Chapter 210 Trichomoniasis
Trichomonas vaginalis infection is a common cause of vaginal irritation in women and is the most common nonviral sexually transmitted disease in the world. It is estimated to affect 5 million women in the United States each year alone. One in five women in the United States will have trichomoniasis at some time in her life. Aside from these alarming statistics, there are other reasons for taking trichomonal infections seriously, as follows1,2:
• Trichomoniasis increases transmission and infectivity of human immunodeficiency virus (HIV), such that HIV-seropositive men with concomitant trichomoniasis may have a sixfold higher concentration of HIV RNA in their seminal plasma.
T. vaginalis is a flagellate 15 to 18 micrometers in length. It is shaped like a turnip, with three to four anterior flagella and one posterior flagellum mounted in an undulating membrane. It is transmitted via sexual intercourse. Although women in the past have been thought to be the primary reservoir for Trichomonas and men merely the vector, the medical literature now suggests that men are also reservoirs.3,4
Diagnosis is made from clinical signs and symptoms (see the diagnostic summary), saline wet mount, and culture. Trichomonal cultures (using the Feinberg Trichomonas medium) have recently been advocated to improve diagnostic sensitivity. Although the wet mount is one of the most commonly used and quickest methods to achieve a diagnosis, multiple studies have demonstrated that, compared with culture, the sensitivity of a wet mount ranges from only 45% to 60%.1,2 In men, a reliable culture site has not been established, and cultures from urine and seminal samples have consistently afforded a low yield. Among patients with trichomonal vaginitis, the organism can be cultured from the vagina and paraurethral glands in 98%, from the urethra in 82%, and from the endocervix in 13%. In only 56% to 65% of patients is T. vaginalis seen on a Papanicolaou smear, thus making the smear an unreliable form of diagnosis.1,2 However, recent data suggest that the positive predictive value of this test is acceptable for a diagnosis of trichomoniasis when it is found incidentally on Papanicolaou smear. A meta-analysis found a sensitivity of 57% and a specificity of 97%.5
Rapid point-of-care tests for trichomonal vaginitis are now available; they include the OSOM Trichomonas Rapid Test (Genzyme Diagnostics, Cambridge, Mass), an immunochromatographic capillary-flow dipstick technology, and the Affirm VP III (Becton Dickinson, Franklin Lakes, NJ), a nucleic acid probe test that evaluates for trichomonal vaginitis, Gardnerella vaginalis, and Candida albicans.1 Both of these tests are performed on vaginal secretions and have a sensitivity greater than 83% and a specificity greater than 97%. The results of the OSOM Trichomonas Rapid Test are available in about 10 minutes, and the results of the Affirm VP III are available within 45 minutes. These tests tend to greatly assist physicians in the accurate and timely diagnosis of trichomoniasis.
Sexual transmission is the clear route of Trichomonas infection. Prevalence is highest among women with multiple sex partners and in those with other sexually transmitted infections. Transmission rates from men to women seem to be high, because an 80% to 100% prevalence rate is found in the female partners of infected men.4 In the female, T. vaginalis usually infests the vagina and urethra. However, infection may involve the endocervix, Bartholin glands, Skene glands, or bladder. The vagina appears to be a good reservoir for the organism. Under stimulation of estrogen, the vaginal walls are well glycogenated—essential for T. vaginalis to thrive. Prepubescent and postmenopausal women seldom have symptomatic trichomonal infections.
In addition to estrogen, an elevated pH increases susceptibility to Trichomonas. The normal adult vagina maintains a pH of 3.5 to 4.5 owing to the metabolism of free glucose into lactic acid by vaginal Lactobacillus acidophilus. A decrease in the number of lactobacilli raises pH. Trichomonas organisms grow optimally at a vaginal pH of 5.5 to 5.8. Other conditions that increase vaginal pH are as follows: