Trichomoniasis is a common sexually transmitted infection caused by a parasite. In women, trichomoniasis can cause a foul-smelling vaginal discharge, genital itching and painful urination.

Men who have trichomoniasis typically have no symptoms. Pregnant women who have trichomoniasis might be at higher risk of delivering their babies prematurely.

Treatment for trichomoniasis is taking an antibiotic — either metronidazole (Flagyl), tinidazole (Tindamax) or secnidazole (Solosec). To prevent being infected again, all sexual partners should be treated at the same time. You can reduce your risk of infection by using condoms correctly every time you have sex.

Most people with trichomoniasis have no signs or symptoms. However, symptoms may develop over time. When signs and symptoms develop, they are different for men and women.

In women, trichomoniasis signs and symptoms include:

• A large amount of a thin, often foul-smelling discharge from the vagina — which might be clear, white, gray, yellow or green
• Genital redness, burning and itching
• Pain with urination or sex
• Discomfort over the lower stomach area

In men, trichomoniasis rarely causes symptoms. When men do have signs and symptoms, however, they might include:

• Itching or irritation inside the penis
• Burning with urination or after ejaculation
• Discharge from the penis

See your health care provider if you have any symptoms of trichomoniasis or if you become aware that a sexual partner has the infection.

Trichomoniasis is caused by a one-celled protozoan, a type of tiny parasite called Trichomonas vaginalis. The parasite passes between people during genital contact, including vaginal, oral or anal sex. The infection can be passed between men and women, women, and sometimes men.

The parasite infects the lower genital tract. In women, this includes the outer part of the genitals (vulva), vagina, opening of the uterus (cervix) and the urinary opening (urethra). In men, the parasite infects the inside of the penis (urethra).

The time between exposure to the parasite and infection (incubation period) is unknown. But it's thought to range from four to 28 days. Even without symptoms, you or your partner can still spread the infection.

Risk factors for getting trichomoniasis include having:

• Multiple sexual partners
• A history of other sexually transmitted infections (STIs)
• A previous episode of trichomoniasis
• Sex without a condom

Pregnant women who have trichomoniasis might:

• Deliver too early (prematurely)
• Have a baby with a low birth weight
• Give the infection to the baby as the baby passes through the birth canal

Having trichomoniasis causes irritation in the genital area that may make it easier for other STIs to enter the body or to pass them to others. Trichomoniasis also appears to make it easier to become infected with human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS).

Trichomoniasis is associated with an increased risk of cervical or prostate cancer.

Untreated, trichomoniasis infection can last for months to years.

As with other sexually transmitted infections, the only way to prevent trichomoniasis is to not have sex. To lower your risk, use internal or external condoms correctly every time you have sex.

Your health care provider may diagnose trichomoniasis by doing an exam of the genitals and lab tests.

Your health care provider may also look at a sample of vaginal fluid for women or a swab from inside the penis (urethra) for men under a microscope. If the parasite can be seen under the microscope, no further tests are needed.

If the test doesn't show the parasite, but your provider thinks you may have trichomoniasis, other tests may be done. Your provider may order tests done on a sample of vaginal fluid, a penis uretheral swab or sometimes urine. Tests include a rapid antigen test and nucleic acid amplification test.

If you have trichomoniasis, your provider may also do tests for other sexually transmitted infections (STIs) so they can also be treated.

Treatment of trichomoniasis requires an oral antibiotic that is effective against infections caused by this parasite. Treatment can be given during pregnancy. Options may include:

• Megadose. Your health care provider may recommend one large dose (megadose) of either metronidazole (Flagyl), tinidazole (Tindamax) or secnidazole (Solosec). You only take these oral medications one time.
• Multiple doses. Your provider might recommend several lower doses of metronidazole or tinidazole. You take the pills two times a day for seven days. To help clear up the infection completely, keep taking this medicine for the full time your provider prescribed the drug, even if you begin to feel better after a few days. If you stop using this medicine too soon, your infection may not go away completely.

All sex partners need treatment at the same time. This prevents getting the infection again right way (reinfection). And you need to avoid sex until the treatment is done and the symptoms have gone away. This usually takes about a week after finishing the last antibiotic dose. Tell your health care provider if symptoms don't go away after treatment.

Drinking alcohol during and for a few days after treatment can cause severe nausea and vomiting. Don't drink alcohol for 24 hours after taking metronidazole, 48 hours after taking secnidazole or 72 hours after taking tinidazole.

Your health care provider will typically retest you for trichomoniasis after treatment. A retest two weeks to three months after treatment can check to be sure the infection is gone and that you haven't been reinfected.

Even if you've had treatment that gets rid of trichomoniasis, it's possible to get it again if you're exposed to someone with the infection.

Your family doctor, gynecologist or a medical practitioner at an urgent care center can diagnose and prescribe treatment for trichomoniasis.

What you can do

Before the appointment, you might prepare a list that includes:

• A detailed description of your symptoms, including when they started
• Sexually transmitted infections you've had
• The number of sexual partners you've had during the past few years

What to expect from your doctor

For women, your doctor will perform a pelvic exam and may take a sample of your vaginal fluids for testing. Men will need to provide a urine sample.