Literature review > Issue 7 > Review on Crucitti et al. 

Once upon a time, testing for Trichomonas vaginalis was simple. Most clinicians did not bother, unless they had a woman with symptomatic vaginitis. Trichomoniasis was regarded as a minor venereal disease associated with minimal morbidity. A simple saline wet mount was adequate for diagnosis. In many clinical settings, this remains the standard of care.

This approach is no longer acceptable. Urogenital trichomoniasis causes major morbidity as the most common curable STI. Trichomoniasis has also been shown to increase the risk for HIV infection, and adverse pregnancy outcomes. Numerous studies have documented that the saline wet mount has low sensitivity compared to culture for diagnosis. The newest wrinkle is PCR-based molecular diagnosis. How does this approach compare to culture and what is the best PCR approach? Should PCR-based diagnosis be recommended instead of wet mount and culture methods?

Crucitti and her associates evaluated the test performance of five published PCR primer sets and culture for detection of T. vaginalis in self-collected vaginal swab specimens from sex workers attending a special clinic. Four hundred twenty-five consecutive women, with or without genital complaints, who attended a sex worker clinic in Abidjan, Côte d'Ivoire, as part of a study on the validation of clinical algorithms were tested, providing an adequate sample size. The authors reasonably conclude that the performance of different primer sets was different from what has been described in the literature. There were also important performance differences between the primer sets, which may be explained by T. vaginalis strain variability, specimen type, probe design, and choice of gold standard.

Increased testing for T. vaginalis represents a critical component for effective diagnosis and control of this important pathogen. Given the rapidity, low cost and high specificity of the wet mount, it is difficult for this clinician to recommend abandoning the saline-mixed wet mount as a diagnostic test in all settings. Thus, it was interesting that the diagnostic algorithms evaluated in this study did not include wet mount evaluation and did not consider the patients' clinical presentation. Most experienced clinicians would favor selecting appropriate diagnostic tests based on an individual patient's risk profile, symptoms, and physical findings. The laboratory-only approach considered in this study might prove reasonable in a population with a 20% prevalence of infection. In other settings, clinical acumen may prove a valuable component in developing optimal diagnostic algorithms.

It was interesting to note the number of culture-positive patients who were negative in each PCR-based diagnostic test, including three culture-positive patients who were negative by all 5 PCR tests. Thus, culture may still have a role in diagnosis of trichomoniasis. Other advantages of culture are that some PCR-positive, culture-negative patients may harbor dead or non-viable parasites. We have observed this situation following successful therapy in some patients. Culture also offers the possibility of testing organisms for antimicrobial resistance in patients who do not respond to therapy. Culture methods are less demanding technically than PCR-based diagnostics and are less sensitive to cross-contamination from other specimens or from laboratory sources.

In summary, this article highlights several issues in diagnostic testing for T. vaginalis, including:
-- To what extent should clinical findings or wet mount findings be included in diagnostic algorithms?
-- Can culture be omitted from routine diagnostic testing in high-risk populations?
-- Which PCR-based diagnostic test should be recommended?
-- Do various PCR-based tests perform differently on T. vaginalis isolates from different populations or different geographic areas?

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