This microorganism, with its four flagella to propel it, is not a normal inhabitant of the vagina.

When present, it causes a profuse, frothy white or greenish vaginal discharge.

When the discharge is suspended in normal saline and examined under the microscope, the typical movement of these large organisms (larger than white blood cells) is obvious. Itching may be present, but this is inconsistent.

Treatment*

Treatment reduces symptoms and signs of T. vaginalis infection and might reduce transmission. Likelihood of adverse outcomes in women with HIV also is reduced with T. vaginalis therapy.

Alcohol consumption should be avoided during treatment with nitroimidazoles. To reduce the possibility of a disulfiram-like reaction, abstinence from alcohol use should continue for 24 hours after completion of metronidazole or 72 hours after completion of tinidazole.

The nitroimidazoles are the only class of antimicrobial medications known to be effective against T. vaginalis infections. Of these drugs, metronidazole and tinidazole have been cleared by FDA for the oral or parenteral treatment of trichomoniasis. Tinidazole is generally more expensive, reaches higher levels in serum and the genitourinary tract, has a longer half-life than metronidazole (12.5 hours versus 7.3 hours), and has fewer gastrointestinal side effects. In randomized clinical trials, recommended metronidazole regimens have resulted in cure rates of approximately 84%–98%, and the recommended tinidazole regimen has resulted in cure rates of approximately 92%–100%. Randomized controlled trials comparing single 2 g doses of metronidazole and tinidazole suggest that tinidazole is equivalent or superior to metronidazole in achieving parasitologic cure and resolution of symptoms.

Metronidazole gel does not reach therapeutic levels in the urethra and perivaginal glands. Because it is less efficacious than oral metronidazole, it is not recommended.

Other Management Considerations

Providers should advise persons infected with T. vaginalis to abstain from sex until they and their sex partners are treated (i.e., when therapy has been completed and any symptoms have resolved). Testing for other STDs including HIV should be performed in persons infected with T vaginalis.

Follow-up

Because of the high rate of reinfection among women treated for trichomoniasis (17% within 3 months in one study), retesting for T. vaginalis is recommended for all sexually active women within 3 months following initial treatment regardless of whether they believe their sex partners were treated (see Diagnostic Considerations). Testing by nucleic acid amplification can be conducted as soon as 2 weeks after treatment. Data are insufficient to support retesting men.

Management of Sex Partners

Concurrent treatment of all sex partners is critical for symptomatic relief, microbiologic cure, and prevention of transmission and reinfections. Current partners should be referred for presumptive therapy to avoid reinfection. Partners should be advised to abstain from intercourse until they and their sex partners have been adequately treated and any symptoms have resolved. EPT might have a role in partner management for trichomoniasis and can be used in states where permissible by law; however, no one partner management intervention has been shown to be superior in reducing reinfection rates. Though no definitive data exist to guide treatment for partners of persons with persistent or recurrent trichomoniasis in whom nonadherance and reinfection are unlikely, partners benefit from undergoing evaluation and receiving the same regimen as the patient (see Persistent or Recurrent Trichomoniasis).

Persistent or Recurrent Trichomoniasis

Persistent or recurrent infection caused by antimicrobial-resistant T. vaginalis or other causes should be distinguished from the possibility of reinfection from an untreated sex partner. Although most recurrent T. vaginalis infections are thought to result from reinfection, some infections might be attributed to antimicrobial resistance. Metronidazole resistance occurs in 4%–10% of cases of vaginal trichomoniasis, and tinidazole resistance in 1%.

In general, T. vaginalis isolates have lower minimum lethal concentrations to tinidazole than metronidazole. Emerging nitroimidazole-resistant trichomoniasis is concerning, because few alternatives to standard therapy exist. Single-dose therapy should be avoided for treating recurrent trichomoniasis that is not likely a result of reinfection.

If treatment failure has occurred with metronidazole 2 g single dose and reinfection is excluded, the patient (and their partner[s]) can be treated with metronidazole 500 mg orally twice daily for 7 days. If this regimen fails, clinicians should consider treatment with metronidazole or tinidazole at 2 g orally for 7 days. If several 1-week regimens have failed in a person who is unlikely to have nonadherence or reinfection, testing of the organism for metronidazole and tinidazole susceptibility is recommended.

CDC has experience with susceptibility testing for nitroimidazole-resistant T. vaginalis and treatment management of infected persons and can provide assistance (telephone: 404–718–4141; website: http://www.cdc.gov/std). Higher dose tinidazole at 2–3g for 14 days, often in combination with intravaginal tinidazole, can be considered in cases of nitroimidazole-resistant infections; however, such cases should be managed in consultation with an expert.

Alternative regimens might be effective but have not been systematically evaluated; therefore, consultation with an infectious-disease specialist is recommended. The most anecdotal experience has been with intravaginal paromomycin in combination with high-dose tinidazole; clinical improvement has been reported with other alternative regimens including intravaginal boric acid and nitazoxanide. The following topically applied agents have shown minimal success (<50%) and are not recommended: intravaginal betadine (povidone-iodine), clotrimazole, acetic acid, furazolidone, gentian violet, nonoxynol-9, and potassium permanganate. No other topical microbicide has been shown to be effective against trichomoniasis.

Special Considerations

Allergy, Intolerance, and Adverse Reactions

Metronidazole and tinidazole are both nitroimidazoles. Patients with an IgE mediated-type allergy to a nitroimidazole can be managed by metronidazole desensitization according to a published regimen and in consultation with a specialist.

Pregnancy

T. vaginalis infection in pregnant women is associated with adverse pregnancy outcomes, particularly premature rupture of membranes, preterm delivery, and delivery of a low birthweight infant. Although metronidazole treatment produces parasitologic cure, certain trials have shown no significant difference in perinatal morbidity following metronidazole treatment.

One trial suggested the possibility of increased preterm delivery in women with T. vaginalis infection who received metronidazole treatment, yet study limitations prevented definitive conclusions regarding the risks of treatment.

More recent, larger studies have shown no positive or negative association between metronidazole use during pregnancy and adverse outcomes of pregnancy).

If treatment is considered, the recommended regimen in pregnant women is metronidazole 2 g orally in a single dose. Symptomatic pregnant women, regardless of pregnancy stage, should be tested and considered for treatment. Treatment of T. vaginalis infection can relieve symptoms of vaginal discharge in pregnant women and reduce sexual transmission to partners. Although perinatal transmission of trichomoniasis is uncommon, treatment also might prevent respiratory or genital infection of the newborn. Clinicians should counsel symptomatic pregnant women with trichomoniasis regarding the potential risks for and benefits of treatment and about the importance of partner treatment and condom use in the prevention of sexual transmission.

The benefit of routine screening for T. vaginalis in asymptomatic pregnant women has not been established. However, screening at the first prenatal visit and prompt treatment, as appropriate, are recommended for pregnant women with HIV infection, because T. vaginalis infection is a risk factor for vertical transmission of HIV. Pregnant women with HIV who are treated for T. vaginalis infection should be retested 3 months after treatment.

Although metronidazole crosses the placenta, data suggest that it poses a low risk to pregnant women. No evidence of teratogenicity or mutagenic effects in infants has been found in multiple cross-sectional and cohort studies of pregnant women. Women can be treated with 2 g metronidazole in a single dose at any stage of pregnancy.

Metronidazole is secreted in breast milk. With maternal oral therapy, breastfed infants receive metronidazole in doses that are lower than those used to treat infections in infants, although the active metabolite adds to the total infant exposure. Plasma levels of the drug and metabolite are measurable, but remain less than maternal plasma levels (http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?LACT). Although several reported case series found no evidence of adverse effects in infants exposed to metronidazole in breast milk, some clinicians advise deferring breastfeeding for 12–24 hours following maternal treatment with a single 2-g dose of metronidazole. Maternal treatment with metronidazole (400 mg three times daily for 7 days) produced a lower concentration in breast milk and was considered compatible with breastfeeding over longer periods of time.

Data from studies involving human subjects are limited regarding use of tinidazole in pregnancy; however, animal data suggest this drug poses moderate risk. Thus, tinidazole should be avoided in pregnant women, and breastfeeding should be deferred for 72 hours following a single 2-g dose of tinidazole (http://toxnet.nlm.nih.gov/newtoxnet/lactmed.htm).

*CDC 2015 STD Treatment Guidelines