Literature review > Issue 9 > Review on Adu-Sarkodie  et al. 

Increased diagnosis and appropriate clinical management of Trichomonas vaginalis (TV) has been impeded by the wide availability of an accurate, inexpensive, rapid assay that does not rely on the presence of microscopy or other elaborate equipment or laboratory infrastructure. In this paper Adu-Sarkodie and colleagues describe the performance of a latex agglutination test in terms of its suitability for use in resource-poor settings where prevalence of TV (and of HIV-1) tends to be highest.

TV infection usually is detected by identifying motile trophozoites using light microscopy on saline wet mounts of vaginal fluid or spun sediments from male urine specimens. Immunoflourescent and enzyme-linked immunoassays are available, but not widely used. Sensitive DNA amplification techniques such as PCR assays [1] also are not used much beyond research settings due to expense. The gold standard of a TV culture including the 'pouch' culture kit [2] can accurately [3] identify TV but requires incubation, electricity, and up to five daily technician reads. Thus, assessing a point-of-care TV assay whose operating characteristics are germane to the developing world is timely.

In this study, pregnant women (n = 3,807) attending antenatal clinics in Kumasi, Ghana were tested for T. vaginalis infection by a latex agglutination test (Kalon Biologicals, Surrey, UK). All women positive for TV by latex agglutination (n = 206), and the next two women testing negative (n = 412), were tested by wet mount (microscopy at 100X) and culture (InPouch, Biomed Diagnostics, San Jose, CA). Of these 618 women, 55.5% were symptomatic for vaginitis.

The performance of the assays was determined using an expanded gold standard based on the wet mount and culture results. Women were considered to have TV when either the wet mount or culture were positive, and were considered negative for TV when both wet mount and culture were negative. All tests were read independently by different technicians who were blinded to the results of the other tests.

Thirty-five of the 206 latex agglutination positive women were negative by both wet mount and culture. Four hundred ten of the 412 latex agglutination negative women were negative for both wet mount and culture; one woman was positive by wet mount only and one woman was positive by culture only. The kappa value was 0.93 (95% CI 0.91-0.94) for agreement between latex agglutination and culture and 0.88 (95% CI 0.86-0.90) for agreement between latex agglutination and wet prep. One downside was that 6% of samples (n = 35) were latex positive but negative by the other two assays, though the authors were unable to use other diagnostics such as nucleic acid amplification tests to determine whether these were latex agglutination results were false positives.

The authors concluded that the sensitivity of the latex agglutination test compared favorably with culture and was higher than that of the wet mount test. Because the test is rapid (2 minutes), simple to perform (requiring no equipment or incubation), relatively inexpensive (£1), and allows for same-day treatment, more widespread use may be warranted to improve detection and control of TV in resource-constrained settings.

The need for a cheap point-of-care TV test is also underscored by the fact that most men and up to 80 percent of women with TV are asymptomatic. [4] Symptoms that do occur in women may be non-specific, and most female patients will not present with a characteristic frothy green vaginal discharge [5]. Given this, selective screening factors have been limited to date, though recently a targeted screening approach has been developed using three predictors among female STD clinic attendees who were wet-mount negative [6]. A stat assay result might be used to improve the performance of vaginal discharge syndromic management, which as the authors point out, is inadequate at present.

Attention to the control of TV has increased - albeit slowly - as concern about the potential increased risk of HIV acquisition and other adverse impact for both sexes [7] in the presence of TV accumulates [8-11]. The association between TV and HIV-1 is weaker than that noted for candidiasis and bacterial vaginosis (BV); four prospective studies showed no adjusted association with HIV-1 acquisition [12-15}, and one showed some elevation [16]: RR _a 1.7 (1.1-2.8). Thus, population-based screening for TV in asymptomatic women may not soon be instituted on grounds of HIV risk reduction alone, except in those regions with high TV prevalence and epidemic HIV incidence. In these settings, such as in Africa where this study took place, even a moderately elevated individual relative risk can have a substantial population attributable risk [17]. Biological mechanisms for a TV-HIV association are plausible and may occur either through direct mechanisms (increased CD4+ white blood cells and macrophages, mucosal integrity breaks, elevated pH) or in relation to changes in vaginal ecology associated with BV [18,19].

With the exception of having a convenient and accurate test, increased screening for TV at least among targeted higher-risk subgroups may be warranted based on satisfying the assumptions of population-screening [20]. First, the condition is serious (TV's possible association with BV and HIV-1 acquisition, as well as preterm delivery, premature rupture of membranes, low birth weight [21], and urethritis in men). Second, there is a long presymptomatic stage (duration of carriage may be as long as four years on women). Third, treatment is readily available and effective (a Cochrane review has found 5-nitroimidazoles drugs to be effective in achieving parasitological cure in short term follow-up [22]; treatment failure is possible [23], but appears to be relatively infrequent; metronidazole resistance occurs² [24] but may be manageable by administering higher, more prolonged doses of oral metronidazole sometimes augmented with intravaginal applications [25], or use of tinidazole [26,27]).

In this paper a reasonable case is made that the latex agglutination test may be one such inexpensive, easily used rapid TV test that would make more widespread screening for TV possible, at least in high-prevalence resource-poor settings.

References:

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