Abstract
We describe the use of a new molecular assay for Trichomonas vaginalis (TV), the Gen-Probe Aptima TV (ATV) in female attendees at community clinics, a genitourinary (GU) medicine clinic and a prison GU medicine service. Positivity rates at community clinics and GU medicine were 0/382 (0%) and 3/358 (0.8%, 95% confidence interval [CI] 0–1.7%), respectively. Positivity was significantly higher, 29/269 (10.8%, 95% CI 7.1–14.5%), odds ratio (OR) 14.3 (4.11 < OR < 59.55), in those tested at the prison. A questionnaire survey of English GU medicine clinics and data from the UK Health Protection Agency (HPA) for England both demonstrated the large variation in case rates by region and testing methods employed. Higher rates were seen in women, in prison GU medicine services and in London GU medicine clinics. The ATV assay is now CE-marked (Conformité Européenne) and so a larger prospective study of its potential application is warranted.
Keywords
INTRODUCTION
Trichomonas vaginalis (TV) infection is the most prevalent non-viral sexually transmitted infection (STI) globally, and is associated both with reproductive morbidity 1 and with an increased risk of HIV acquisition. 2 Up to 74% of women infected with TV are asymptomatic. 3
Routine methods for diagnosing TV such as wet-film microscopy, acridine orange microscopy and culture of high vaginal swab samples suffer from poor sensitivity and thus underestimate true case rates. Nucleic acid amplification tests (NAATs) with improved sensitivity are now available. 4 One of these tests, the Gen-Probe Aptima TV assay (ATV; Gen-Probe Inc, San Diego, CA, USA) uses transcription mediated amplification and has demonstrated high detection rates with both urine and genital swab samples. 5–7 Our existing regional network care pathway 8 for STIs is based on a ‘dual testing’ assay for Neisseria gonorrhoeae (GC) and Chlamydia trachomatis (CT) by the Gen-Probe Aptima Combo 2 assay, supplemented in genitourinary (GU) medicine clinics by a variety of non-NAAT TV tests (wet film, acridine orange and culture), with not all clinics screening for TV in every patient.
A female prison service within the network reported an unusually high TV positivity rate of 8% (using acridine orange), 9 which is consistent with previous similar work from the USA. 10 Therefore, an opportunity to use ATV (prior to CE-marking [Conformité Européenne]) prompted a prospective comparison of female ATV positivity in three clinical settings – GU medicine, prison and community. Data on male and female TV diagnoses from GU medicine clinics in England were also collected by both a questionnaire survey and from KC60/GUMCAD (GU medicine clinical activity data-set) returns to the UK Health Protection Agency (HPA). 11
METHODS
The aim of this study was to gain pilot positivity data for the use of ATV in our clinics and to put these data into the context of TV epidemiology in England. UK National Research Ethics Service approval was obtained (reference number: 09/MREC09/14). From June to October 2009, all women attending Macclesfield GU medicine, its satellite prison GU medicine service and the community were offered an ATV test on the residual portion of the Aptima transport medium from any vulvovaginal swabs or first-catch urine samples that had been collected for a routine Aptima Combo 2 CT/GC test. Women less than 16 years of age were excluded as well as those unable to give written informed consent or return for treatment. Samples were considered TV-positive when the ATV results from the Gen-Probe TIGRIS analyser (Gen-Probe Inc, San Diego, CA, USA) running TV analyte-specific reagents exceeded 100,000 relative light units. Clinical management and contact tracing were offered to all women with a positive test. Descriptive data and results of routine investigations were gathered from the GU medicine and prison health records for women with a TV-positive result.
The questionnaire asked each GU medicine clinic in England for total female and male attendances, total female and male TV diagnoses and the types of TV test in current use. It also asked about any prison satellite GU medicine clinics provided and data on total prison male and female attendances and total prison male and female TV diagnoses. TV surveillance data by English region were obtained from the HPA for 2008. Statistical analysis was with Epi Info 3.5.1 (CDC, Atlanta, GA, USA).
RESULTS
Prospective study
Female positivity rates by ATV at community clinics and GU medicine were 0/382 (0%) and 3/358 (0.8%, 95% confidence interval [CI] 0–1.7%), respectively. Positivity was significantly higher, 29/269 (10.8%, 95% CI 7.1–14.5%) – odds ratio (OR) 14.3 (4.11 < OR < 59.55) – in those tested at the prison. For the 32 ATV-positive women (Table 1) the mean age was 30.6 (range 19–48) years; 27 were white British/Irish, two Chinese and three were of black African origin; nine (28%) were symptomatic and 3/32 (9.4%) had concomitant CT infection. No woman had concomitant GC infection. This compares to overall CT-positivity rates of 4.6% in the community, 6.3% in GU medicine and 5.3% in the prison and overall GC-positivity rates of 0.09, 0.2 and 0.2%, respectively.
Local study results: recorded clinical characteristics for women who tested TV-positive (all age groups and clinical settings combined)
TV = Trichomonas vaginalis; NAAT = nucleic acid amplification test; STI = sexually transmitted infection; HVS = high vaginal swab
*Only 22 patients had conventional diagnostic tests performed
Of the 32 ATV-positive women, 22 had routine TV tests performed at the same visit, of which 8 (36.4%) were positive. At the GU medicine clinic wet film is the diagnostic method of choice but only symptomatic women are tested. All three of the ATV-positive women from GU medicine had been tested by wet film, only one of whom was positive. In the prison some women were tested at a reception clinic where no routine TV test was available. Others were tested at a clinic for established inmates where TV testing was available for all attendees using acridine orange. Of the 29 ATV-positive women from the prison as a whole, 19 had an acridine orange test of which seven were positive. All women positive by acridine orange or wet film were also positive by ATV at either site.
Case reports to HPA and questionnaire data for GU medicine clinics in England
The HPA provided data on total TV cases reported for women and men, which showed marked regional variation in the numbers of cases reported (Table 2). Response to our GU questionnaire was considered good – accounting for 159 of the 204 GU medicine clinics in England and citing 3229 TV diagnoses compared with the 5610 reported to the HPA for England in 2008. TV-positive female cases (3096) were reported to our questionnaire at an overall rate of 0.67% of attendances. London clinics reported at a rate of a 1.27%, a significantly higher rate (OR 2.65, CI 2.46 < OR < 2.84) than the mean rate for clinics outside London (1682/348,595, 0.49%).
Reported TV diagnoses and testing methods used, by English region
TV = Trichomonas vaginalis; HPA = Health Protection Agency; WF = wet-film microscopy (high vaginal swab), CUL = culture (high vaginal swab); AO = acridine orange microscopy (high vaginal swab); NAAT = nucleic acid amplification test; GU = genitourinary
Only four centres reported on prison data and of these two referred only to very small numbers of attendances. The remaining two centres did however report high TV rates in women (compared with non-prison GU medicine). One of these was in the north west region (31/525 = 5.9%) and the other in the north east region (4/148 = 2.7%).
Male cases (n = 133) were reported to the questionnaire at a rate of 0.03%, which is 22-fold lower than for female cases (P < 0.0001).
Wet film microscopy was by far the most commonly used diagnostic approach; however, detection rates were higher when alternative or additional tests were employed. For example, for attendances in women outside of London, compared with wet film alone (positivity 723/173,813 = 0.42%), detection rates were significantly higher at clinics using (as an alternative or additional test) TV culture (764/129,315 = 0.59%, OR 1.42, CI 1.28 < OR < 1.57) or acridine orange (185/27,894 = 0.66%, OR 1.60, CI 1.35 < OR < 1.89).
The difference between using culture and acridine orange did not reach significance (P = 0.16).
DISCUSSION
The prospective study results presented relate to TV positivity in women in different clinical situations and are not a measure of population prevalence. Using the same assay (ATV) in our three clinical settings yielded marked differences in TV detection rates. The study did not include men so it is unclear whether the disparity between male and female case rates seen in the questionnaire and HPA data reflect lower carriage in men or indicate that more cases are missed due to lack of testing.
The GU medicine clinic questionnaire reported cases for total number of attendances and showed higher rates in women, in prisoners, in London clinics and with use of conventional testing methods other than or in addition to wet-film microscopy. Variation in the range of reported case rates is also reflected in the HPA figures.
Both the choice of populations sampled and the type of test used may need to be considered to address the low detection rates in some settings, which could be seen as a deficiency in the clinical care currently provided for this infection.
Although here ATV served as a research tool, implementation of TV testing by NAAT might be desirable in populations with a high positivity rate. ATV can easily be applied to existing samples obtained for CT/GC, although cost-effectiveness would need to be considered. The assay is now CE-marked and so a larger prospective implementation study is warranted, involving both GU medicine and prison services. It might also be appropriate for NAATs for TV to become a topic of research into cost-effectiveness or a technology appraisal by the National Institute for Health and Clinical Excellence. 12
Footnotes
ACKNOWLEDGEMENTS
We thank Deborah Ritchie (Team Chlamydia Co-ordinator), Dr Joanne Dennis and Dr Sue Walsh of Sexual and Reproductive Health (SRH) and all other nursing and medical staff of both GU medicine and SRH for recruiting patients. We also thank GU medicine clinicians nationally who responded to the questionnaire, the Health Protection Agency UK for GUMCAD data and Steven Lane of the University of Liverpool for statistical advice. Aptima TV assay kits were provided by Gen-Probe who had no role in the conduct of the study or the decision to submit for publication.