Grand Rounds: Could better trichomoniasis screening curb more serious STIs?

August 1, 2005

Because Tv infection is so widespread, increases with age, and—according to important new evidence—raises the risk of both acquiring and shedding HIV, accurately diagnosing this sexually transmitted infection may be an important strategy in fighting the HIV epidemic.

There's new urgency about better detecting and treating trichomoniasis, a sexually transmitted infection (STI) common among sexually active women. Although estimated to be the most prevalent nonviral STI in the world, trichomoniasis has been dismissed as a nuisance infection in the past because it produces only minor symptoms like vaginal discharge and itching.1 But that mindset is changing, prompted by studies over the past few decades that suggest a link between trichomoniasis and serious adverse outcomes like HIV infection. And yet trichomoniasis is still not a reportable disease, nor is it tracked, because most of the infections are detected by in-office tests. Moreover, unlike Chlamydia trachomatis, there are no guidelines for who, or how, to test for it.

New detection methods have highlighted three important new findings: (1) many infections are asymptomatic; (2) unlike other STIs, risk of infection does not decline at age 25; and (3) trichomoniasis may contribute to acquiring and clearing more serious STIs, like HPV and HIV. Our goal is to review trichomoniasis with an emphasis on improving its detection and treatment.

A pear-shaped pathogen A pear-shaped parasitic protozoa, Trichomonas vaginalis (Tv) has four anterior flagella that give the trichomonad its characteristic jerky, swaying motion in wet mount, as well as the undulating membrane, which incorporates the 5th flagellum and is a source of propulsion. The posterior axostile doesn't move, but is thought to anchor the parasite to its host's epithelium. The free-swimming oval parasite looks something like an amoeba when it attaches to the vaginal epithelial cells.

Just how pervasive is this STI? More common than C trachomatis and N gonorrhea, Tv is estimated to account for more than 180 million cases worldwide and roughly 7.4 million in the United States.1,4 There are a variety of reasons why it's difficult to pinpoint its true prevalence: (1) A representative sample of the population has not been tested. Because there are no screening guidelines, who gets tested depends upon the provider and local practice and usually includes only symptomatic women.; (2) There are no reporting requirements for Tv as there are for C trachomatis; (3) Laboratory estimates do not exist because the most common test for Tv is a wet mount, which is an in-office procedure; (4) Finally, the wet mount has a low sensitivity to detect Tv compared to the gold standard (culture). Therefore, the reported prevalence of Tv infections depends on the population studied and the detection method used. First, let's review methods for detecting Tv.