Trichomoniasis is one of the most common sexually transmitted infections in the world. Globally, there were roughly 156 million new cases in 2020 among people aged 15 to 49. In the United States alone, the CDC estimated more than two million infections in 2018. Despite those numbers, trichomoniasis flies under the radar compared to infections like chlamydia and gonorrhea, partly because most people who have it don’t know it.
How It Compares to Other STIs
Trichomoniasis is caused by a parasite rather than a bacterium or virus, which makes it unique among common STIs. But in terms of sheer numbers, it sits alongside chlamydia, genital herpes, and HPV at the top of the list. Together, those four infections accounted for 98% of all prevalent STIs and 93% of all new STIs in the U.S. in 2018, according to CDC estimates. Chlamydia gets far more attention because routine screening is standard practice, but trichomoniasis generates a comparable volume of infections each year.
Who Gets It Most Often
A nationally representative study of U.S. adults aged 18 to 59 found trichomoniasis in 1.8% of women and 0.5% of men overall. Those averages mask a stark racial disparity: prevalence among Black women was 8.9%, and among Black men it was 4.2%. For all other racial and ethnic groups combined, the rates were 0.8% in women and 0.03% in men. Researchers attribute this gap not to biological differences but to structural factors like unequal access to screening, treatment, and follow-up care, along with the reality that a higher background prevalence in a sexual network increases any individual’s exposure risk.
Age matters too, though less dramatically. Prevalence was lowest in the 18 to 24 age group (0.7%) and peaked among adults 25 to 39 (1.4%). Unlike chlamydia, which skews heavily toward younger people, trichomoniasis stays relatively common through middle age.
Most Infections Have No Symptoms
A major reason trichomoniasis is so widespread is that the majority of infected people never develop noticeable symptoms. Estimates vary, but roughly 70% to 85% of cases produce no itching, discharge, or discomfort. Men are especially unlikely to feel anything wrong, which means they can unknowingly pass the parasite to partners for weeks or months. Even in women who do develop symptoms, the signs (yellowish-green discharge, irritation, pain during urination) can be mild enough to dismiss or mistake for a yeast infection.
This silent spread is compounded by the fact that trichomoniasis is not included in most standard STI panels. Unless a provider specifically orders testing for it, the infection simply won’t be detected during a routine screening visit. That testing gap helps explain why millions of cases circulate undiagnosed each year.
Reinfection Is Surprisingly Common
Even after successful treatment, getting trichomoniasis again is a real and frequent problem. Among women who were retested within three months of their initial treatment, 24% tested positive again. For pregnant women, that number climbed to 33%. Reinfection typically happens because a sexual partner wasn’t treated at the same time, so the parasite simply passes back and forth. The body does not develop immunity after clearing the infection, so you can catch it as many times as you’re exposed.
Because of these high reinfection rates, the CDC recommends retesting all sexually active women about three months after their initial treatment, regardless of whether their partners were also treated. In practice, many patients don’t return for that follow-up test, which allows reinfections to go undetected and continue spreading.
Why It Matters Beyond Discomfort
Trichomoniasis is easy to treat with a course of oral antibiotics, which can make it seem like a minor nuisance. But untreated infections carry real consequences. The parasite causes inflammation in the genital tract, which makes it easier to acquire or transmit HIV. For people already living with HIV, an active trichomoniasis infection can increase the amount of virus in genital secretions.
In pregnancy, the stakes are higher. A large meta-analysis found that trichomoniasis was associated with 27% higher odds of preterm delivery and more than double the odds of low birth weight. The risk of the membranes rupturing before labor was 87% higher in women with the infection. These aren’t rare complications in absolute terms, because trichomoniasis is common enough in pregnant populations that a meaningful number of adverse birth outcomes may be linked to it.
Men and the Gender Gap in Diagnosis
Global estimates from 2020 actually show more new infections in men (82.6 million) than in women (73.7 million), which may surprise anyone who thinks of trichomoniasis as primarily a women’s health issue. The difference in detected prevalence, where women test positive far more often, largely reflects the fact that men are almost never screened. The parasite tends to clear on its own in men more readily than in women, but during the weeks or months it persists, an infected man can still transmit it. There is currently no FDA-approved test for trichomoniasis in men that is widely used in routine clinical practice, which keeps male infections largely invisible in surveillance data.
This diagnostic blind spot creates a frustrating cycle. Women get treated, their untested male partners remain infected, and reinfection follows. Treating both partners simultaneously is the most effective way to break the chain, but it requires providers to prescribe treatment for a partner who may never have been tested.