Trichomonas Vaginalis: Identify, Investigate, and Refer

Dr Rebecca Mawson Discusses the Role of Primary Care in the Investigation and Diagnosis of This Under-recognised Sexually Transmitted Infection 

Trichomonas vaginalis is a flagellated protozoan parasite that is almost exclusively spread by sexual contact.^1,2 Globally, trichomoniasis is the most prevalent nonviral sexually transmitted infection (STI), with an estimated 276.4 million cases per year,² so it is particularly relevant for those practitioners working with new migrant populations. In the UK, diagnoses of trichomoniasis are less common, with over 6000 cases reported in English genito-urinary medicine clinics in 2011;³ in contrast, over 150,000 cases of chlamydia were diagnosed between 2020 and 2021.⁴ The organism is found in the vagina, urethra, and paraurethral glands in women,¹ and in the urethra, head of the penis, and prostate gland in men.^1,5

According to national STI surveillance, over 90% of cases of T. vaginalis infection occur in women.^3,6 This disparity may be a result of men clearing the organism more quickly;^2,6,7 alternatively, it may reflect the fact that women are more routinely tested for T. vaginalis at sexual health clinics.^3,7 The infection is more prevalent in women of Black Caribbean ethnicity or other Black ethnicities,^3,6 a difference that may be explained by genetic variations in the vaginal microbiome, which is linked to susceptibility to prolonged genital infections.⁸ It has also been suggested that this difference is influenced by a combination of social, cultural, and socioeconomic factors.^3,4,6

This article explores the recent British Association for Sexual Health and HIV (BASHH) guideline on T. vaginalis infection¹ in the context of primary care, and discusses barriers to its widespread use. The guideline, which covers the management of people aged 16 years or older, is tailored to sexual health settings—indeed, there were no primary care authors on the paper—and focuses on cisgender individuals, as there are insufficient good-quality data about T. vaginalis infection in the transgender community.¹

Clinical Features

Because there is currently no routine screening programme for T. vaginalis,² the infection is usually diagnosed in symptomatic patients. However, the signs and symptoms of T. vaginalis infection, as outlined in Table 1,¹ can vary significantly between patients.

Table 1: Key Clinical Features of Trichomonas Vaginalis Infection¹

One of the challenges of diagnosing trichomoniasis is that most of the signs and symptoms are nonspecific,^2,5 and the pathognomonic signs are rare in people infected with the organism.² Interestingly, the classic signs taught in medical school objective structured clinical examinations have a relatively low incidence: frothy yellow discharge is present in only 10–30% of cases, and vulval erythema and punctate haemorrhagic spots in the cervix (‘strawberry cervix’) are only visible to the naked eye in 2% of women.¹

Investigations in Primary Care

Although there have been advances in techniques for identifying T. vaginalis that mean that the infection can be diagnosed with more accuracy and without the need for microscopy, it is still rarely diagnosed in primary care. In sexual health clinics, T. vaginalis has traditionally been diagnosed by a trained clinician identifying the protozoan under a microscope.^1,2 Women with vaginal discharge have a swab taken from the posterior fornix of the vagina, which is then examined under a microscope¹—using this method, other conditions like bacterial vaginosis^9–11 and gonorrhoea¹² can also be visualised.

Taking Samples for Testing

Women

The BASHH guideline suggests that, in the absence of microscopy and where resources allow, nucleic acid amplification tests (NAATs) can be used to test for the presence of T. vaginalis in women.¹ This is the same technique used for the detection of chlamydia and gonorrhoea in primary care.^12,13 As with testing for chlamydia and gonorrhoea,^12,13 patient-administered swabs are likely to give the same results as clinician-administered swabs.¹ Urine NAATs also have acceptable sensitivity for women with symptoms, and are permissible according to the guideline.¹

Men

BASHH recommends that men have an NAAT swab taken from the meatus of the penis; this can be taken by the clinician or the patient.¹ Urethral swabs taken by a clinician are also acceptable, but at present urine specimens do not produce results good enough for their use to be recommended in men.¹

Making a Diagnosis

NAATs for T. Vaginalis

Most localities provide NAATs for chlamydia and gonorrhoea in primary care, as they are the gold-standard diagnostic tests.¹⁴ Unfortunately, NAATs for T. vaginalis are not readily available in primary care; because the infection has a low prevalence, triple testing for chlamydia, gonorrhoea, and T. vaginalis is not considered cost effective.¹⁵ This is the main barrier to testing or screening for T. vaginalis in general practice.

Charcoal High-vaginal Swab Samples

In primary care, charcoal swabs can be used to detect causes of vaginal discharge such as bacterial vaginosis;¹⁶ in theory, these swabs would also be able to detect T. vaginalis,^16,17 but unfortunately the live protozoan needs to be transferred to the lab promptly—this is not easily achievable in primary care.¹⁸

Point-of-care Testing

Point-of-care testing (POCT) may be the answer to the T. vaginalis conundrum, as POCT of vaginal discharge using relatively new rapid tests can allow clinicians to make a diagnosis in primary care.¹ Some sexual health clinics use rapid tests as an alternative to microscopy and NAATs, as POCT gives results within 30 minutes.¹ This form of testing is only appropriate for vaginal discharge, and should not be used to test urine samples from male patients.¹

Differential Diagnoses

Another obstacle to diagnosing trichomoniasis is that the symptoms are similar to more prevalent conditions, such as bacterial vaginosis.⁹ Table 2 compares the signs and symptoms of bacterial vaginosis and T. vaginalis infection.^{1,2,5,9,10,19,2}

Table 2: Signs and Symptoms of Bacterial Vaginosis and Trichomonas vaginalis Infection^{1,2,5,9,10,19,20}

A brief sexual history, including questions such as ‘Did the discharge or symptoms start after a change in a sexual partner?’ and ‘Have you changed sexual partners in the last 12 months?’ can help clinicians to differentiate between T. vaginalis infection and bacterial vaginosis. It may also be beneficial to consider testing for T. vaginalis in women with recurrent bacterial vaginosis to rule it out as the underlying condition.²⁰

Treatment

Metronidazole is the antimicrobial of choice for T. vaginalis, with a first-line dosage of 400–500 mg twice daily for 7 days.¹ That said, the infection can be difficult to treat, and can recur as a result of inadequate therapy, reinfection, or antimicrobial resistance.¹ It will usually be treated at a sexual health clinic, where treatment success can be more easily assessed, and partner notifications made.¹

If a patient is pregnant or breastfeeding, they must be referred to a sexual health specialist, as special considerations need to be taken into account when treating these women.¹ The guideline also discusses treatment failure and antimicrobial resistance, but these topics are outside the remit of primary care.¹

HIV and T. vaginalis

There are links between HIV-positive status and T. vaginalis infection that have become apparent in global research. HIV makes an individual more susceptible to contracting T. vaginalis, and T. vaginalis infection makes an individual more susceptible to contracting HIV.^1,2 BASHH guidance recommends screening for coexistent STIs in anyone diagnosed with trichomoniasis,¹ and it is good practice to offer HIV testing to anyone who attends for a sexual health screen, particularly in areas of high HIV seroprevalence.²¹

T. Vaginalis and Pregnancy

It is unclear how a person’s vaginal microbiome can negatively affect their pregnancy, but some studies have indicated that T. vaginalis infection may be associated with preterm delivery and low birth weight, and that trichomoniasis at delivery may predispose mothers to postpartum sepsis.¹ In terms of treatment, there is inadequate evidence of the safety of metronidazole in pregnancy, but it has been used for many years without clinical issues.²² Routine screening for T. vaginalis in pregnant women is not currently recommended by BASHH, but it may be in future, especially in groups at higher risk of T. vaginalis infection¹—the infection can be passed from a mother to her baby during childbirth.²³

What Does This Mean for General Practice?

Up to 50% of people infected with T. vaginalis are asymptomatic; nevertheless, BASHH guidance does not recommend widespread screening.¹ The guideline does suggest, however, that screening of asymptomatic women may be appropriate in sexual health clinics in areas of high prevalence, and in women with associated risk factors.¹ Risk factors include older age, current infection with other STIs such as chlamydia or gonorrhoea, and non-White ethnicity.¹

A 2013–2015 study conducted in Bristol, in which samples taken in primary care were screened for T. vaginalis simultaneously to screening for chlamydia and gonorrhoea, found a positivity rate of 2.7% in symptomatic women, and 1.2% in asymptomatic women with STI risk factors.²⁴ Therefore, there is reason to be concerned that cases of T. vaginalis infection are being missed because the infection is not tested for in primary care.²⁴

Barriers to Implementing the BASHH Guideline

There are several challenges facing primary care practitioners trying to follow this guideline, which is oriented towards sexual health settings. The biggest challenge is the low availability of NAATs for T. vaginalis; furthermore, in light of chronic underfunding of sexual and reproductive healthcare services across primary and secondary care, it seems unlikely that availability of these tests will increase. POCT for T. vaginalis may be a solution, but this would necessitate practices or networks investing in testing kits, which may need to be justified based on population and prevalence.

Summary

Trichomoniasis is an often-forgotten STI that can have a negative impact on a patient’s quality of life, as well as potentially poor perinatal outcomes. At present, asymptomatic screening in primary care is not recommended, but anyone presenting with discharge and sexual health risk factors should be offered testing—POCT may be the best way to achieve this in primary care.