Trichomoniasis comes from a single-celled parasite called Trichomonas vaginalis, and it spreads almost exclusively through sexual contact. It is the most common curable sexually transmitted infection in the world, with roughly 156 million new cases globally in 2020. Unlike bacteria or viruses, this parasite is a protozoan, a tiny organism with whip-like tails called flagella that it uses to move through the genital tract and attach to tissue.
The Parasite Behind the Infection
Trichomonas vaginalis is a pear-shaped organism so small it can only be seen under a microscope. It has five flagella that propel it through moist environments in the body. It cannot form a protective shell or spore the way some other parasites can, which means it dies quickly in dry conditions. This is a parasite that depends entirely on the warm, wet environment of the human genital tract to survive and reproduce.
Because it lacks a dormant stage, Trichomonas vaginalis is fragile outside the body. It can survive in moist conditions like urine, semen, or swimming pool water for 6 to 24 hours, and only about 30 to 45 minutes when directly exposed to air. On dry surfaces, it dies within several hours. This fragility is a key reason the infection is overwhelmingly transmitted through direct sexual contact rather than casual means.
How It Spreads Between People
The parasite passes from one person to another during unprotected sex. It typically spreads from a penis to a vagina, from a vagina to a penis, or from one vagina to another. The parasite does not commonly infect the hands, mouth, or anus.
In women, the infection settles in the lower genital tract: the vulva, vagina, cervix, or urethra. In men, it lives inside the urethra and can also inhabit the prostate. This difference in where the parasite takes up residence helps explain why men and women experience the infection so differently.
Why So Many Cases Go Unnoticed
One of the most important things to understand about trichomoniasis is that it often produces no symptoms at all. More than half of infected women develop vaginal discharge, but that still leaves a large portion who feel perfectly fine. In men, the numbers are even more striking: only about 10% develop urethral discharge or pain when urinating. The vast majority of men carry the parasite without knowing it.
This silent nature is what makes trichomoniasis so widespread. People who don’t know they’re infected continue having sex and passing the parasite to new partners. Someone can carry the infection for weeks, months, or even longer before it’s detected, either through symptoms finally appearing or through routine testing.
Can You Get It Without Sexual Contact?
Non-sexual transmission is rare but not impossible. There are documented cases involving contaminated objects like douche nozzles, damp washcloths, medical instruments, and toilet seats. These cases are uncommon precisely because the parasite is so fragile. It needs moisture to survive, and most everyday surfaces dry out too quickly to keep it alive.
If you’ve been diagnosed with trichomoniasis and haven’t had a new sexual partner, it’s worth knowing that the infection can remain dormant and undetected for a long time. A positive test doesn’t necessarily mean recent exposure. It may reflect an older infection that was never caught.
Who Is Most at Risk
Anyone who is sexually active can get trichomoniasis, but certain factors raise the likelihood. Having multiple sexual partners, not using condoms, and having a history of other sexually transmitted infections all increase risk. Having another STI, particularly HIV, can make a person more vulnerable to picking up the parasite. The reverse is also true: trichomoniasis can make it easier to acquire or transmit HIV, because the inflammation it causes creates more entry points for the virus.
Women are diagnosed more often than men, partly because the infection is more likely to cause noticeable symptoms in women and partly because testing in men has historically been less common. However, global estimates suggest men actually account for slightly more new infections each year, with about 82.6 million male cases compared to 73.7 million female cases in 2020.
How It Gets Diagnosed
The traditional method involves placing a swab sample on a slide and examining it under a microscope while it’s still wet. This approach is cheap and fast, but it only catches 44% to 68% of infections, and its accuracy drops sharply if the sample isn’t examined immediately. Within an hour, detection rates fall to around 20%.
Molecular tests that detect the parasite’s genetic material are far more reliable, with sensitivity above 95% and specificity near 100%. These tests can be run on vaginal swabs, cervical swabs, or urine samples. Some versions deliver results in under an hour. If you’re being tested and receive a negative result from a microscope exam alone, it’s worth asking about molecular testing to confirm.
Why It Keeps Circulating
Trichomoniasis persists as a global health problem for a few reinforcing reasons. The parasite produces no symptoms in most men and many women, so people unknowingly spread it. Routine STI screening panels often don’t include trichomoniasis unless it’s specifically requested. And unlike some infections, having trichomoniasis once doesn’t create immunity. You can be reinfected immediately after treatment if an untreated partner passes the parasite back. This cycle of silent carriage, incomplete screening, and reinfection is what keeps the numbers so high worldwide.