Current Issue

2016, Volume 26, Number 1

Nucleic Acid Testing for Trichomonas vaginalis

Danny Wiedbrauk, Ph.D., Scientific Director, Virology and Molecular Biology, Warde Medical Laboratory


Trichomonas vaginalis affects men and womenTrichomoniasis is a persistent disease of the genitourinary tract caused by the flagellated protozoan Trichomonas vaginalis. Trichomoniasis is the most common nonviral sexually transmitted disease (STD) in the United States, affecting an estimated 3.7 million people (1). The overall prevalence of T. vaginalis infection is >11% in women aged ≥40 years (2). In symptomatic women who visit STD clinics, the reported prevalence is 26% (3) and in one study of incarcerated individuals, the infection rates were 9%–32% for women and 2-9% for men.

Symptoms

Seventy to eighty-five percent of T. vaginalis- infected individuals have minimal or no symptoms and when left untreated, these infections can last for months to years. (4-7) Symptomatic women can present with vaginitis with small petechial or sometimes punctate red “strawberry” spots and profuse, thin, foamy, greenish-yellow discharge with foul odor. The disease may also cause cystitis or urethritis.  Vulvar involvement is variable. In men, T. vaginalis can cause urethritis, epididymitis, or prostatitis. These infections cause 5-10% of non-gonococcal urethritis in men. (8)

Complications

Trichomonas vaginalis infection is associated with adverse pregnancy outcomes including premature rupture of membranes, preterm delivery, and delivery of a low birthweight infant. (9-12) Infection is also associated with two- to threefold increased risk for HIV acquisition. (13-16) Among women with HIV, T. vaginalis infection is associated with increased risk for pelvic inflammatory disease (17-19) and routine screening of asymptomatic women with HIV infection is recommended because of the adverse events associated with trichomoniasis and HIV infection.

Transmission/Prevention

Although partners might be unaware of their infection, organisms are readily passed between sex partners during penile-vaginal sex. (8)  Partners of men who have been circumcised might have a somewhat reduced risk of T. vaginalis infection acquisition. (20, 21) There is no vaccine for trichomoniasis, and for sexually active individuals, the best way to prevent trichomoniasis is through consistent and correct use of condoms during all penile-vaginal sexual encounters. (22)

Persistent or Recurrent Infection

While most recurrent T. vaginalis infections are thought to result from reinfection, some infections can be attributed to antimicrobial resistance. Metronidazole resistance occurs in 4%–10% of cases of vaginal trichomoniasis (23, 24)  and tinidazole resistance in 1%. (24) Emerging nitroimidazole-resistant trichomoniasis is concerning because few alternatives to standard therapy exist. The Centers for Disease Control and Infection (CDC) has experience with susceptibility testing for nitroimidazole-resistant T. vaginalis and can provide Nucleic Acid Testing for Trichomonas vaginalis treatment assistance in these cases (telephone: 404-718-4141; website: http://www.cdc.gov/std)

holding hands: T. vaginalis infections are STDsWho Should be Tested?

As mentioned previously, the CDC recommends routine screening of asymptomatic women with HIV infection because of the adverse events associated with trichomoniasis and HIV infection.  Diagnostic testing should also be performed in women seeking care for vaginal discharge.

Screening might be considered for persons receiving care in high-prevalence settings (e.g., STD clinics and correctional facilities) and for asymptomatic persons at high risk for infection (e.g., persons with multiple sex partners, exchanging sex for payment, illicit drug use, or a history of STD).

However, data are lacking on whether screening and treatment for asymptomatic trichomoniasis in high prevalence settings or persons at high risk can reduce any adverse health events and health disparities or reduce community burden of infection. (8)  Rectal and oral testing for T.vaginalis is not recommended. (8)

Testing Methods

MICROSCOPIC EVALUATION

Microscopic evaluation of wet mount preparations is the most common method for the diagnosis of T. vaginalis genital infections due to the convenience of the procedure and its relatively low cost. Unfortunately, the sensitivity of the wet mount procedure is low (51-65%) for vaginal specimens (Table 1) and lower still in specimens from men (urethral specimens, urine sediments, and semen. (25) Evaluation of wet mount preps must be done promptly after collection because the already low sensitivity of the procedure declines by to 20% within one hour after collection. (26, 27) While T. vaginalis may be an incidental finding in a Pap test, microscopic examination of conventional or liquid-based Pap specimens should not be used as the primary means for detecting T. vaginalis because false positive and false negative results can occur. (8)

CULTURE

Culture was considered the gold standard method for diagnosing T. vaginalis infection before molecular detection methods became available. Culture has a sensitivity of 75%–96% and a specificity of up to 100%. (25)  In women, vaginal secretions are the preferred specimen type for culture, as urine culture is less sensitive. (25, 28, 29) In men, culture specimens require a urethral swab, urine sediment, and/or semen. To improve yield, multiple specimens from men can be used to inoculate a single culture.

NUCLEIC ACID AMPLIFICATION TESTING (NAAT)

Nucleic acid amplification testing is rapidly replacing culture as the gold-standard for T. vaginalis testing. In the 2015 STD treatment guidelines (8), the CDC recommends the use of highly sensitive NAAT testing for the detection of T. vaginalis. Among women, NAAT detects three to five times more T. vaginalis infections than wet-mount microscopy. (30, 31) When NAAT testing on specimens is not feasible, a testing algorithm (e.g., wet mount first, followed by NAAT if negative) can improve diagnostic sensitivity in persons with an initial negative result by wet mount. (25)

Table 1. Sensitivity of diagnostic methods for detecting
Trichomonas vaginalis in vaginal specimens.

Test Method

Sensitivity

Time to Result

Wet Mount 51-65% <1 hour
Culture 75-96% 1-4 days

Nucleic Acids

95-100%

2-3 days

Trichomonas vaginalis testing at Warde

Warde Medical Laboratory, uses the highly sensitive and specific APTIMA Trichomonas vaginalis Assay for the detection of T. vaginalis ribosomal RNA in clinician-collected endocervical swabs, clinician- collected vaginal swabs, female first-void urine specimens, and specimens in PreservCyt Solution.

Specimens can be collected from symptomatic and asymptomatic patients.  We have also validated the use of male first-void urine specimens and male urethral specimens with this test.  The overall sensitivity of the assay is 95.2% and the specificity is 98.0%.  The analytical sensitivity of the APTIMA procedure is 0.1 organism/mL.

Clinical testing is performed Monday - Friday and the time to result is 1-3 days.  More information about specimen stability, test codes, and LOINC Codes can be found in the Test Catalog on the Warde Medical Laboratory website (wardelab.com).


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