Background and objectives Trichomonas vaginalis is known to be the most common, curable, sexually transmitted infection among sexually active women and may be associated with the acquisition and transmission of HIV. The purpose of this analysis is to determine the prevalence and incidence of T vaginalis and assess risk factors associated with T vaginalis infection in a cohort of women participating in a clinical trial.

Methods We analysed data from women participating in a phase III vaginal diaphragm trial conducted in two communities in Durban, South Africa from 2003 to 2006. A total of 3492 women were screened and 1485 women meeting the respective study eligibility criteria were enrolled. T vaginalis infection was determined at the initial screening visit and at quarterly visits among the enrolled women. Sexual behaviour and sociodemographic data were collected as per the study protocol. Combined data were analysed using STATA V.10.0.

Results At baseline, prevalence of infection was 6.5%. The overall incident rate was estimated to be 8.6/100 women-years. Prevalent T vaginalis infection was associated with having a concurrent chlamydial infection and incident infections were associated with increased number of sex partners.

Conclusions T vaginalis infection was found to be relatively high among this cohort of women. Given the association of this infection with HIV, there is an evident need for T vaginalis screening and treatment in populations at risk for both infections.