Sexually transmitted infections (STI) are caused by several microorganisms such as viruses, bacteria, and parasites that are transmitted primarily by vaginal, oral, or anal sexual contact.1 According to the Centers for Disease Control and Prevention (CDC) of the United States, the annual impact of STIs in 2018 on the North American healthcare system was nearly 16 billion in direct medical costs.2 The World Health Organization (WHO) estimated 374 million new global cases as one of the most common curable STIs among individuals from 15 to 49 years-old only in 2020. Of these, infection by Trichomonas vaginalis is the most prevalent curable STI accounting for nearly half of the cases (156 million).3 Despite the existing treatment regimens with antimicrobial drugs, infections by T. vaginalis are frequently a(oligo)symptomatic and diagnosis is not equally available worldwide, being particularly difficult in low resources regions.

T. vaginalis is a typically pyriform and occasionally amoeboid protozoan with primarily anaerobic metabolism that infects the genitourinary tract epithelium gender-independently.4 Due to its characteristic morphology, microscopy methods have been largely employed for diagnostic purposes, especially for scrutinizing status of culture of clinical samples in specific media. Most commonly reported signs and symptoms include dyspareunia and vaginal discharge, that may be diffuse, malodorous, or yellow green, with or without vulvar irritation. Also, in clinical examination cervical hemorrhagic punctate may be observed, which is often referred to as a “strawberry cervix”.5

Due to the occurrence of pelvic inflammatory disease6,7 and evidence that the infection reduces the viability of sperm, men and women may have reproductive consequences as a result of infection.8 Trichomoniasis may also impact the pregnancy course, causing low birth weight, premature rupture of membranes, and preterm delivery.9

Two population-based studies in the United States observed rates of 2.3% among adolescents10 and 3.1% among women with 14 to 49 years old.11 In Brazil, studies show that prevalence range from 2.6% to 20% in different settings,12–15 while the Brazilian Ministry of Health estimates an overall T. vaginalis prevalence of 15%.16

Several factors were already associated with the incidence of T. vaginalis infection such as younger ages, sexual activity, increased number of sexual partners, condom use, having other STIs, social demographic, and low economic conditions.2,3,17,18 Literature has also shown that T. vaginalis infection is associated with changes in the components of the vaginal microbiota, such as in bacterial vaginosis.19–24 Additionally, it was demonstrated that the presence of T. vaginalis infection increases susceptibility to the Human Immunodeficiency Virus (HIV).25

Studies of prevalence and risk factors for T. vaginalis infection are therefore of great importance to the health care system for the adoption of decisions and for the development of new guidelines for routine primary health care. Thus, this study aimed to identify sociodemographic and clinical factors associated with the prevalence of T. vaginalis infection in reproductive-aged women in community-based clinics in southeast Brazil.

For this study, 1477 women were enrolled and provided full data available for analysis. Median age of participants was 33 years old (ranging from 18 to 50); the majority self-defined their ethnicity as white (62.0%, n = 917) and most of the women were married or living in a steady partner (65.2%, n = 964). In relation to educational level, 59.2% (n = 875) had completed high school. Microscopic analysis of vaginal smears obtained upon study enrollment showed that bacterial vaginosis was detected in 29.8% (n = 440) of the study population (Table 1).

The reported prevalence of T. vaginalis was 1.3% (20/1477). Table 2 shows the results comparing population characteristics according to T. vaginalis status provided. Most of positive cases of T. vaginalis were observed among women that self-reported as black or Pardo (65.0%, n = 13), did not complete high school (80.0%, n = 16), presented habits as smoking in 50.0%, (n = 10) or alcohol consumption in 60.0% (n = 12), and had microscopic bacterial vaginosis at the time of enrollment was 35.0% (n = 13).

Sociodemographic characteristics, sexual behavior, and clinical history were calculated by the logistic regression model considering the T. vaginalis infection as the variable response, estimating each variable's effects as independent. While the prevalence of T. vaginalis was neither sociodemographic characteristics nor sexual behavior dependent (p > 0.05), abnormal microbiota was independently associated with the infection (OR = 4.49; 95% CI 1.78‒11.33) (Table 3). Also, in Table 3, race and ethnicity were categorized as white, black/Pardo and other (Asian, native American). Among all racial/ethnic groups combined, black/Pardo was associated with the infection in both models, univariable (OR = 3.21; 95% CI 1.27‒8.10) and multivariable (OR = 2.70; 95% CI 1.03‒7.08). Higher education level showed a protective effect also in the two models, univariable (OR = 0.17; 95% CI 0.06‒0.51) and multivariable (OR = 0.16; 95% CI 0.05‒0.53). In contrast, tobacco smoke was correlated with an increased risk of infection, univariable (OR=4.44; 95% CI 1.83‒10.78) and multivariable (OR = 3.18; 95% CI 1.23‒8.24). As a result of a multivariable analysis of T. vaginalis infection risk factors, being married or living with a partner proved to be protective compared to singles, divorcees, and widows.

In this study we observed a prevalence of T. vaginalis infection of 1.3% and evidence for a 4-fold increased risk of T. vaginalis infection among women who had abnormal vaginal microbiota. The prevalence found here was similar to observed in other studies in Brazil and worldwide.32–35 Additionally, sociocultural characteristics should also be considered as different across different populations.36

To establish the infection, T. vaginalis must mediate contact with epithelial cells, adhere to, and lyse host epithelial cells, causing tissue damage, generated by a strong infiltration of leukocytes and by high local concentrations of chemokines and pro-inflammatory cytokines.37 Immune responses during infection cause inflammation, which can also contribute to disease establishment, however, T. vaginalis has host immunity evasion mechanisms. Subsequently, the parasite lives associated with the vaginal microbiota, leading to pathogenic ruptures of vaginal bacteria.38 Bacterial vaginosis, a microbiome-disturbance prevalent in reproductive-age women, is characterized by a shift from a Lactobacillus-dominated to a diverse polymicrobial state, with pro-inflammatory features, combined with an immune response driven by individual variability in the host immune system,39 and occurs commonly in concert with trichomoniasis, and its interaction has been suggested.24

The relation between vaginal microbiota and T. vaginalis infection observed in this study corroborates with others.40–42 Although several studies have reported an increased risk of T. vaginalis acquisition among women with bacterial vaginosis, the precise nature of the relationship between the role of T. vaginalis infection in the susceptibility to an unbalance in the vaginal microbial, or even the opposite, a previous imbalance of the microbiota that would favor infection by the protozoan is not well understood.

More longitudinal cohort studies are needed, using accurate detection techniques to demonstrate cause and consequence between vaginal microbiota and T. vaginalis infection. As demonstrated, women experiencing abnormal microbiota during a three-month span appear to have significantly increased risk of acquiring T. vaginalis infection.42

Prevalence of T. vaginalis infection in this study did not differ by economic status, but higher prevalence has been consistently reflected in women who did not complete high school in comparison to having at least completed high school, as demonstrated by Patel et al.,43 and a positive association with infection in participants with lower level of education was demonstrated in previous study.44 The importance of identifying the demographic characteristics of populations at higher risk for acquire STIs may impact the need for effective educational strategies, screening of groups at higher risk and treatment for infected people and sexual partners.

The risk factors for T. vaginalis infection and the prevalence in our study were similar to those observed by Tompkins et al.45 Our studies found risk factors that representing behavioral habits such as smoking were more likely to be infected with T. vaginalis, as compared to non-smokers.

According to our results, the infection rate of T. vaginalis suggests that screening programs to detect this infection could be helpful in establishing prevention strategies in our population. Our study supports an association between abnormal vaginal microbiota and T. vaginalis infection.

GVSP contributed to conceptualization, investigation, methodology, data analysis, writing.

ANB contributed to investigation LFM contributed to investigation NPM contributed to investigation BRAR contributed to investigation.

MDCS contributed to investigation, writing, reviewing and edition MTCD contributed to investigation, writing, reviewing, and edition ART contributed to investigation, writing, reviewing and edition.

MGS contributed to supervision, conceptualization, writing, editing, reviewing, and funding.

CM contributed to supervision, conceptualization, writing, editing, reviewing, and funding.

This study was supported by: developmental funds granted by São Paulo Research Foundation − FAPESP (Grant 2012/01278-0) granted to Dr. Márcia Guimarães da Silva from the Department of Pathology, Botucatu Medical School, UNESP − Univ. Estadual Paulista, Botucatu, São Paulo, Brazil; and by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES (88881.132503/2016-01) granted to Gabriel Vitor da Silva Pinto, Master student in the Post-graduate Program in Pathology, Botucatu Medical School, UNESP − Univ. Estadual Paulista, Botucatu, São Paulo, Brazil. This work was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES) – Finance Code 001.