Infection with Trichomonas vaginalis increases the risk of becoming infected with HIV

Infection with Trichomonas vaginalis significantly increases a woman’s risk of becoming infected with HIV, according to a study published in the March 1^st edition of The Journal of Infectious Diseases (now online).

It is now well established that several sexually transmitted infections increase the risk of transmission and acquisition of HIV. Although there are 173 million cases of Trichomonas vaginalis per year worldwide, there are few robust data regarding the association of the infection with the risk of HIV acquisition.

A team of investigators from the University of Washington in the United States and Mombasa in Kenya hypothesised that infection with Trichomonas vaginalis increased the risk of HIV acquisition in women and therefore conducted an eleven-year prospective study involving sex workers in Mombasa.

The study ran between 1993 and 2004 and involved 1,335 female sex workers who were HIV-negative at baseline. At monthly intervals, the women provided information about their general medical, gynaecological and sexual health. The women also had physical examinations and were screened for HIV and a variety of sexually transmitted infections, including Trichomonas vaginalis.

The association between Trichomonas vaginalis and HIV acquisition was tested using both univariate and multivariate analysis. The multivariate model controlled for education, alcohol use, workplace (bar versus night-club), vaginal washing practices, genital tract infections other than Trichomonas vaginalis, type of contraceptive used, age, number of sex partners per week, frequency of sex per week, and condom use (100% versus under 100%).

A total of 3,422 person-years of follow-up were available for the investigators’ analysis. There were a total of 806 incident infections with Trichomonas vaginalis (23.6 per 100 person years), and 265 women became infected with HIV (7.7/100 person years).

In univariate analysis, infection with Trichomonas vaginalis was associated with a significantly increased risk of becoming infected with HIV (hazard ratio, 1.60, p = 0.01). This association remained statistically significant after adjustment for sexual risk behaviours, sexually transmitted infections, and the other potential confounding factors noted above (adjusted hazard ratio, 1.52; p = 0.03).

The investigators then turned their attention to the factors associated with Trichomonas vaginalis infection. They found that it was significantly related to shorter duration of prostitution (p < 0.001), under eight years of education (p < 0.001) and concurrent cervicitis (p < 0.001) and bacterial vaginosis (p < 0.001).

Unsurprisingly, 100% condom use was associated with a lower risk of Trichomonas vaginalis, as was the use of progesterone-only contraceptives.

“In the present prospective study, infection with Trichomonas vaginalis was associated with a significantly increased risk of HIV-1 acquisition”, write the investigators.

They suggest several possible reasons why infection with Trichomonas vaginalis increases the risk of HIV acquisition:

• Trichomonas vaginalis leads to inflammation, resulting in cells vulnerable to HIV infection being present in the vaginal and cervical mucosa.
• Trichomonas vaginalis could cause mucosal haemorrhage, damaging natural defences against infection.
• Trichomonas vaginalis undermines a process that can prevent HIV’s attachment to cells.
• Trichomonas vaginalis increases the risk of HIV by increasing susceptibility to vaginal infections or the persistence of abnormal vaginal flora.

The investigators believe that their findings have important implications for HIV prevention. It is thought that 6% of HIV-positive women in the US acquired the infection because of Trichomonas vaginalis, and there is a high incidence of Trichomonas vaginalis in Africa.The investigators therefore conclude, “interventions to prevent and treat trichomoniasis and to improve vaginal health in general could provide important female-controlled methods for reducing the risk of HIV-1 transmission to women.”