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Chlamydia is a curable sexually transmitted disease(STD). You can get chlamydial infection during vaginal, oral, or anal sexual contact with an infected partner. Even though symptoms of chlamydia are usually mild or absent, serious complications that cause irreversible damage, including infertility, can occur "silently" before a woman ever recognizes a problem. Chlamydia also can cause discharge from the penis of an infected man. Chlamydia is one of the most widespread bacterial STDs in the United States.

C. trachomatis inclusion bodies; Magnified 200X. Source: CDC PHIL/ Dr. E. Arum, Dr. N. Jacobs



Chlamydia trachomatis bacteria live in vaginal fluid and in semen. About 70 percent of chlamydial infections have no symptoms, thereby naming it the "silent" disease. Symptoms usually appear within 1 to 3 weeks after the infection occurs. Those who do have symptoms may have an abnormal discharge (mucus or pus) from the vagina or penis or experience pain while urinating. These early symptoms may be very mild.

The bacterial infection may move inside the body if it is not treated.

In men, bacteria can infect the urinary tract and the epididymis, causing epididymitis (inflammation of the reproductive area near the testicles).


Chlamydia is caused by infection with the bacteria called Chlamydia trachomatis. Although C. trachomatis is the most widely known of the Chlamydia genus, it has three species that cause human disease:

  • C. psittaci, which can cause pneumonia (psittacosis).

All species of Chlamydia are small obligate intracellular parasites, and, because of this, were once considered to be viruses. However, we now know they are bacteria. Although they are unique in lacking peptidoglycan—a component of the cell wall in other bacteria and the site of action of many antibiotics, including penicillins.


Chlamydia is easily confused with gonorrhea because the symptoms of both diseases are similar and the diseases can occur at the same time.

File:10026 Chlamydia.jpg
CDC photograph showing biologist, Damian Danavall, preparing a molecular test that can differentiate between four sexually transmitted organisms known to be the cause for vaginal and urethral discharges.

There are laboratory tests to diagnose chlamydia. Some can be performed on urine, while other tests require that a specimen be collected from a site such as the penis or cervix. The preferred method of testing currently is the molecular test also known as nucleic acid amplification tests (NAAT). This test is based on amplification of the DNA that is present in C. trachomatis. Molecular testing for C. trachomatis is currently the standard and is widely utilized. The advantage of molecular tests is that they are generally more sensitive and specific than conventional culture and can therefore identify more positive specimens. All positive molecular tests for C. trachomatis should be verified by the same or another methodology for confirmation.

Testing for Neisseria gonorrhoeae (gonorrhea) and Chlamydia trachomatis is generally done simultaneously as the two organisms have similar clinical presentations.


C. trachomatis can be treated with an antibiotic such as azithromycin (taken for one day) or doxycycline (taken for 7 days). Or, you might get a prescription for another antibiotic such as erythromycin or ofloxacin.

Health care providers may treat pregnant women with azithromycin, erythromycin, or sometimes with amoxicillin. Penicillin, which health care providers often use to treat some other STDs, won't cure chlamydia.

The following precautions are recommended for people diagnosed with chlamydia:

  • Take all medicine, even after symptoms disappear, for the amount of time prescribed
  • Undergo re-evaluation if symptoms do not disappear within 1 to 2 weeks after finishing all medicine
  • Avoid sex until treatment is completed and successful
  • Tell all sex partners so they can be tested and treated

These steps help avoid being reinfected with the bacteria. Repeated infections increase the risk for reproductive complications.

For updated information on treatment for chlamydia, read the CDC's Sexually Transmitted Diseases Treatment Guidelines.


The surest way to avoid transmission of STDs is to abstain from sexual contact or be in a long-term mutually monogamous relationship with a partner who has been tested and is not infected.

Using latex condoms correctly and consistently during vaginal or rectal sexual activity reduces the risk of getting chlamydia and developing complications.

Health care experts recommend all sexually active women 25 years of age and younger get chlamydia screening tests annually. They recommend an annual screening test for older women with risk factors for chlamydia (a new sex partner or many sex partners). In addition, all pregnant women are advised to have a screening test for chlamydia.

How Chlamydia is Spread

Chlamydia can be transmitted during vaginal, anal, or oral sex. Chlamydia can also be passed from an infected mother to her baby during vaginal childbirth.

Any sexually active person can be infected with chlamydia. The greater the number of sex partners, the greater the risk of infection. Because the cervix (opening to the uterus) of teenage girls and young women is not fully matured and is probably more susceptible to infection, they are at particularly high risk for infection if sexually active. Since chlamydia can be transmitted by oral or anal sex, men who have sex with men are also at risk for chlamydial infection.

Related Problems


Chlamydia and Pelvic Inflammatory Disease]]

In women, chlamydial infections, which are usually asymptomatic, may result in pelvic inflammatory disease(PID), which is a major cause of infertility, ectopic pregnancy, and chronic pelvic pain. As with other inflammatory STDs, chlamydial infection can facilitate the transmission of HIV infection. In addition, pregnant women infected with chlamydia can pass the infection to their infants during delivery, potentially resulting in neonatal conjunctivitis and pneumonia. Due to the large burden of disease and risks associated with infection, CDC recommends screening all sexually active women younger than 26 years of age for chlamydia annually.[1]

Each year, up to 1 million women in the United States develop pelvic inflammatory disease (PID), a serious infection of the reproductive organs. Twenty to forty percent of women with chlamydial infections that are not adequately treated may develop PID.

PID can cause scarring of the fallopian tubes, which can block the tubes and prevent fertilization from taking place. Researchers estimate that 100,000 women each year become infertile because of PID.

In other cases, scarring may interfere with the passage of the fertilized egg to the uterus during pregnancy. When this happens, the egg may attach itself to the fallopian tube. This is called ectopic or tubal pregnancy. This very serious condition can result in miscarriage and can cause death of the mother.

In men, untreated chlamydia may lead to pain or swelling in the scrotal area. This is a sign of inflammation of the epididymis. Though complications in men are rare, infections can cause pain, fever, and sterility.

Complications in newborns

A baby who is exposed to C. trachomatis in the birth canal during delivery may develop an eye infection or pneumonia. Symptoms of an eye infection, called conjunctivitis or "pink eye," include discharge in the eye and swollen eyelids and usually develop within the first 10 days of life.

Symptoms of pneumonia, including a cough that gets steadily worse and congestion, most often develop within 3 to 6 weeks of birth. Health care providers can treat both conditions successfully with antibiotics.

Because of these risks to the newborn, many providers recommend that all pregnant women get tested for chlamydia as part of their prenatal care.

Related disorders

Lymphogranuloma Venereum (LGV)

Lymphogranuloma venereum (LGV) is a systemic, sexually transmitted disease (STD) caused by a type of Chlamydia trachomatis that rarely occurs in the United States or other industrialized countries. However, the Netherlands[2] and other European countries have reported increases in LGV proctitis among men who have sex with men (MSM). The majority of patients with LGV proctitis in the U.S. have been HIV-infected MSM.

Symptoms of LGV include:


Trachoma is the result of infection of the eye with Chlamydia trachomatis. Infection spreads from person to person, and is frequently passed from child to child and from child to mother, especially where there are shortages of water, numerous flies, and crowded living conditions.

Infection often begins during infancy or childhood and can become chronic. If left untreated, the infection eventually causes the eyelid to turn inwards, which in turn causes the eyelashes to rub on the eyeball, resulting in intense pain and scarring of the front of the eye. This ultimately leads to irreversible blindness, typically between 30 and 40 years of age.

This patient presented with conjunctivitis, which proved to be a consequence of Reiter's syndrome. Reiter’s syndrome consists of a predominately 3 symptoms, which include arthritis, conjunctivitis, and urinary tract infections or urethritis. Usually the disease begins in a region of an existing infection due to bacteria such as C. trachomatis. Source: CDC.

Reiter's Syndrome

Reiter's syndrome is a disorder that causes three seemingly unrelated symptoms: arthritis, redness of the eyes, and urinary tract symptoms.

Doctors sometimes refer to Reiter's syndrome as a seronegative spondyloarthropathy because it is one of a group of disorders that cause inflammation throughout the body, particularly in parts of the spine and at other joints where tendons attach to bones. (Examples of other seronegative spondyloarthropathies include psoriatic arthritis, ankylosing spondylitis, and inflammatory bowel syndrome arthritis.) Inflammation is a characteristic reaction of tissues to injury or disease and is marked by four signs: swelling, redness, heat, and pain.

Reiter's syndrome is also referred to as reactive arthritis, which means that the arthritis occurs as a "reaction" to an infection that started elsewhere in the body. In many patients, the infection begins in the genitourinary tract (bladder, urethra, penis, or vagina). The infection is most commonly passed from one person to another by sexual intercourse. This form of the disorder is sometimes called genitourinary or urogenital Reiter's syndrome. Another form of the disorder, called enteric or gastrointestinal Reiter's syndrome, develops when a person eats food or handles substances that are tainted with bacteria. [3]

Clinical Trials

For a list of ongoing and upcoming trials related to chlamydia, click here


Scientists are looking for better ways to diagnose, treat, and prevent chlamydia. Scientists supported by the National Institute of Allergy and Infectious Diseases recently determined the complete genome (genetic blueprint) for C. trachomatis. The genome represents an encyclopedia of information about the bacteria. This accomplishment will give scientists important information as they try to develop a safe and effective vaccine.

Researchers also are focusing on developing topical microbicides (preparations that can be inserted into the vagina to prevent infection) that are effective and easy for women to use.



C. trachomatis infections are the most commonly-reported notifiable disease in the United States. They are among the most prevalent of all STDs and, since 1994, have comprised the largest proportion of all STDs reported to CDC[4]. Recent studies also demonstrate the high prevalence of chlamydial infections in the general U.S. population. From 1999 to 2002, chlamydia prevalence in those aged 14-39 years was 2.2%.[5] Among young adults (18-26 years of age) chlamydia prevalence was estimated to be 4.2%.[6]

The increase in reported chlamydial infections during the last 10 years reflects the expansion of chlamydia screening activities, use of increasingly sensitive diagnostic tests, an increased emphasis on case reporting from providers and laboratories, improvements in the information systems for reporting, and, possibly, true increases in disease. However, many women who are at risk are still not being tested, reflecting, in part, lack of awareness among some health care providers and limited resources available to support screening.

In 2000, for the first time, all 50 states and the District of Columbia had regulations requiring the reporting of chlamydia cases.

In 2006, 1,030,911 chlamydial infections were reported to CDC from 50 states and the District of Columbia.[4] The reported number of chlamydial infections was almost three times the number of reported cases of gonorrhea (358,366 gonorrhea cases were reported in 2006).[4]

In 2006, chlamydia rates increased for all racial and ethnic groups except Asian/Pacific Islanders. The rate of chlamydia among African Americans was over eight times higher than that of whites.[4] The rates among American Indian/Alaska Natives (797.3) and Hispanics (477.0) were also higher than that of whites (5.2 and 3.1 times higher, respectively).


  1. Centers for Disease Control and Prevention. Sexually Transmitted Diseases Treatment Guidelines, 2006. MMWR. 2006;55(No.RR-11):38. Full Text
  2. Centers for Disease Control and Prevention. Lymphogranuloma Venereum Among Men Who Have Sex with Men --- Netherlands, 2003--2004, 2004 MMWR 53(42);985-988 Full Text
  3. Barth WF, Segal K. Reactive arthritis (Reiter's syndrome). Am Fam Physician. 1999 Aug;60(2):499-503, 507. Abstract Full Text
  4. 4.0 4.1 4.2 4.3 Centers for Disease Control and Prevention. National STD Report 2006.Full Text
  5. Datta SD, Sternberg M, Johnson RE, Berman S, et al. Gonorrhea and chlamydia in the United States among persons 14 to 39 years of age, 1999 to 2002. Ann Intern Med 2007;147(2):89-96.Abstract | Full Text
  6. Miller WC, Ford CA, Morris M, Handcock MD, Schmitz JL, et al. Prevalence of chlamydial and gonococcal infections among young adults in the United States. JAMA 2004;291(18): 2229-36.Abstract | Full Text

External Links

Centers for Disease Control and Prevention: Chlamydia

CDC National Prevention Information Network (NPIN): STDs

Office on Women's Health: Search Chlamydia

American Social Health Association: Home Page

San Francisco City Clinic: Chlamydia

The American College of Obstetricians and Gynecologists: Gonorrhea, Chlamydia and Syphilis

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