Trichomoniasis (aka "trich") is a sexually transmitted disease caused by a flagellated protozoan (Trichomonas vaginalis). Infection in men generally produces no symptoms (occasionally there is penile discharge and/or burning during urination). Half of infected women may also experience no symptoms (but left untreated, the infection can progress to pelvic inflammatory disease). Women's symptoms include vaginal itching, profuse yellowish-green vaginal discharge, redness of the vulva and/or vagina, painful intercourse, abdominal pain, and painful urination. Symptoms occur 4-28 days after infection. The risk of transmission is can be lowered by using barrier birth control methods such as condoms or diaphragms. A woman's risk of contracting trich increases if she is taking birth control pills, is pregnant, has just finished a menstrual period, or has another STD. The disease may also be transmitted by sharing towels and similar damp items.Medication (usually a single dose of metronidazole) is effective for curing the disease, which infects 2-3 million Americans each year.