Article courtesy of the NIAID:

Chlamydial (“kla-mid-ee-uhl”) infection is the most common bacterial sexually transmitted disease (STD) in the United States today. The U.S. Centers for Disease Control and Prevention estimates that more than 4 million new cases occur each year. The highest rates of chlamydial infection are in 15 to 19-year-old adolescents regardless of demographics or location. Pelvic inflammatory disease (PID), a serious complication of chlamydial infection, has emerged as a major cause of infertility among women of childbearing age. Chlamydial infection is caused by a bacterium, Chlamydia trachomatis, and can be transmitted during vaginal, oral, or anal sexual contact with an infected partner. A pregnant woman may pass the infection to her newborn during delivery, with subsequent neonatal eye infection or pneumonia. The annual cost of chlamydial infection is estimated to exceed $2 billion.


Most chlamydial infections are silent, causing no symptoms. However, men and women with C. trachomatis may experience abnormal genital discharge or pain during urination. These early symptoms may be mild. If symptoms occur, they usually appear within one to three weeks after exposure. Two of every three infected women and one or two of every four infected men have no symptoms whatsoever. As a result, often the disease may not be diagnosed and treated until complications develop.

Doctors estimate that, in women, one-third of the chlamydial infections result in PID. Often these infections are not diagnosed until PID or other complications develop. In men, rarely, chlamydial infections may lead to pain or swelling in the scrotal area, which is a sign of epididymitis, an inflammation of a part of the male reproductive system located near the testicles. Left untreated, this condition, like PID in women, can cause infertility.

C. trachomatis can cause proctitis (inflamed rectum) and conjunctivitis (inflammation of the lining of the eye). The bacteria also have been found in the throat as a result of oral sexual contact with an infected partner. In tropical climates, a particular strain of C. trachomatis causes an STD called lymphogranuloma venereum (LGV), which is characterized by prominent swelling and inflammation of the lymph nodes in the groin. Complications may follow if LGV is not treated; this infection is very rare in the United States.


Chlamydial infection can be confused with gonorrhea because the symptoms of both diseases are similar; in some populations they occur together. The most reliable way to diagnose chlamydial infection is for a clinician to send a sample of secretions from the patient’s genital area to a laboratory that will look for the organism using one of a wide variety of quick and inexpensive laboratory tests. Although attempting to grow the organism in specialized tissue culture in the laboratory is one of the most definitive tests, it is expensive and technically difficult to do, and test results are not available for three or more days.

Scientists have developed several rapid tests for diagnosing chlamydial infection that use sophisticated techniques and a dye to detect bacterial proteins. Although these tests are slightly less accurate, they are less expensive, more rapid, and can be performed during a routine checkup. These tests use a process called DNA amplification to detect the genes of the organisms in genital secretions. Recently, the U.S. Food and Drug Administration approved this process for detection of C. trachomatis in urine. This is a major step in diagnosing chlamydial infection because it does not require an invasive sample; it can be used in settings where performing a pelvic examination is not convenient or not feasible, e.g., in college health units and at health fairs. Results from the urine test are available within 24 hours.


Doctors usually prescribe antibiotics such as a one-day course of azithromycin or a seven-day course of doxycycline to treat chlamydial infection. Other antibiotics such as erythromycin or ofloxacin also are effective. Pregnant women can be treated with azithromycin or erythromycin. Amoxicillin is also a safe alternative for treating pregnant women. Penicillin, which is often used for treating some other STDs, is not effective against chlamydial infections. New medications are being developed that should greatly simplify treatment and help control the spread of C. trachomatis in the population.

A person with chlamydial infection should be sure to take all of the prescribed medication, even after symptoms disappear. If the symptoms do not disappear within one to two weeks after finishing the medicine, the patient should make a follow-up visit to the doctor or clinic. All sex partners of a person with chlamydial infection should be tested and treated to prevent reinfection and further spread of the disease.

Pelvic Inflammatory Disease

Each year up to 1 million women in the United States develop PID, a serious infection of the reproductive organs. As many as half of all cases of PID may be due to chlamydial infection, and many of these occur without symptoms. PID can result in scarring of the fallopian tubes, which can block the tubes and prevent fertilization from taking place. An estimated 100,000 women each year become infertile as a result of PID.

In other cases, scarring may interfere with the passage of the fertilized egg down into the uterus. When this happens, the egg may implant in the fallopian tube. This is called ectopic or tubal pregnancy. This is life-threatening for the mother and results in the loss of the fetus. PID is the most common cause of pregnancy-related death among poor teenagers in the inner cites and rural areas of the United States. The annual cost estimates exceed $7 billion.

Effects of Chlamydial Infection in Newborns

A baby who is exposed to C. trachomatis in the birth canal during delivery may develop conjunctivitis (eye infection) or pneumonia. Symptoms of conjunctivitis, which include discharge and swollen eyelids, usually develop within the first 10 days of life. Symptoms of pneumonia, including a progressively worsening cough and congestion, most often develop within three to six weeks of birth. Both conditions can be treated successfully with antibiotics. Because of these risks to the newborn, many doctors recommend routine testing of all pregnant women for chlamydial infection.


Because chlamydial infection often occurs without symptoms, people who are infected may unknowingly infect their sex partners. Many doctors recommend that all persons who have more than one sex partner, especially women under 25 years of age, be tested for chlamydial infection regularly, even in the absence of symptoms. Using condoms or diaphragms during sexual intercourse may help reduce the transmission of chlamydia.


NIAID researchers are working on two strategies to prevent infection: topical microbicides and a vaccine. Scientists also are looking for better ways to treat people with chlamydial infection. In addition, developing simple, inexpensive tests to diagnose chlamydial infection remains one of the most urgent research priorities.

Scientists also are studying the basic process of how C. trachomatis causes disease in the body and why some people suffer more severe complications than others. These studies may lead to insights about how to recognize women at risk for PID and PID-related infertility or other complications of chlamydial infection.

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