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.

To prevent reinfection with the organism that causes trichomoniasis, both partners should be treated. The most common treatment for trichomoniasis involves taking one megadose of metronidazole (Flagyl) or tinidazole (Tindamax). You can reduce your risk of infection by using condoms correctly every time you have sex.

Many women and most men with trichomoniasis have no symptoms, at least not at first. Trichomoniasis signs and symptoms for women include:

• An often foul-smelling vaginal discharge — which might be white, gray, yellow or green
• Genital redness, burning and itching
• Pain with urination or sexual intercourse

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

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

When to see a doctor

See your doctor if you have a foul-smelling vaginal discharge or if you have pain with urination or sexual intercourse.

Trichomoniasis is caused by a one-celled protozoan, a type of tiny parasite that travels between people during sexual intercourse. The incubation period between exposure and infection is unknown, but it's thought to range from four to 28 days.

Risk factors include having:

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

Pregnant women who have trichomoniasis might: 

• Deliver prematurely
• Have a baby with a low birth weight
• Transmit the infection to the baby as he or she passes through the birth canal

Having trichomoniasis also appears to make it easier for women to become infected with HIV, the virus that causes AIDS.

As with other sexually transmitted infections, the only way to prevent trichomoniasis is to abstain from sex. To lower your risk, use condoms correctly every time you have sex.

Trichomoniasis can be diagnosed by looking at a sample of vaginal fluid for women or urine for men under a microscope. If the parasite can be seen under the microscope, no further tests are needed. If this test isn't conclusive, tests called rapid antigen tests and nucleic acid amplification may be used.

The most common treatment for trichomoniasis, even for pregnant women, is to swallow one megadose of either metronidazole (Flagyl) or tinidazole (Tindamax). In some cases, your doctor might recommend a lower dose of metronidazole two times a day for seven days.

Both you and your partner need treatment. And you need to avoid sexual intercourse until the infection is cured, which takes about a week.

Don't drink alcohol for 24 hours after taking metronidazole or 72 hours after taking tinidazole, because it can cause severe nausea and vomiting.

Your doctor will likely want to retest you for trichomoniasis from two weeks to three months after treatment to be sure you haven't been reinfected.

Untreated, trichomoniasis can last for months to years.

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.