Trichomoniasis: The Most Common STD

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Trichomoniasis : Background Trichomoniasis : Treatment
Trichomoniasis : Signs and Symptoms Trichomoniasis : Prevention
Trichomoniasis : Complications Trichomoniasis : References
Trichomoniasis : Diagnosis


TrichomoniasisMost likely, you’re very familiar with STDs such as HIV, gonorrhea, syphilis, and herpes. But have you ever heard of trichomoniasis? Probably not. Surprisingly, trichomoniasis (nicknamed “trich”or “trick”) is the most common sexually transmitted infection in the world. Caused by a microscopic parasite called Trichomonas vaginalis, the disease affects approximately 275 million people worldwide. The U.S. Centers for Disease Control (CDC) estimates that over 3% of the population is infected at any one time. Like most other STDs, the parasite is transmitted via the body fluids of an infected person to an uninfected person during sexual intercourse without a condom.

Because trichomoniasis is a sexually transmitted disease, it occurs more frequently in individuals who have multiple sexual partners. It often occurs simultaneously with other sexually transmitted diseases, especially gonorrhea. Although both men and women are susceptible to the disease, infection is more common in women. In the United States, the highest number of cases are seen in women between age 16 and 35. A woman is most susceptible to infection just after having completed her menstrual period.

Signs and Symptoms

About 70% of infected people do not experience any symptoms. Trichomonas parasites can survive in the vagina for many years without causing symptoms. (However, the parasite cannot live in the mouth or rectum.) When the disease causes symptoms, they can range from mild irritation to very severe inflammation and pain. The symptoms usually appear within 5 to 28 days of exposure.

Trichomoniasis typically infects the vagina of women and the urethra (urine passageway) of men, although symptoms can also appear in the cervix. In women, symptoms can include a greenish or yellowish vaginal discharge with an unusual smell, vaginal itching or pain, redness and inflammation around the vaginal opening, painful sexual intercourse, and burning during urination (Health A-to-Z). Some women also experience lower abdominal discomfort.

Most men with trichomoniasis do not have any signs or symptoms. Some men may feel irritation, burning, or pain in the penis during urination or ejaculation, frequent urination, or an unusual discharge from the penis. In addition, the tip of the penis and the prostate gland can become infected.

Without treatment, the infection can last for months and sometimes even years. The use of antibiotics is a contributing factor to recurrent trichomoniasis in some women because antibiotics kill off the normal “good” bacteria in the vagina, allowing organisms such as Trichomonas vaginalis to multiply more rapidly.


Trichomoniasis can facilitate the transmission of other sexually transmitted infections, especially HIV. Research has shown that it is easier for HIV to pass into the bloodstream when inflammation is present. Since trichomoniasis can cause inflammation of the vagina and penis, it can provide an easy route for HIV to enter the body. In addition, because trichomoniasis can cause an increase in the HIV viral load in semen and vaginal fluid, there is greater risk of passing the HIV virus to a sexual partner.

In pregnant women, trichomoniasis can increase the risk of premature rupture of the membranes and preterm delivery. Infants born to infected mothers are more likely to have a low birth weight (less than 5.5 pounds). In addition, trichomoniasis has been associated with an increased risk of inflammation of the fallopian tubes.

Like all STDs, trichomoniasis can have devastating emotional consequences, including depression, loss of self esteem, anger, betrayal, and even thoughts of suicide. Very often, the psychological trauma will continue long after the disease itself has been successfully treated.

There has been recent evidence that men with a history of trichomoniasis are more likely to develop prostate cancer. A study conducted in 2009 by the Harvard School of Public Health (Journal of the National Cancer Institute, 2009; 101:1406-11) found that a quarter of men with prostate cancer showed signs of trichomoniasis. In addition, these men were more likely to have advanced tumors, possibly indicating that trichomoniasis causes cancer cells to grow more rapidly.

Even more recently, a laboratory study conducted by researchers from the University of California (published in 2014 in the journal Proceedings of the National Academy of Sciences) found that the parasite that causes trichomoniasis appears to produce a protein that is similar to a human protein involved in inflammation and increased growth of benign and cancerous prostate cells. Although these are certainly interesting results, it is important to note that this was a laboratory study and did not involve any men with benign enlargement of the prostate or prostate cancer. Additional studies are needed to determine whether there is a clear link between trichomoniasis and prostate cancer. Furthermore, we should certainly not jump to the conclusion that prostate cancer is a sexually transmitted disease. It is very likely that trichomoniasis is just one of a series of risk factors rather than a single definitive cause.


After you report your symptoms, your health care provider will do a pelvic examination and check your vagina or urethra for inflammation and abnormal discharge. In women, small red sores may be visible inside the vagina or on the cervix. A specimen of vaginal or penile discharge will be collected using a cotton-tipped applicator. The specimen is placed on a microscopic slide and sent to a laboratory for examination. Trichomonas vaginalis parasites – wiggling organisms with 4 flagella (tails) extending from the cell mouth – can be easily identified, although microscopic examination does not identify all infections, since large numbers of parasites must be present. Because patients with trichomoniasis are more likely to contract other STDs, your health care provider may also perform tests for HIV, gonorrhea, chlamydia, and hepatitis B (Health A-to-Z).


Fortunately, trichomoniasis can be treated very effectively in 90% to 95% of cases. The most common treatment is an oral agent called metronidazole (Flagyl, Metryl, Protostat). All sexual partners of an infected individual must be treated to prevent the infection from being passed back and forth. Sexual intercourse should be avoided until all partners are cured. Pregnant women can take metronidazole, even during the first trimester of pregnancy, according to the CDC. In people who drink alcoholic beverages, metronidazole can trigger cramps, severe nausea and vomiting, and headaches. To prevent these problems, avoid alcohol while taking metronidazole and for at least 3 days after you stop taking the drug.

In the 2000s, the number of cases of metronidazole-resistant trichomoniasis increased rapidly, so the use of another oral antibiotic – tinidazole (Tindamax) – has been increasing. As with metronidazole, alcohol should be avoided while taking the drug since cramping and stomach upset can occur. Some health care professionals have also successfully treated patients with the broad-spectrum anti-parasitic drug nitazoxanide (commonly used to treat diarrhea in children and adults), but further research needs to be done.

For most people, the symptoms go away within 1 week after treatment. Men who are infected may stop having symptoms in a few weeks even without treatment. However, without treatment they can keep infecting their partners, so it is essential that treatment is administered.

Although not recommended by the CDC, other homeopathic treatments are occasionally suggested. Some practitioners suggest dietary changes such as avoiding sweets and carbohydrates. Others may advocate vitamin and mineral supplements, including vitamins A, C, and E, and zinc. Naturopaths may recommend treatment with herbal douches or douches containing live acidophilus cultures, boric acid, or vinegar.


Because trichomoniasis is transmitted during sexual activity, the most reliable way to prevent infection is to abstain from oral, vaginal, and anal sex or to have sex with only one uninfected sex partner who is not sexually active with anyone else. When used consistently and correctly, male latex or polyurethane condoms are also highly effective in preventing the sexual transmission of infection. Condoms should be used for all types of sexual contact, even if penetration does not occur, and a new condom should be after each ejaculation.

Most other birth control methods – including the pill, IUD, diaphragm, and spermicides – don’t protect against trichomoniasis and other STDs. Washing genitals and douching after sex are not reliable preventive measures.

If you have had sex without a condom and are worried that you may have been infected, you should see your doctor or healthcare provider even if you don’t have symptoms. If either you or your partner have had other sexual partners in the past, get tested before becoming sexually active.

If young children and teenagers show signs of trichomoniasis, it may be a sign of sexual abuse. Tell a caregiver immediately if you suspect sexual abuse.


1) Trichomoniasis – CDC Fact Sheet.
Source: Centers for Disease Control and Prevention

2) Prostate cancer ‘may be a sexually transmitted disease’
Source: BBC News Health. May 19, 2014.

3) Is Prostate Cancer Really a Sexually Transmitted Disease?
Source: Steve Williams May 26, 2014

4) Prospective Study of Trichomonas vaginalis Infection and Prostate Cancer Incidence and Mortality: Physicians’ Health Study.
Source: Jennifer R. Stark et al, J Natl Cancer Inst. 2009;101(20):1406-11.

5) Trichomoniasis.

6) Trich: The Most Common Sexually Transmitted Infection You May Never Have Heard Of RH
Source: Reality Check. February 22, 2013.

7) Trichomoniasis
Source: Aetna InteliHealth

Posted in STI.