Trichomoniasis is the most common nonviral sexually transmitted infection (STI). Approximately 5 million women in the United States are infected annually.[32,33] This may actually be an underestimate of the incidence of trichomoniasis. Screening methods are relatively insensitive and this infection is often not reported. It is caused by a protozoan, Trichomonas vaginalis. Infection with T vaginalis is easily transmitted sexually and is associated with an increased risk of acquiring HIV.[25,32] The mechanism of action is thought to be an increase in the vaginal secretions of CD4+ cells, which serve as target cells for the HIV virus. Furthermore, trichomoniasis infection is also associated with coinfection with other STIs.
Between 50% and 75% of trichomoniasis infections are thought to be asymptomatic. The most common symptoms are vulvar itching and increased, malodorous vaginal discharge, which is yellow-green in color. Other symptoms may include petechiae on the cervix and erythema of the vagina.
The diagnosis is usually made via wet mount microscopy that shows motile trichomonads. This method has a sensitivity rate of only 60% to 70%. This low sensitivity rate may be explained by the fact that the length of time the protozoa are motile differs from person to person, and the fact that the large amount of inflammation associated with the vaginitis may preclude the observation of the motile protozoa. In women who are suspected to have trichomoniasis (i.e., those with symptoms but no observable motile trichomonads), culture for T vaginalis is recommended. Other findings that might lead the practitioner to suspect trichomoniasis are leukocytes on microscopy and pH >4.5. The culture is more sensitive for diagnosis than any other commercially available method, but is too costly to be used as primary method for diagnosing.[25,33] As previously stated, the Affirm VP III system includes testing for trichomonads. More recently, another test has been developed and also provides quick results. The OSOM Trichomonas Rapid Test (Genzyme Corporation), recently approved for use by the US Food and Drug Administration (FDA), is an antigen-based diagnostic test. High sensitivity and specificity rates have been reported for this test.
Because the sensitivity of a wet mount is low, some women who have a negative wet mount will have trichomoniasis. In a study of 2194 women who presented for STI evaluation, Swygard et al. found that 17.5% had culture-proven trichomoniasis. Using logistic regression, they identified three characteristics that were predictive of a positive culture in women with symptoms who had a negative wet mount: contact to trichomonas, African American race, and self-reported drug use. These authors concluded that using cultures for the patients who have one of these predictive characteristics could help improve detection of trichomoniasis.
All nonpregnant women with symptomatic or asymptomatic trichomoniasis should be treated. Sexual partners should be treated as well.[1,25] The standard treatment recommended by the CDC is metronidazole 2 grams orally in a single dose or tinidazole 2 g orally in a single dose. The alternative regimen is metronidazole 500 mg twice daily for 7 days. More recently, tinidazole in a 2-gram dose has been approved by the FDA for the treatment of trichomoniasis. This drug has been used in other countries for years with good results, and has been added to the 2006 CDC recommended treatment guidelines. Treatment of women who are HIV-positive is the same as for women who are HIV-negative.
Neither topical metronidazole therapy nor therapy with other topical classes of drugs has been shown to be as efficacious in the treatment of trichomoniasis as oral therapy. The trichomonads may be found in the urinary tract as well as the crypts of the vagina, so it is reasonable that topical treatments may not work as well as systemic treatments.
In recurrent infection or in the case of treatment failure, if reinfection is excluded, the patient should be retreated with 500 mg of metronidazole orally twice per day for 7 days or tinidazole 2 g in a single dose. If this additional treatment fails, treatment with either metronidazole or tinidazole 2 g orally for 5 days is recommended. If this second regimen is not effective, providers are encouraged to consult a specialist. Susceptibility testing of T vaginalis to metronidazole and tinidazole should be done. Consultation and susceptibility testing are available from the CDC.
Recurrent infection may actually be reinfection from an untreated partner. It is very important that the practitioner emphasize the importance of partner treatment necessary to prevent reinfection.
Infection with trichomonas is associated with preterm delivery, premature rupture of the membranes, and low birth weight.[1,3] Pregnant women with trichomoniasis have a 30% higher risk of delivering a baby with low birthweight or delivering preterm than those without the infection. It is recommended that symptomatic pregnant women may be treated with a single 2-gram dose of metronidazole. Treatment may be given in any trimester. Many practitioners prefer to wait until after the first trimester to treat, even though studies have not demonstrated teratogenic problems with metronidazole use.[25,28] Although trichomoniasis is associated with preterm birth, there are no data supporting that treatment of trichomoniasis in the asymptomatic pregnant woman will decrease the incidence of preterm birth. In fact, in some cases there is evidence that treatment may be more harmful to the pregnancy than not treating. In a study done by Klebanoff et al., they found that asymptomatic pregnant women who were treated with metronidazole had a higher preterm delivery rate than those treated with placebo (19% vs. 10.7%; P = .004; RR 1.8; 95% CI 1.2-2.7). They used a nonstandard dosing of 2 grams metronidazole with a repeat dose 48 hours later. The results were surprising to the authors, and not completely understood. It is thought that the dying trichomonads could "...elicit an inflammatory response or release a virus from the organism that increases the risk of preterm birth." No studies to date have demonstrated that treatment of trichomoniasis during pregnancy has decreased poor outcomes in pregnancy. Based on this, the CDC does not currently recommend treating asymptomatic pregnant women for trichomoniasis nor do they recommend routine screening.[25,32]
J Midwifery Womens Health. 2006;51(6):423-430. © 2006 Elsevier Science, Inc.
Cite this: Etiology, Diagnosis, and Management of Vaginitis - Medscape - Nov 01, 2006.