INTRODUCTION — Trichomoniasis is a genitourinary infection with the protozoan Trichomonas vaginalis. It is the most common nonviral sexually transmitted infection (STI) worldwide. Females are affected more often than males. Trichomoniasis is one of the three common infectious causes of vaginal complaints among reproductive-aged females, along with bacterial vaginosis (BV) and candida vulvovaginitis, and a cause of non-gonococcal urethritis in males; however, the infection is often asymptomatic.
Related topics on the approach to the evaluation of vulvovaginitis and urethritis are presented separately:
●(See "Urethritis in adult males".)
In this topic, we use the terms "women" or "men" as they are used in the studies presented. However, we encourage the reader to consider the specific counseling and treatment needs of transgender and gender-diverse individuals.
Microbiology and transmission — The organism responsible for trichomoniasis is the flagellated protozoan T. vaginalis, which principally infects the squamous epithelium in the urogenital tract: vagina, urethra, and paraurethral glands . Other less common sites include the cervix, bladder, Bartholin glands, and prostate. Positive tests from oral and rectal sites have also been reported [2-4]. Humans are the only natural host, and it is the most common nonviral sexually transmitted infection (STI) worldwide [1,5,6]. The parasite is a pear- or round-shaped organism with four anterior flagella and an undulating membrane that causes the characteristic motility seen on a diagnostic wet-mount slide of vaginal sections . (See 'Preferred tests' below.)
Trichomoniasis is virtually always sexually transmitted . Although survival on fomites has been reported , transmission by fomites has not been directly proven . Females can acquire the disease from both females and males, while males typically acquire the infection from females and do not usually transmit the infection to other males [11-13]. The incubation period is unknown; however, in vitro studies suggest an incubation period of 4 to 28 days in approximately 50 percent of patients . Coexistence of T. vaginalis and bacterial vaginosis (BV) is common; coinfection rates ranging from 20 to 60 to 80 percent have been reported [15,16].
Prevalence — Globally, the World Health Organization (WHO) estimates that more than 156 million new trichomoniasis infections occurred in 2020 . However, prevalence estimates vary according to the population studied (based on age and behavioral risk factors), community-wide disease prevalence, and method used for diagnosis. Trichomoniasis has been reported in transgender individuals both with and without gender-affirming surgery . Use of nucleic acid amplification tests (NAATs) results in higher prevalence rates compared with wet mount microscopy and vaginal pH testing [19-22]. (See "Vaginitis in adults: Initial evaluation", section on 'Nucleic acid amplification tests (NAATs)'.)
Available prevalence studies use self-reported gender when categorizing populations:
●Prevalence in women – Reported prevalence rates in females vary widely. A meta-analysis of 18 studies including over 37,000 self-reported women from African countries noted prevalence rates ranging from 2 to nearly 30 percent; influencing factors included age group of study and risk status of the population . Studies that used NAATs to detect T. vaginalis in US women reported overall prevalence ranges from 8.7 to 27 percent [24,25]. Prevalence varied by clinical setting (5 to 7 percent in family planning, internal medicine/family practice, and obstetrics and gynecology offices to 16 to 27 percent in prisons and STI clinics).
The age distribution of trichomoniasis infections in women appears to differ from other STIs. In a polymerase chain reaction (PCR) study of cervicovaginal samples obtained during gynecologic examinations, the peak rate of detection for T. vaginalis occurred in women ages 47 to 53 years, compared with 14 to 20 years for Chlamydia trachomatis . In addition, while rates of chlamydia infection rapidly declined after peak detection, T. vaginalis infections had a bimodal distribution with infection peaks occurring in women ages 21 to 22 years and 48 to 51 years.
●Prevalence in men – Studies using NAATs to screen US men at risk for STIs have reported T. vaginalis prevalence rates of 4 to nearly 10 percent [22,25,27]. As with females, prevalence in males has been reported to increase with increasing age [26,28]. When male sexual partners of females with confirmed T. vaginalis infection are studied, T. vaginalis can be identified in up to 70 percent , although carriage in males is often self-limited.
Prevention — The risk of acquiring T. vaginalis infection can be reduced by correct and consistent use of condoms and use of spermicidal agents such as nonoxynol-9 [13,30]. Discussion of contraceptive methods that reduce STI transmission are available separately.
The approach to treating sexual partners of individuals with confirmed trichomonas infection is presented in related content. (See "Trichomoniasis: Treatment", section on 'Sex partners'.)
SCREENING — Routine screening for T. vaginalis infection is not advised for asymptomatic persons without HIV infection who do not have risk factors. However, as approximately 70 percent of individuals with T. vaginalis infection may be asymptomatic  and infection can increase the risk of pelvic inflammatory disease as well as acquisition of HIV and other sexually transmitted infections (STIs), screening of various at-risk populations can been considered. The US Centers for Disease Control and Prevention (CDC) recommend screening for T. vaginalis in all HIV-infected females at their initial visit and annually . In addition, screening is reasonable for any person at increased risk of Trichomonas infection, including those in high-prevalence settings (eg, STI clinics, correction facilities), with new or multiple sex partners, with a history of transactional sex work, or with a history of STIs. Additional discussion related to screening for T. vaginalis is available separately. (See "Screening for sexually transmitted infections", section on 'Assessing risk'.)
By contrast, testing for T. vaginalis is indicated for any sexually active individual with symptoms suggestive of trichomoniasis infection, particularly those with abnormal vaginal or urethral pain or discharge.
●(See 'Clinical features and consequences' below.)
●(See 'Diagnostic evaluation' below.)
CLINICAL FEATURES AND CONSEQUENCES — Trichomonas infection ranges from an acute, severe inflammatory disease to an asymptomatic carrier state.
•Acute infection – Symptoms of infection in females include a purulent, malodorous, thin vaginal discharge associated with burning, pruritus, dysuria, frequency, lower abdominal pain, and/or dyspareunia . However, typical symptoms may occur in only 11 to 17 percent of those with confirmed infection; thus, providers should have a low threshold to test for trichomonas when any vaginal discomfort is present . Symptoms may be worse during menstruation . Postcoital bleeding can occur.
•Chronic infection – Signs and symptoms of chronic infection are milder and may include pruritus and dyspareunia, with scanty vaginal discharge. Rates of asymptomatic infection from 66 to 85 percent have been reported; results vary by test used and population studied [13,31,35]. Asymptomatic carriage can persist for prolonged periods of time (at least three months), although many will ultimately develop symptoms [7,13]. Thus, it is often not possible to ascertain when or from whom the infection was acquired [36,37].
●Physical examination findings – Physical examination often reveals erythema of the vulva and vaginal mucosa. The classically described green-yellow, frothy, malodorous vaginal discharge occurs in 10 to 30 percent of symptomatic women . Punctate hemorrhages may be visible on the vaginal mucosa and/or cervix (ie, strawberry cervix or colpitis macularis) in only a small percent of cases (picture 1) .
●Clinical consequences – Consequences of trichomoniasis vary by population:
•Nonpregnant patients with a vagina – Untreated T. vaginalis infection may result in:
-Urethritis or cystitis .
-Posthysterectomy cuff cellulitis or abscess .
-Pelvic inflammatory disease [41,42].
-Increased risk of HIV acquisition and/or transmission – Trichomoniasis has been associated with increased risk of HIV susceptibility (up to twofold increase for females) [44-46] and transmission to uninfected partners [47-49]. There is some evidence that treatment of trichomoniasis reduces HIV shedding [47,48,50].
-Acquisition of other sexually transmitted infections (STIs) – Trichomoniasis has been associated with increased acquisition of other STIs (including herpes simplex virus 2, chlamydia, gonorrhea, and human papilloma virus [HPV]) [24,51,52].
-Cervical neoplasia – While multiple studies have reported an association between trichomoniasis and cervical neoplasia, some antedated testing for HPV coinfection [53-56]. Subsequent studies have reported an association between infection with T. vaginalis and high-risk HPV subtypes, which suggests an indirect link between T. vaginalis and cervical neoplasia [57,58]. A study of 324 Tanzanian women reported that those T. vaginalis were 6.5 times more likely to have high-risk HPV . Similarly, a study of 536 Brazilian women reported a 2.2-fold increased odds for high-risk HPV in individuals with concurrent trichomonas, a threefold higher odds for low-grade squamous intraepithelial lesions, and 12-fold higher odds for atypical squamous cells cannot exclude high-grade squamous intraepithelial lesion (ASC-H) .
•Pregnant individuals – T. vaginalis infection during pregnancy is associated with adverse obstetric outcomes including premature rupture of the membranes, preterm delivery, and delivery of a low birth weight infant [35,60-64]. In a meta-analysis of 19 studies that evaluated the association between T. vaginalis and perinatal outcomes, trichomoniasis during pregnancy was associated with a 27 percent increased risk of preterm birth (odds ratio [OR] 1.27, 95% CI 1.08-1.50), 87 percent increased risk of prelabor rupture of membranes (OR 1.87, 95% CI 1.53-2.29), and more than double the risk of low birthweight (OR 2.12, 95% CI 1.15-3.91) . Whether treatment in pregnancy affects these risks, positively or negatively, is unclear . (See "Trichomoniasis: Treatment", section on 'Pregnant'.)
Male — Trichomoniasis can cause symptoms of urethritis in males. When present, symptoms consist of a clear or mucopurulent urethral discharge and/or dysuria and are the same as for urethritis from any cause [66,67]. There may also be mild pruritus or a burning sensation in the penis after sexual activity. However, T. vaginalis infection is asymptomatic in over three-quarters of cases and often transient (spontaneous resolution within 10 days) [29,68], although untreated infection can persist for months . (See "Urethritis in adult males", section on 'Clinical manifestations'.)
T. vaginalis has also been associated with prostatitis [70,71], epididymitis, slowed sperm motility and infertility [72,73], and, possibly, prostate cancer [74,75]. (See "Risk factors for prostate cancer", section on 'Trichomonas vaginalis infection'.)
Newborns — Infants born to an infected person may contract infection during delivery. Signs and symptoms in neonates may include fever, respiratory problems, urinary tract infection, nasal discharge, and, in females, vaginal discharge [76-79]. Treatment of asymptomatic infants is not necessary as spontaneous resolution will occur when estrogen levels wane to normal prepubescent levels .
DIAGNOSIS — The diagnosis of T. vaginalis is based on testing (positive nucleic acid amplification test [NAAT], motile trichomonads on wet mount of vaginal secretions, positive culture, or positive rapid antigen or nucleic acid probe test) that confirms T. vaginalis infection . (See 'Preferred tests' below.)
Preferred tests — Preferred diagnostic tests include nucleic acid amplification tests (NAATs, for vaginal or urethral discharge) or testing of vaginal pH and microscopy. Approach is based on test availability and provider training (algorithm 1).
●Explanation and comparison of test types – Comparison of testing methods is reviewed in detail in related content. (See "Vaginitis in adults: Initial evaluation", section on 'Test vaginal discharge'.)
●Treatment of positive test – Treatment of individuals with a positive test result is presented separately. (See "Trichomoniasis: Treatment".)
Nucleic acid amplification tests (all patients) — Nucleic acid amplification tests (NAATs) are preferred for diagnosing T. vaginalis infection in all patients (female and male) because of the high sensitivity and specificity (both approaching 100 percent) compared with microscopy (vaginal discharge) or culture (vaginal or penile secretions) (table 1) [13,19-21,81-83]. Limitations of NAATs, compared with microscopy for female patients, include longer turnaround time and higher cost [19-21]. (See "Vaginitis in adults: Initial evaluation", section on 'Nucleic acid amplification tests (NAATs)'.)
●Male patients – NAAT testing is typically performed on a urethral swab, although positive NAATs of rectal swabs have also been reported . Not all commercial NAAT assays are approved for use in male patients; clinicians should speak with their lab to understand test availability. (See "Urethritis in adult males".)
●Female patients – NAAT may be the primary test or used as a secondary test for female patients with concerning symptoms and/or vaginal discharge but negative microscopy results. (See "Vaginitis in adults: Initial evaluation", section on 'pH and microscopy'.)
pH and microscopy of vaginal discharge — If NAAT is not available, vaginal discharge can be evaluated with pH testing and microscopy. pH and microscopy are convenient, provide results during the office visit, and cost less than laboratory tests but require a trained provider and are less accurate (table 1) [13,20,21]. Compared with NAATs, microscopy has a reported sensitivity of 26 to 68 percent [84,85]. (See "Vaginitis in adults: Initial evaluation", section on 'pH and microscopy'.)
Specific to trichomoniasis, typical findings include:
•The motion is jerky and spinning (movie 1 and movie 2). Organisms remain motile for only 10 to 20 minutes after collection of the sample. The slide should be evaluated soon after obtaining the specimen as sensitivity decreases over time, with up to 20 percent decrease reported one hour after collection [13,87,88].
•Fixation and staining is not useful because T. vaginalis may not have the typical pear-shaped flagellated form; instead, it may resemble polymorphonuclear leukocytes or lose morphologic characteristics during fixation and staining, making the etiologic identification difficult .
●pH and other – Findings with T. vaginalis infection include an elevated vaginal pH (>4.5), although the pH can occasionally be normal in the presence of infection, and an increase in polymorphonuclear leukocytes on wet mount microscopy. However, these additional findings are not diagnostic as they can be found in other vaginal infections (table 2).
pH and microscopy (either wet mount or gram stain) are not applicable for urethral or anal specimens. Saline microscopy of a urethral swab specimen from male patients has low sensitivity and is not recommended. (See "Urethritis in adult males".)
●Culture – Culture is performed if neither NAATs nor microscopy are available. Culture of vaginal secretions on Diamond's medium was the historic gold standard method for diagnosing T. vaginalis infection before the development of molecular detection methods (NAATs); however, this is not as sensitive as NAATs . Compared with NAATs, the sensitivity of culture for trichomonas has been reported between 45 and 93 percent with specificity up to 100 percent [13,20,81,91-94]. Although this test is not widely available and takes up to seven days to obtain a result, culture may be useful in patients with elevated vaginal pH and increased numbers of polymorphonuclear leukocytes but an absence of motile trichomonads and clue cells on wet mount, when microscopy is unavailable or yields ambiguous results, or when NAATs are not available. It is also useful when drug susceptibility testing is needed in cases of persistent infection. The "InPouch" T. vaginalis culture system has high sensitivity (over 80 percent) and is commercially available [95,96].
●Cervical cytology – Trichomonads are sometimes reported as an incidental finding on tests performed for cervical cancer screening.
•Liquid-based cervical cytology – Liquid-based cervical cytology is not a sensitive test for trichomoniasis but specificity is high. Therefore, treating individuals with trichomonads noted on liquid-based cervical cytology is reasonable. In a study that performed both liquid-based cervical cytology and culture for T. vaginalis on 203 consecutive self-reported women, 28 had a liquid-based smear positive for trichomonads, and 44 had positive cultures . Although sensitivity of liquid-based smears for Trichomonas infection was low (61 percent), specificity was high (99 percent). A second study using polymerase chain reaction (PCR) testing of stored samples confirmed T. vaginalis in 50 out of 51 samples called positive by cytology and identified the organism in 2 out of 195 samples that had been read as negative. For this population, cytology had a sensitivity of 96.2 percent and specificity of 99.5 percent .
•Conventional Pap smear – Conventional Pap smear should not be used to diagnose trichomoniasis. Although the sensitivity is similar (51 to 63 percent) to liquid-based tests, false-positive results are common (7 percent) . This makes the positive predictive value poor in a low prevalence population. Asymptomatic individuals with trichomonads identified on a conventional Pap smear should be evaluated by NAAT, wet mount microscopy, or culture (selection is based on availability).
Additional STI testing — Individuals undergoing testing for trichomoniasis are generally offered testing for other sexually transmitted infections (STIs), including gonorrhea, chlamydia, syphilis, and HIV . Testing for STIs is presented separately. (See "Screening for sexually transmitted infections", section on 'Screening recommendations'.)
Female patients — Vaginal discharge is a nonspecific symptom that can be caused by vaginal infections, cervical infections, and, less commonly, atrophy related to hypoestrogenism, and irritation.
●Vaginal infections – The most common infections responsible for vaginal discharge, odor, pruritus, and/or discomfort are bacterial vaginosis (BV), Candida vulvovaginitis, and trichomoniasis; these infections account for over 90 percent of cases . The clinical features that distinguish among these infections are presented in the table (table 2). Detailed discussions of the clinical manifestations and management of BV and vulvovaginal candidiasis are presented separately:
●Cervical infections – The sexually transmitted cervical infections gonorrhea and chlamydia also cause symptomatic vaginal discharge, but less commonly than vaginal infections [101,102]. In two studies of self-reported women presenting with symptomatic vaginal discharge in resource-limited countries, cervical infection with either gonorrhea or chlamydia was present in 5 to 24 percent of patients compared with vaginal infection (ie, BV, vulvovaginal candidiasis, or trichomoniasis), which was present in over 50 percent of patients [101,102]. Organism-specific testing is required to identify the infectious cause(s) of vaginal discharge. Clinical presentations and management of cervical sexually transmitted infections (STIs) are discussed elsewhere:
●Other – Less common causes of vaginal discharge that could be mistaken for trichomoniasis include vaginal atrophy/atrophic vaginitis in hypoestrogenic females, retained foreign body, irritants and allergens (ie, dermatitis), desquamative inflammatory vaginitis, and several rare entities, including some systemic medical disorders. Targeted testing is performed to exclude infection, including T. vaginalis. Once infectious etiologies have been excluded, then the evaluation continues to exclude noninfectious causes. (See "Vaginitis in adults: Initial evaluation", section on 'No diagnosis after initial evaluation'.)
Male patients — Urethritis in males is typically caused by a sexually transmitted pathogen. As with vaginal discharge, urethritis is a nonspecific symptom and testing is performed to identify or exclude infectious organisms, most commonly Neisseria gonorrhoeae, Chlamydia trachomatis, and Mycoplasma genitalium. The evaluation and management of patients with urethritis is presented elsewhere. (See "Urethritis in adult males".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Sexually transmitted infections".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Trichomoniasis (The Basics)")
RESOURCES FOR PATIENTS AND CLINICIANS — The following resources are available to patients and clinicians at no cost.
●World Health Organization – Guidelines for the management of symptomatic sexually transmitted infections
●National Health Service (UK) – Trichomoniasis
●US Centers for Disease Control and Prevention – STI Treatment Guidelines
SUMMARY AND RECOMMENDATIONS
●Microbiology – Trichomoniasis is caused by the protozoa Trichomonas vaginalis. The organism principally infects the squamous epithelium in the urogenital tract: vagina, urethra, and paraurethral glands. Less common sites include the cervix, bladder, Bartholin glands, and prostate. Humans are the only natural host and it is virtually always sexually transmitted. Coinfection with other sexually transmitted infections (STIs) and bacterial vaginosis (BV) is common. (See 'Microbiology and transmission' above.)
●Screening – Routine screening for T. vaginalis infection is not advised for asymptomatic persons without HIV infection who do not have risk factors. However, as infection with T. vaginalis is often asymptomatic and has clinical consequences, screening can be considered for high-risk populations but is not standardized. (See 'Screening' above.)
By contrast, testing for T. vaginalis is indicated for any sexually active individual with symptoms suggestive of trichomonas infection, particularly those with abnormal vaginal or urethral pain or discharge. However, typical symptoms may occur in only 11 to 17 percent of those with confirmed infection; thus, providers should have a low threshold to test for trichomonas when any vaginal discomfort is present. (See 'Clinical features and consequences' above.)
●Clinical features and sequelae – Trichomonas infection ranges from an acute, severe inflammatory disease to an asymptomatic carrier state. (See 'Clinical features and consequences' above.)
•Females – Signs and symptoms include a purulent, malodorous, thin vaginal discharge with associated burning, pruritus, dysuria, frequency, and/or dyspareunia. T. vaginalis has been associated with a range of adverse reproductive health outcomes, including posthysterectomy cuff cellulitis or abscess, pelvic inflammatory disease, infertility, and preterm birth. It may also increase susceptibility to HIV-1 infection and other STIs. (See 'Female' above.)
•Males – Symptoms, when present, are the same as for urethritis from any cause and consist of a clear or mucopurulent urethral discharge and/or dysuria. However, T. vaginalis infection is asymptomatic in over three-quarters of cases, is often transient (spontaneous resolution within 10 days), yet can also persist for months. As a result, it is often not possible to ascertain when or from whom the infection was acquired. (See 'Male' above.)
•Newborns – Infants born to an infected person may contract infection during delivery. Signs and symptoms in neonates may include fever, respiratory problems, urinary tract infection, nasal discharge, and, in females, vaginal discharge [76-79]. Treatment of asymptomatic infants is not necessary. (See 'Newborns' above.)
●Diagnosis – Preferred tests for T. vaginalis infection include nucleic acid amplification tests (NAATs, performed on vaginal or penile discharge) or microscopic evaluation of vaginal discharge that confirms motile trichomonads (picture 2). Culture and liquid-based cervical cytology can diagnose trichomonas but are not preferred tests because of lower sensitivity compared with NAATs. (See 'Diagnostic evaluation' above.)
●Differential diagnosis – Vaginal discharge is a nonspecific symptom that can be caused by vaginal infections, cervical infections, and, less commonly, atrophy related to hypoestrogenism, and irritation. Urethritis in males is typically caused by a sexually transmitted pathogen. (See 'Differential diagnosis' above.)
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