Parasite (T. vaginalis)
~50% women, most men
Yes, single antibiotic course
No
Trichomoniasis ('trich') is caused by Trichomonas vaginalis, a single-celled protozoan parasite, not a bacterium or virus. It is the most common curable non-viral STI worldwide, with an estimated 156 million new infections a year. It infects the vagina and urethra; it does not establish infection in the throat or rectum, so its routes are essentially genital. Infection is far more common, and more often symptomatic, in women than in men, in whom it is frequently transient and silent. Although easily cured, untreated trichomoniasis increases susceptibility to HIV.
Vaginal sex (the main route; from men it transmits efficiently to women)
Vulva-to-vulva contact and shared genital fluids
Sharing sex toys without cleaning
Does not infect the mouth or rectum; oral and anal routes are not significant
Many people, especially men, have no symptoms
Frothy, yellow-green vaginal discharge with an unpleasant smell
Genital itching, soreness, or redness
Pain or burning when urinating
Discomfort during sex
Trichomoniasis is reliably cured with a course of metronidazole or tinidazole (antibiotics that work against the parasite). All recent sexual partners should be treated at the same time to avoid passing it back and forth, and sex should be avoided until everyone has completed treatment.