Managing Trichomonas vaginalis infections

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Prevalent and nonreportable, trichomonas infection, when left untreated, can cause complications in women, men, and infants, and co-infection with other STIs increases concerns



CASE Woman with malodorous vaginal discharge

A 26-year-old nulligravid woman with 2 current sexual partners requests evaluation because she has a yellow-green frothy vaginal discharge that is slightly malodorous. One of her sexual partners has noted a similar discharge from his urethra. On physical examination, the clinician notes that the patient’s discharge emanates from the vaginal mucosa, and the exocervix has multiple punctate hemorrhages. Considerations in this case include:

  • What is the most likely diagnosis?
  • How should this patient be evaluated and treated?
  • Should the patient’s sexual partners be treated?

This clinical scenario is most consistent with a trichomonas infection, although other conditions, including bacterial vaginosis, gonorrhea, and chlamydia infection, must be considered in the differential diagnosis.

In this article, we examine the microbiology, epidemiology, clinical manifestations, and diagnosis and treatment of this common sexually transmitted infection (STI).

The causative microbe

Trichomonas vaginalis is a free-living flagellated protozoan that accounts for almost half of all nonviral STIs globally. It has a predilection for the mucosal epithelium of the genitourinary tract, including the vagina and urethra. Humans are the only known host for T vaginalis. The infection is transmitted through sexual intercourse, and the organism reproduces through binary fission in the lower genital tract of women and in the urethra and prostate of men.

This anaerobic trophozoite has 4 flagella anteriorly and 1 flagellum that projects posteriorly, with an undulating membrane that gives its characteristic motile appearance on saline microscopy.1

T vaginalis infection causes major mechanical stress on epithelial cells, which results in disruption of the plasma cell membrane and, ultimately, cell death. The necrotic cell fragments are then phagocytosed by trichomonads, thus accelerating the infection.2

Groups at risk

Trichomonal infections are not reportable to public health authorities, which makes assessing the true prevalence of infection difficult.

The World Health Organization estimated the incidence of infection to be more than 156 million cases globally in 2016, with a prevalence of 110.4 million people at any one time.3

The 2013-2014 National Health and Nutrition Examination Survey tested 4,057 men and women aged 18 to 59 years for T vaginalis and found a prevalence of 0.5% among men and 1.8% among women.4 The prevalence increased with age. There was a disproportionate burden of trichomonas infections in the non-Hispanic black population, with 4.2% of black men and 8.9% of black women affected.4

Targeted screening of urogenital samples for T vaginalis in a population of US women undergoing Chlamydia trachomatis/Neisseria gonorrhoeae screening demonstrated prevalence rates of 8.7%, 6.7%, and 1.7% for T vaginalis, C trachomatis, and N gonorrhoeae, respectively.5

Differences in prevalence estimates may be due to differences in the varying sensitivity of each testing modality and patient populations. In one study, nucleic acid amplification testing (NAAT) for T vaginalis detected rates as high as 11.3% in women and 6.1% in men undergoing evaluations at STI clinics.6

Continue to: Clinical manifestations of infection...


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