Management of Persistent and Recurrent Trichomonas
9/1/2015 - Christine R. Isaacs, MD
Editor: David Chelmow, MD
Trichomonas vaginalis (T. vaginalis) is a protozoan parasite. It is one of the most common sexually transmitted infections, with an estimated 3.1% prevalence in the United States. Risks for infection include being female, African American, lower education level, and living in poverty.
Transmission of trichomonas occurs through sexual contact. Many women have minimal or no symptoms. Those with symptoms often complain of vulvar or vaginal irritation, malodorous yellow-green vaginal discharge, or pruritis.
The diagnosis may be made through observation of unicellular, oval, motile parasites on saline microscopy of vaginal or urethral secretions (“wet mount”). The sensitivity of this method is only 55-60%. A number of point of care tests detecting antigens or nucleic acids have been FDA-cleared. They have sensitivities of >83% and specificities of >97%, significantly higher than microscopy. Culture can also be performed and may be useful in the setting of patients where infection is suspected, but not confirmed by microscopy.
Nitroimidazoles (metronidazole and tinidazole in the U.S.) are the only approved drugs for treatment of trichomonas and must be given orally (usually 2 gram single dose, or alternatively metronidazole 500 mg twice daily for 7 days) or parenterally. Topically applied therapy (e.g. metronidazole gel) is not effective. Due to disulfuram-like side effects, patients should be advised to avoid consuming alcohol for 24 hours after taking metronidazole or 72 hours after tinidazole.
Most women who present with continued or recurrent vaginal symptoms are likely to have been reinfected by exposure to an untreated partner. Rates of reinfection are as high as 17%. When repeat exposure is suspected, repeating the basic treatment regimen should be adequate. Patients should be instructed to abstain from sex until their sex partner(s) have completed therapy and both patient and partner are asymptomatic. Because of this high rate of reinfection, repeat screening for reinfection at 3 months in high risk patients is reasonable.
Some recurrent infections may be from organisms with decreased sensitivity to nitroimidazoles. This has been identified in 2-5% of vaginal trichomoniasis cases. High-level antimicrobial resistance also rarely occurs. If decreased sensitivity is expected, metronidazole should be administered 500mg orally twice a day for 7 days. If this fails, extended high dose therapy with metronidazole or tinidazole 2 grams orally for 5 days should be considered.
In rare cases where infection persists despite extended treatment regimens, consultation and susceptibility testing is available through the CDC (telephone: 404-718-4141; website: http://www.cdc.gov/std). While there are no evidence based guidelines to guide treatment of male partners of women with nitroimidazole treatment failure, the CDC recommends male partner evaluation and treatment with either a single dose of tinidazole 2g or metronidazole 500mg orally twice a day for 7 days.
Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines. MMWR 2015;64 (No. RR 3): 72-75. Available at: https://www.cdc.gov/std/tg2015/default.htm
ACOG Practice Bulletin. Clinical management guidelines for obstetrician-gynecologists, Number 72, May 2006: Vaginitis., Obstet Gynecol 2006;107:1195–1206.
Initial approval January 2015; Reaffirmed September 2016, Revised January 2018.
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