My son and his girlfriend are expecting a baby in five months. His girlfriend was diagnosed with chlamydia, and the doctors have scared her about the baby being born blind or with other problems. They started her on amoxicillin, but she has yet to tell my son that he needs to start treatment. Can something bad happen to the baby now? Will something bad happen to the baby even after treatment? How long does it take to be cured of this STD?

C.G.

Chlamydia trachomatis is one of the most common sexually transmitted infections. In adults, this bacterium causes several conditions, including urethritis (inflammation of the urethra, the tube that carries urine from the bladder) in men and infection of the cervix (the neck of the uterus, or womb) in women. It can lead to infertility in women due to damage to the fallopian tubes that lead from the uterus to the ovaries. Chlamydia also can cause several types of eye infections, including ocular trachoma, considered to be the most common cause of preventable blindness in the world. Trachoma is spread by contact with fingers, flies and inanimate objects contaminated with the organism. In this disease, which occurs mainly in the underdeveloped world, there is chronic and recurrent infection of the conjunctivae, the membranes lining the front of the eyes and inside the eyelids. This leads to scarring of the lids and eventually results in damage to the cornea and blindness.

In the United States and the rest of the developed world, chlamydial eye infection typically results in conjunctivitis, inflammation of the conjunctivae, also called "pink eye." The inflammation is usually not very severe, involving -- like conjunctivitis due to other causes, such as viral infections -- redness and a mild discharge. Unlike viral conjunctivitis, however, it typically involves only one eye and, without treatment, can take several weeks to resolve. In some cases, there can be scarring of the cornea as seen with early trachoma. However, even without treatment, most cases resolve without permanent effects.

When an infant is born to a mother infected with chlamydia, there is about a 25 percent chance that he or she will develop neonatal (newborn) conjunctivitis. This condition usually develops about a week after birth, but occasionally the onset is delayed. It is very similar to the disease that develops in adults, and like the adult form, it also usually resolves, even without treatment. Sometimes, however, as in the adult form, it can result in permanent scarring.

Treatment of conjunctivitis in newborns involves oral erythromycin. Although topical antibiotics can clear up the eye infection, oral treatment is necessary to eradicate the organism from the body -- an important consideration because chlamydia can also cause pneumonia. Preventing the infection in the first place is the best strategy, however. One protective measure routinely performed in the United States, placing antibiotic ointment in the eyes of newborns, is effective in preventing eye infections caused by gonorrhea bacteria but is not particularly helpful in defending against chlamydia.

The most effective way to protect babies is to screen expectant mothers and treat those found to be infected. Women with genital chlamydia infections usually have no symptoms, so all pregnant women probably should be screened. Treating the mother with antibiotics is about 90 percent effective in preventing disease in the baby. Without treatment, however, the infection can persist through the entire pregnancy. Furthermore, since no treatment is 100 percent effective, repeated testing should be performed to ensure that the infection is eradicated. Erythromycin is considered the drug of choice for pregnant women with chlamydia infection; for women who cannot tolerate erythromycin, amoxicillin (Amoxil) can be given for 14 days. Your son also should be treated, regardless of whether he has symptoms.