Trichomoniasis (sometimes called "trich") is an infection caused by the parasite Trichomonas vaginalis. This one-celled organism infects the vagina and glands of the lower genital tract. It is passed from one person to another during sexual contact.

Many people with this sexually transmitted disease have no symptoms, but they may still transmit the infection to a sexual partner.

Vaginal infection causes a thin, irritating discharge with an unpleasant odor. The vaginal tissues may feel raw and itchy. There may be a burning sensation when urinating or having sex.

The antibiotic metronidazole is used to treat trich. This drug can be given as a single high dose or as a lower dose taken over seven days. Side effects include nausea, headache, and a metallic taste. People taking this drug must not drink alcohol for 72 hours after treatment to avoid moderate to severe nausea and vomiting. The usual dose of metronidazole cures about 90% of people with trich.

The two most common reasons treatment fails:

• The person taking the drug did not complete all the antibiotics they were prescribed
• The person becomes reinfected by a sexual partner who still has trich

For the best chance of a successful treatment, avoid sexual intercourse for one week after both partners are treated.

If the standard dose does not work, a longer course of treatment with a higher dose is prescribed. Side effects tend to be more severe with higher doses. Or, the doctor may prescribe another drug called tinidazole.

In rare instances, when infection does not go away after these treatments, special testing can determine what other medication options are needed. This often requires a consultation with an infectious disease specialist.