycin and sulfisoxazole.