Background UK national guidelines recommend screening for Trichomonas vaginalis (TV) in symptomatic women and men with persistent urethritis using culture +/− wet mount microscopy. Screening of asymptomatic patients is not recommended due to the low prevalence of infection and low sensitivity of available tests. TV NAAT has been shown to have high sensitivity (96.7%) and specificity (97.5%) with the potential to increase the detection rate of TV infections.

Objectives To determine an accurate prevalence of TV infection in a UK STI clinic using the TV NAAT and to characterise the risk factors associated with TV infection to inform an appropriate screening strategy.

Method Over a 6-week period, unselected patients presenting to the UK STI clinic with a new clinical episode were offered a TV NAAT test (Gen Probe transcription-mediated amplification) as part of their sexual health screen. A vaginal swab was taken from women, and men provided either a urethral swab or urine sample. Information on demographics and clinical presentation was collected on a paper proforma. All data analysis was performed using SPSS V.19.

Results 3546 patients were seen in the study period of whom 98.8% provided a sample for TV NAAT testing. The prevalence of TV infection was 21/1483, 1.4% (95% CI 0.9% to 2.2%) in male patients and 72/2020, 3.6% (95% CI 2.8% to 4.5%) in female patients. The rate of TV positivity was higher in Black Caribbean patients compared to Caucasian patients in both men (5.4% vs 0.1%, p<0.001) and women (9.0% vs 1.2%, p<0.001). There was no significant difference in TV positivity across the age groups. In comparison to culture, TV NAAT detected an additional 24% of infections in symptomatic women.

Discussion TV NAAT is a more sensitive test. The prevalence of TV in UK STI clinic population is still low compared to USA. Given the higher cost of NAAT, screening of all clinic patients is unlikely to be cost-effective but may be worth considering in high risk subgroups.