Issue: June 2013
June 01, 2013
5 min read

The most common STI you have never heard of

Issue: June 2013
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Trichomonas vaginalis is the most prevalent and treatable sexually transmitted infection in the United States. Up to 7.4 million new cases of T. vaginalis are estimated to occur each year in the United States, but only 30% of those infected develop symptoms. Symptoms can range from mild irritation to severe inflammation, yellow-green vaginal discharge for women, and infertility and urethritis in men. Accurate testing and diagnosis is essential to keep patients from developing significant health problems, including pre-term delivery, low birth weight, infertility, prostatitis and increased risk of HIV acquisition and transmission.

Perils of testing

Although infection is treatable, the most common diagnostic test used to identify T. vaginalis, the wet mount slide exam, detects the infection in only about 50% of cases. New and more advanced screening methods such as amplification assays offer significantly improved sensitivity, detecting 98% of cases.

Many physicians are not aware that the most common testing methods for T. vaginalis are often not accurate. As a result, T. vaginalis remains a significant health risk that is often undiagnosed and largely unrecognized by both health care workers and the general public. Many patients lack access to sensitive testing methods, leaving an estimated 50% of infected people undiagnosed even after screening. In addition, T. vaginalis is not a mandatory reportable STI to public health facilities or part of routine STI screening recommendations, making it even less likely that many patients will have access to an accurate diagnosis. As a result, infections can be chronic and patients can return to health care providers repetitively with the same symptomatic complaints or continue to spread the infection to their sexual partners.

Kimberle C. Chapin

Kimberle C. Chapin

Recent data show that women are more likely to present with symptoms of infection compared with men. In women, infection most commonly affects the lower genital tract including the vagina, vulva or urethra. In men, the most commonly infected part of the body is the urethra. The prevalence of T. vaginalis in men and women varies greatly according to the diagnostic methods used and the population studied. Prevalence rates have been reported as low as 1.7% to as high as 32%.

A recent study with male partners of women with a confirmed diagnosis of trichomoniasis infection found that 72% also were positive for the infection. Among the infected men, 75% did not present with any symptoms. The fact that both men and women are often not screened and that many infections are not properly diagnosed is also believed to contribute to a high rate of reinfection. According to the CDC, 20% of infected people experience a repeat infection 3 months after treatment.

Prevalence in older adults

Although screening for STIs is generally targeted to younger adults, T. vaginalis infection has a high rate of prevalence among men and women aged older than 40 years. In fact, while adolescents and young adults represent the populations at highest risk for STIs overall, recent studies show that the rate of STIs has more than doubled in the past 10 years among those aged 50 to 90 years. Although research to explain the increased rate of STIs among older Americans is limited, both physiology and behavior are likely factors. Hormonal changes may result in an older women being more susceptible to T. vaginalis infection. In addition, as these patients age, chronic infection may result in visible symptoms.

Men may be chronic carriers with no symptoms and more likely to spread infection. Some behavioral factors believed to play a role in transmission include the rising divorce rate, the expanding popularity of online dating, and a lack of concern about pregnancy and risk for STI transmission among older sexually active people.


Awareness of risks associated with T. vaginalis infection is needed among health care providers and the public, including a strong focus on the need for routine screening involving testing procedures that provide more accurate results. Routine proactive screening is especially important because, in many cases, patients can remain asymptomatic for months or years, making it less likely that they will seek or inquire about screening services. In addition, many symptomatic patients are misdiagnosed as having bacterial vaginosis or an infectious disease process that eludes a specific diagnosis. Although the CDC has recommended the use of more sensitive nucleic acid amplification tests for the detection of other STIs, including chlamydia and gonorrhea, it has provided no guidance regarding the preferred testing method in diagnosing T. vaginalis. Misdiagnosis puts patients at risk of either no intervention, allowing infection with T. vaginalis to progress, or inappropriate intervention.

Several diagnostic tests have been introduced in recent years that offer superior sensitivity and specificity compared with the standard low-sensitivity wet mount, including culture methods, non-amplified and nucleic acid amplified tests. Despite strong clinical evidence supporting use of more accurate testing, many health care professionals remain unaware that the most commonly used method of detection has significant limitations in providing an accurate diagnosis.

The need for access to more accurate and rapid testing to confirm T. vaginalis infection is reinforced by the efficacy of currently available treatment options. For most patients, treatment for T. vaginalis infection is noninvasive and routinely successful. A single oral dose of metronidazole or tinidazole, two FDA-approved antibiotics, has been shown to have a very high rate of success in the treatment of T. vaginalis. Despite this success, preventable direct medical costs associated with T. vaginalis infection, including clinician visits, hospitalization, diagnostic testing, drug treatments and therapeutic procedures, now total more than $34.2 million each year, caused largely by lack of access to accurate screening. The lifetime cost of treating T. vaginalis attributable to HIV infections is approximately $167 million, including the cost of antiretroviral medications, inpatient and outpatient care and other HIV-related medications and laboratory costs.

Strategies for success

Addressing the challenges associated with T. vaginalis requires a two-pronged strategy. Facilities and health care workers must take steps to expand awareness of the risk and promote optimal testing protocols. At the same time, health care systems must expand awareness of the risks among patients, including a focus on the need for both partners to be tested to reduce the risk for repeat TV infection.

Many clinicians compare current standards in T. vaginalis awareness and treatment to those associated with HPV 10 years ago. At that time, health care workers and patients were largely unaware of the risk and incidence of infection with HPV, but several research studies confirmed a link to cervical cancer. Research also indicated that routine Pap smears could play an important role in HPV diagnosis. Based on the findings, efforts in targeted patient and physician education led to more aggressive prevention and intervention strategies that have in turn led to a drop in cervical cancer rates overall.

Similar efforts related to T. vaginalis screening will require outreach to health care workers, laboratories and the general public, especially targeting people aged older than 40 years, about the need for routine screening that involve more accurate assays to detect STIs. In addition, public health policies must be amended to position T. vaginalis infection as a reportable STI, and testing guidelines need to be put in place to help physicians and labs better detect the disease. Public awareness campaigns must work to reinforce the fact that this is a potentially dangerous infection that can lead to severe health problems, including higher risk for HIV transmission, infertility and, even potentially, prostate cancer in men.


With both technologies that can work to improve accuracy in diagnosis and readily available and effective treatment options, these strategies can play a significant role in reducing the health risks associated with T. vaginalis infection in the next decade.

See the references online at

Kimberle C. Chapin, MD, is an professor of Pathology and Medicine at the Medical School of Brown University and Director of Microbiology at Lifespan Medical Center Department of Pathology in Rhode Island. Chapin serves on the CDC Clinical Laboratory Improvement Advisory Committee, is the past chair of the American Board of Medical Microbiology and the American Academy for Microbiology Standards and Examination Committee. She can be reached at

Disclosure: Chapin is a paid consultant for BD Diagnostics and Hologic. She has received grant support and served on advisory committees.