A service evaluation of the Gen-Probe APTIMA nucleic acid amplification test for Trichomonas vaginalis: Should it change whom we screen for infection?

Objective: A service evaluation of the new Gen-Probe APTIMA nucleic acid amplification test was performed to determine the prevalence of Trichomonas vaginalis (TV) infection in a UK sexual health clinic and identify risk factors to inform an appropriate TV screening strategy. Method: Unselected patients presenting with a new clinical episode were offered TV testing with Gen Probe transcription-mediated amplification (TV TMA) in addition to routine sexually transmitted infection screening. Asymptomatic females provided a selfcollected vulvovaginal specimen and asymptomatic men a first-void urine sample. Symptomatic patients were examined and a urethral swab taken from men and two posterior vaginal swabs from females; one for culture and one for TV TMA testing. Demographic and clinical data were collected on all patients positive for TV infection and 100 randomly selected TV-negative controls. Results: 3503 patients underwent TV TMA testing during the evaluation period. The prevalence of TV infection was 21/1483, 1.4% (95% CI 0.9% to 2.2%) in men and 72/2020, 3.6% (95% CI 2.8% to 4.5%) in women. The rate of TV positivity was higher in Black Caribbean patients compared with Caucasian patients (men 5.4% vs 0.1%, p<0.001; women 9.0% vs 1.2%, p<0.001). TV TMA detected an additional 16 infections (38%) in symptomatic women compared with culture. Conclusions: While screening all patients with TV TMA will identify more TV infections, the UK prevalence remains low and this approach is unlikely to be cost effective. In addition to testing symptomatic patients, targeted testing of high-risk asymptomatic groups using TV TMA should be considered.