Chlamydia testing is used to screen for, diagnose, and verify successful treatment of infections caused by the bacteria Chlamydia trachomatis. Chlamydia is one of the most common bacterial sexually transmitted diseases (STD) in the U.S. and can cause serious complications if not treated. Screening for, diagnosing, and treating chlamydia is very important to prevent long-term complications and spread of the infection to others. (For more, see the "What is being tested?" section.) Photo source: CDC/James Gathany

Testing for Chlamydia trachomatis and(gonorrhea)Neisseria gonorrhoeae is often done at the same time since the infections caused by these two bacteria can have similar signs and symptoms. These bacteria may be acquired at the same time, and an an individual may have infections with both. A definitive diagnosis is important since the two infections require different antibiotic treatment. Repeat testing is recommended to ensure that treatment has been effective. This is done about three months after a person has completed treatment.

The nucleic acid amplification test (NAAT) is the recommended method of testing for chlamydia. NAAT is a molecular test that detects the genetic material (DNA) of Chlamydia trachomatis. It is generally more sensitive and specific than other chlamydia tests and can be performed on a vaginal swab on women, or urine from both men and women, which eliminates the need for a pelvic exam in women.

Besides NAAT, other chlamydia tests include culture, which grows the bacteria, direct fluorescent antibody stain (DFA), and DNA probe, but these are used less commonly since they are less sensitive to detect a chlamydia infection.

Screening

Because many infected people do not have any noticeable symptoms, a number of health organizations recommend regular screening for certain people:

Women

All sexually active women younger than age 25 and sexually active women age 25 and older who are at increased risk should get yearly screening for chlamydia, according to the Centers for Disease Control and Prevention (CDC) and the American College of Obstetricians and Gynecologists. The U.S. Preventive Services Task Force (USPSTF) and the American Academy of Pediatrics also recommend routine screening for these women (the USPSTF says age 24 and younger).

Examples of risk factors for chlamydia infection include:

• Previous chlamydia infections, even if they were treated
• Having STDs, especially HIV
• Having new or multiple sex partners
• Having a sex partner diagnosed with an STD
• Using condoms inconsistently
• Exchanging sex for money or drugs
• Using illegal drugs
• Living in a detention facility

For pregnant women, the CDC recommends screening for chlamydia during the first trimester or first prenatal visit and, for those younger than 25 or who are at increased risk of infection, repeat testing in the third trimester. Pregnant women diagnosed with chlamydia should be retested about 3 months after completing treatment. (See Pregnancy & Prenatal Testing.)

Men

The CDC recommends that men who have sex with men get chlamydia screening at least annually. Health organizations do not recommend routine screening for sexually active, heterosexual men with no symptoms. However, healthcare practitioners may recommend screening to their patients when, for example, there is a high number of cases (prevalence) of STDs in the community.

Diagnosis

Chlamydia testing may also be done when a person’s sex partner has been diagnosed with chlamydia or when a person has signs and symptoms of the infection.

For women, if symptoms occur, they may include:

• Bleeding between menstrual periods and after sexual intercourse
• Abdominal pain
• Painful intercourse
• Painful and/or frequent urination
• Abnormal vaginal discharge

For men, symptoms may include:

• Pus or milky discharge from the penis
• Painful and/or frequent urination
• Pain, tenderness and swelling of the testicles

Both men and women can get an infection in their rectum and may be tested when they have symptoms such as itching, inflammation, pain, discharge and/or bleeding from the rectum. Testing for both chlamydia and gonorrhea may be done when a newborn has symptoms of conjunctivitis, such as redness and swelling of the eye, and discharge.

Women or men treated for chlamydia should be retested three months after their treatment.

A positive test indicates an active chlamydia infection that requires treatment with a course of antibiotics.

A negative test means only that there is no evidence of infection at the time of the test. It is important for those who are at increased risk to have screening tests performed on an annual basis to check for possible infection, especially since re-infection is common, particularly among teenagers.

If you are infected, your sexual partner(s) should be tested and treated as well.

People who are infected have a higher risk of contracting other sexually transmitted diseases, including a 3 to 5 times greater risk of acquiring HIV if exposed to it.

Molecular tests are only FDA-approved for use with urine samples or samples from genital sites such as the vagina and penis; they have not been FDA-approved for performance with ocular (eye), pharyngeal (throat), or rectal samples. Individual laboratories may perform molecular testing on these samples, but they are required to validate the methods themselves.

The Centers for Disease Control and Prevention (CDC) recommends the NAAT testing method for chlamydia, except in cases of child sexual abuse in boys or rectal and oral infections in preteen girls. In these cases, culture is recommended.