The Facts About Trichomoniasis and HIV

Common Sexually Transmitted Infection May Double the Risk of HIV

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Trichomoniasis is a sexually transmitted infection caused by a one-celled parasite called Trichomonas vaginalis. It's estimated that 7.4 million men and women get trichomoniasis each year.

This common sexually transmitted disease affects both men and women; however, symptoms are more common in women, appearing in about 50% of those who are infected.

In men, infection lasts only a short time and is usually urethral, meaning it affects primarily the urinary tract.

While the infection in men lasts only a short time, infected men can easily transmit the parasite to a female partner.

Because the parasite does not survive in either the mouth or the rectum, trichomoniasis is spread from person to person during unprotected sexual intercourse.

In women, the most common site of infection is the vagina, while the urethra (urinary tract) is the most common infection site for men. Women can get infected by men or women through direct sexual contact, while men are most commonly infected by women.


If trichomoniasis signs and symptoms do occur, they usually appear within four weeks of exposure.

In women, the most common signs of infection are:

  • Genital inflammation
  • Foul-smelling, yellow-green vaginal discharge
  • Pain with intercourse and/or urination
  • Itching and irritation of the vagina and thighs
  • Abdominal pain (less common)

Most men will have few or no symptoms after being infected with T. vaginalis.

However, if they, they are usually mild and short-lasting. The most common symptoms in men include:

  • Irritating sensation "inside" the penis
  • Penile discharge
  • Burning after urination and/or ejaculation

Association With HIV

Women with genital inflammation, including inflammation due to trichomoniasis, have an increased risk of HIV infection.

Furthermore, trichomoniasis infection in HIV-positive women increases the risk of passing HIV to male sexual partners.

Studies suggest that the prevalence of trichomoniasis in women with HIV runs anywhere from 10% to 20%, and that T. vaginalis is emerging as one of the most important cofactors in amplifying HIV risk, particularly in African American communities.In fact, trichomoniasis is the most common sexually transmitted infection with African American women, primarily those in major urban centers.

Some African studies have suggested that trichomoniasis may increase the likelihood of HIV transmission by approximately twofold.


Women are easily treated with a single dose of an oral antibiotic called Flagyl (metronidazole). While most doctors prefer to treat with a single dose, dosages can vary based on the case, as follows:

  • 2 grams of Flagyl, taken as a single dose
  • 500 milligrams twice daily for seven days
  • 250 milligrams three times daily for seven days

In men, trichomoniasis infection will usually go away without treatment. However, because men are often unaware of their infection, they can potentially re-infect their female partners over and over again. Therefore, both partners should be treated concurrently if either is diagnosed, halting the cycle of reinfection.

Flagyl should not be taken if the person has been drinking alcohol as metronidazole prevents the breakdown of alcohol in the liver. As a result, symptoms such as vomiting, nausea, headaches, and stomach cramps can occur. To avoid these side effects, it is best to avoid alcohol for at least 24 hours of starting and 24 hours of taking a Flagyl dose.


Preventing trichomoniasis is not unlike the prevention of any other sexually transmitted infection. Whether or not there are outward symptoms, it is still best to follow basic safer sex guideline, including:

  • Using latex condoms during each and every sexual encounter, especially during vaginal intercourse.
  • If a trichomoniasis infection is expected, sexual activity should stop until treatment of the infected person and their sexual partners is completed and all symptoms have resolved.

Finally, if you are in a serodiscordant relationship (where one partner has HIV and the other doesn't), it should not be presumed that the HIV prevention pill (PrEP) and/or HIV therapy will allow for condom-less sex. This is particularly true if either partner has a sexually transmitted infection, which can greatly increase the potential for HIV transmission.


Centers for Disease Control; "Trichomoniasis Fact Sheet"; U.S. Department of Health and Human Services; 2007.

Sorvillo, F.; Smith, L.; Kendt, P.; et al. "Trichomona vaginalis, HIV, and African Americans." Emerging Infectious Diseases. December 2001; 7(6): DOI:10.320/eid0706.010603.