Methods for Detection of Trichomonas vaginalis

European Urological Review, 2007:39-41

Trichomonas vaginalis is a protozoan pathogen of the human urogenital tract. The World Health Organization (WHO) estimates that trichomoniasis accounts for more than half of all curable sexually transmitted infections (STIs) worldwide.1 Although accurate surveillance data are lacking, there were an estimated five million new cases of trichomoniasis each year in the US during the late 1990s, exceeding similar figures for gonorrhea and chlamydial infections combined.2 The prevalence of T. vaginalis has been reported to be as high as 26% among female STD clinic patients and 22% among HIV-positive women.3 Recurrent infections are common in women, predominantly due to untreated sexual partners.4 Transmitted primarily by sexual intercourse, T. vaginalis causes vaginitis in women and urethritis in men. While trichomoniasis is well recognised as an aetiological cause of vaginitis, the proportion of non-gonococcal urethritis in men due to T. vaginalis has been estimated to be between 11 and 18%.5 A substantial proportion of infections are asymptomatic, necessitating reliable testing methods. Trichomoniasis is also implicated in various other genito-urinary syndromes, including cervicitis, epididymitis and prostatitis.5 Associations between maternal trichomoniasis and premature rupture of the membranes and pre-term delivery have been reported,6–8 and there is mounting evidence of an association with cervical cancer.9–14

Infection with T. vaginalis can be a marker for high-risk sexual behaviour, and frequently occurs concomitantly with other STIs, including gonorrhea and chlamydia.5 Trichomoniasis is associated with incident herpes simplex virus (HSV)-2 infection15 and with genital HSV-2 shedding in infected women.16 As with other STIs, trichomoniasis in the male or female genital tract is associated with increased sexual transmission of HIV.17–21 Co-infection with T. vaginalis and HIV may increase the infectiousness of both organisms.17,22 As the prevalence of trichomoniasis is so high, a large proportion of HIV infections could be attributable to T. vaginalis infection in populations where both infections are common.3 Diagnosis of trichomoniasis based solely on clinical signs and symptoms is unreliable because the spectrum of infection is broad and other sexually transmitted pathogens can cause similar signs and symptoms.5 Diagnosis is particularly challenging in men, where infections are characterised by fewer organisms than infections in women.23,24 In this report, we review the performance characteristics, advantages and limitations of currently available T. vaginalis detection methods.

Direct Microscopy
In clinical practice, laboratory diagnosis of trichomoniasis has previously relied on microscopic examination of a wet-mount preparation of vaginal discharge or male urine sediment. Because of the characteristic shape and unique tumbling motility of live T. vaginalis in such preparations, wet-mount microscopy is assumed to have perfect specificity. In expert hands, wet-mount microscopy can be 50–70% sensitive in specimens from women, but the technique is much less reliable in specimens from men.5

Diagnosis by wet-mount requires visualisation of viable, motile protozoa; therefore, specimens must be examined immediately. The sensitivity of wet-mount microscopy can be further reduced as a result of delays between specimen collection and examination.25 Despite its limited sensitivity, wet-mount microscopy may be widely used because it is inexpensive and positive results can be obtained quickly, allowing patients to be treated during a single clinic visit. T. vaginalis can also be visualised in fixed vaginal, cervical or urine sediment smears stained using various staining methods, including Gram, Giemsa, Papanicolaou, periodic acid-Schiff, acridine orange, fluorescein and immunoperoxidase. Papanicolaou-stained smears can be used to detect T. vaginalis in asymptomatic women during routine examinations.26–30 Detection using the Papanicolaou test has reported sensitivity of 60% and specificity of 95–97%;30,31 however, confirmation of trichomonads using another method is recommended.

Culture
Culture, using a variety of liquid and semi-solid media, remains the reference standard for diagnosis of trichomoniasis in women.5,32–34 Culture pouches containing modified Diamond’s medium are commercially available and convenient (InPouch TV, Biomed Diagnostics, White City, OR). After inoculation with a vaginal swab specimen or urine sediment, cultures are incubated for three to five days at 37°C in a 5% CO2 atmosphere and examined daily using microscopy for motile trichomonads. Cultures from women with trichomoniasis are usually positive within the first three days. In studies comparing the detection of T. vaginalis using culture and highly sensitive nucleic acid amplification tests, sensitivity estimates for culture range from 69 to 75% with specimens from women.35–37 However, because positive cultures may result from the growth of even a few trichomonads in a clinical specimen, this method is more sensitive than wet-mount microscopy and substantially improves detection of T. vaginalis. Vaginal swab specimens transported in Amies gel transport tubes maintain T. vaginalis viability for up to 24 hours prior to inoculation into culture media.38 Trichomonads from vaginal swab specimens have been shown to remain viable in a small amount of saline for up to 20 minutes prior to culture inoculation.39 A combined approach of microscopy followed by culture if the wet-mount is negative can increase diagnostic sensitivity in women over microscopy alone.40 T. vaginalis culture is less sensitive for detection of trichomoniasis in men.23,41–43 Furthermore, cultures inoculated with specimens from men should be incubated and examined daily for the full five days, since they often do not become positive until after three or more days of incubation.42 Although culture of T. vaginalis in men is preferred over wet-mount microscopy for diagnosis, the optimal specimen for culture is not clear. Studies indicate that sampling multiple urogenital sites substantially increases the detection of T. vaginalis in men.24,44,45 Semen cultures have been shown to be valuable for documentation of infection; infections may be diagnosed by positive semen cultures in the face of concomitant negative cultures from urine, urethral swabs or external genitalia.24,45 However, collection of semen for diagnostic purposes is not feasible in most clinics, and microscopic examination of more than one specimen per subject is time-consuming. A practical approach is to combine a urethral swab specimen with a first-voided urine sediment in a single culture.24

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