To diagnose an infection with the parasite Trichomonas vaginalis, which causes the sexually transmitted disease trichomoniasis
When a woman has symptoms of infection, such as a foul-smelling vaginal discharge, genital itching, and/or pain during urination, or when a man has genital itching or irritation, burning after urination or ejaculation, and/or a discharge from the penis
For men or women, the initial portion of urine stream (first-catch urine sample); or in women, a swab of fluid and cells from the vagina or cervix; or in men, a swab from the tube that carries urine from the bladder to outside the body (urethra).
Trichomonas vaginalis is a single cell (protozoan) parasite that cannot be seen by the naked eye (microscopic). It causes vaginal infections in women and, in men, infections of the urethra, the tube that carries urine from the bladder to outside the body, and inflammation of the prostate (prostatitis). Trichomonas testing detects the parasite in samples from the vagina or penis to diagnose an infection.
According to the Centers for Disease Control and Prevention (CDC), trichomoniasis, which is caused by the infection, is one of the most common, curable sexually transmitted diseases (STDs). In the U.S., an estimated 3.7 million people have the infection, but only about 30% develop any symptoms. Symptoms are more common in women than in men.
Trichomonas vaginalis is one of the most common causes of vaginitis (inflammation of the vagina) in women. When they occur, symptoms include:
- Itching, irritation, soreness of the vagina, or a burning sensation
- Frothy, yellow-green or grey vaginal discharge
- Foul-smelling vaginal discharge
- Frequent urge to urinate
- Possible blood-spotting from the vagina
- Itching of inner thighs
- Discomfort during intercourse
In men, symptoms may include:
- Burning after urinating or ejaculating
- Itching or irritation of the urethra
- Discharge from the urethra
These symptoms may take 5 to 28 days after exposure to an infected person or longer to develop; however, once diagnosed, trichomoniasis is easily treated with prescription antibiotics. During treatment, an infected person should cease sexual activity and inform partners so that they can also be treated and prevent re-infection.
For women, a healthcare practitioner may use a swab or small brush to collect a sample of cells or secretion from the vagina during a pelvic examination. Sometimes, the sample may be obtained from the collection vial used for a Pap smear.
Urine is recommended for men, but can also be used for women. As you begin to urinate, collect the initial portion of your urine stream (first-catch) in a container provided by the healthcare practitioner or laboratory.
Sometimes for men, a healthcare practitioner may use a swab or brush to collect a sample of cells or secretion from the urethra.
No test preparation is needed.
- How is it used?
The test is used to diagnose a sexually transmitted infection with the parasite Trichomonas vaginalis (T. vaginalis). Secretions from the vagina (for women) or urethra (for men) are tested by one of the following methods:
Molecular testing, direct DNA probes, or nucleic acid amplification tests (NAATs)—NAATs are the most sensitive tests for T.vaginalis and are now considered the gold standard for diagnosing it. With some NAATs, samples collected for testing of gonorrhea and chlamydial infections can also be used to test for T. vaginalis. Most NAATs can be used with both vaginal and urine samples for women. Only some are approved for use with samples from men.
Samples from women can be obtained during a routine gynecologic examination that includes a Pap smear. However, T. vaginalis found incidentally during a Pap smear is not considered diagnostic because false positives and false negatives may occur.
- Wet prep—the sample is placed on a slide and examined under a microscope for the presence of the parasite. The wet prep is performed on secretions that are freshly obtained and examined promptly under the microscope without the aid of any special stains. This test has poor sensitivity, especially for samples from men. The Centers for Disease Control and Prevention (CDC) recommends following up with a more sensitive test (i.e., molecular testing or culture) when trichomoniasis is suspected but not confirmed by wet prep.
- Culture—this test is very sensitive and specific but requires up to 7 days to allow sufficient numbers of the parasite to grow and be detected.
- Other methods—these include the direct fluorescent antibody (DFA) test and a test that detects trichomonas antigens.
- Molecular testing, direct DNA probes, or nucleic acid amplification tests (NAATs)—NAATs are the most sensitive tests for T.vaginalis and are now considered the gold standard for diagnosing it. With some NAATs, samples collected for testing of gonorrhea and chlamydial infections can also be used to test for T. vaginalis. Most NAATs can be used with both vaginal and urine samples for women. Only some are approved for use with samples from men.
- When is it ordered?
A healthcare practitioner may order a test for T. vaginalis when someone complains of symptoms. For women, symptoms may include vaginal itching, burning, or a foul-smelling vaginal discharge. For men, symptoms may include pain when urinating or discharge from the urethra. It is not possible to diagnose trichomoniasis based on symptoms alone.
If someone has an infection with another sexually transmitted disease (STD), the healthcare practitioner might order Trichomonas testing as well. Likewise, if results indicate that a person is infected with T. vaginalis, the person may also be tested for chlamydia and gonorrhea since these STDs often occur together.
The Centers for Disease Control and Prevention (CDC) recommend that sexually active women treated for trichomoniasis be retested within 3 months due to the possibility of reinfection by an untreated partner.
- What does the test result mean?
A positive test indicates an infection with T. vaginalis that requires treatment with a course of prescription medication. If someone is infected, their sexual partner(s) should also be tested and treated as well.
A negative test means either there is no infection with T. vaginalis and symptoms are due to another cause or the parasite was not able to be detected in the sample using the test method performed. If trichomoniasis is still suspected, a different testing method may be used to confirm the result.
- Is there anything else I should know?
An infected person is at greater risk of getting other sexually transmitted diseases. The genital inflammation that occurs with trichomoniasis can increase a woman's susceptibility to HIV infection and to pelvic inflammatory disease.
Neonatal trichomoniasis, though rare, can occur, causing complications in the newborn.
Fecal contamination of the specimen may show a non-pathogenic organism (Pentatrichomonas hominis, formally known as Trichomonas hominis) that is similar in appearance and may be confused with T. vaginalis through direct observation. The presence of this organism does not require treatment.
- Should I tell my partner that I have trichomoniasis?
Yes, you should tell your sexual partner(s) that you have trichomoniasis so that they can get tested and treated.
- How long does it take to get results?
This will depend on the test method used to diagnose the infection. If physical exam, history or symptoms suggest trichomoniasis, your healthcare practitioner will most likely perform a wet prep and check it under a microscope to look for the parasite. There is also a rapid test that can detect trichomonas antigens in 10 minutes.
However, other methods that require your sample to be sent to a laboratory may take longer to get results. A culture method is available that involves a self-contained pouch system for the detection of T. vaginalis. Results from this method may be available within 24 to 72 hours. A conventional culture can take up to 7 days, while some molecular methods can produce results in under an hour.
- What complications can occur if the infection is not properly treated?
Untreated or improperly treated trichomoniasis can result in an infection that can increase the risk of pelvic inflammatory disease (PID) and cervical neoplasia - a possible precursor to cervical cancer - in women. Pregnant women with trichomoniasis are at higher risk for having pre-term or low birth weight babies. Men are sometimes asymptomatic, resulting in chronic infection and re-infection of partner(s). In men, infection may lead to inflammation of the urethra and chronic prostatitis. In both men and women, trichomoniasis is a risk factor for HIV and is associated with infertility.
- How can trichomoniasis be prevented?
The most reliable ways to avoid infection with Trichomonas or any sexually transmitted disease (STD) are to abstain from oral, vaginal, and anal sex or to be in a long-term, mutually monogamous relationship with an uninfected partner. People who are sexually active should correctly and consistently use condoms to reduce the risk of trichomoniasis and other STDs.
- Where can I get tested?
Visit the CDC webpage Get Tested. You can input your zip code and find a local testing site.
- How is trichomoniasis treated?
Your healthcare practitioner can prescribe medications to treat trichomoniasis. Your sexual partner(s) should also be treated. You should refrain from having sex for 7- 10 days after you and your partner have been treated. Get tested again if your symptoms come back.
- If I get treated, can I get trichomoniasis again?
Yes. Even though treatment will cure your infection, you can get it again if you are exposed again. In fact, about one in five people get reinfected within 3 months after receiving treatment, according to the Centers for Disease Control and Prevention.