STI Quarterly

Test now for trichomonas infection: New data shows spread of disease

Infection more than twice as common in women over age 40

Trichomoniasis, caused by the parasite Trichomonas vaginalis, is the most common sexually transmitted infection (STI) in the nation, with an estimated 7.4 million men and women newly infected each year.1

New study evidence now indicates the STI is more than twice as common in women over 40 than previously thought.2 Among 7,593 U.S. women between ages 18-89, women 50 and older had the highest trichomonas infection rate, at 13%, with 11.3% of women in their 40s testing positive for the infection. In comparison, adolescents ages 18-19 recorded an 8.5% infection rate.2 The study, which collected test samples from women in 28 states, is believed to be the largest and most in-depth analysis of the STI ever performed.

"We usually think of STIs as more prevalent in young people, but our study results clearly show that with trichomonas, while too many young people have it, even more, older women are infected," says Charlotte Gaydos, MS, DrPH, professor of medicine in the Division of Infectious Diseases at Johns Hopkins University in Baltimore, MD, and senior study investigator.

Trichomonas infections are quite treatable with antibiotics, says Gaydos. The high numbers of infections found in the current study warrant older women getting screened by family physicians and gynecologists during routine check-ups to make sure they are not infected and are not inadvertently spreading it to others, she states.

Clinicians are not aware that new research indicates that trichomonas infection has been associated with HIV acquisition,3,4 says Gaydos. It also is highly associated with adverse birth outcomes, such as low birth weight and premature rupture of membranes,5 she notes. With current evidence now in hand, trichomonas infection should now be added to the list of reportable STIs, says Gaydos.

STI gets no respect

However, trichomonas is the "Rodney Dangerfield" of the STIs in the way it is perceived by clinicians and often by laboratory people as well, says Marcia Hobbs, PhD, research associate professor of medicine, microbiology, and immunology at the University of North Carolina at Chapel Hill School of Medicine. Hobbs, a molecular microbiologist, presented on the subject at the Quebec City conference.6

Because it is not a bacteria or a virus, for many people, trichomonas "falls off the radar" in terms of being an important microorganism and pathogen, Hobbs observes. Given that it is more difficult to manipulate in the laboratory, inadequate and insensitive diagnostics have been developed to detect it, she notes.

Why hasn't more attention been given to detecting trichomonas infection? Hobbs uses the analogy of looking for missing car keys under a street light, not because the keys were lost in that location, but that the light is shining there. "We know how to look for other things, and we look for what we know how to look for," she observes. "Because we haven't had very good tools to look for trichomonas, we therefore have not looked for it, and so we don't really know a lot about it."

Gaydos agrees with Hobbs' assessment and notes that available tests in the past have included wet preparation, which offers about 50% sensitivity, and culture, which takes several days and is only about 70% sensitive. Thus, if no one tests, or uses a substandard test, not many receive treatment, says Gaydos.

New test now available

Testing for trichomonas might change with the advent of a new assay. Gen-Probe of San Diego received approval in April 2011 from the Food and Drug Administration (FDA) for its Aptima Trichomonas assay for use on its fully automated Tigris system.

Results of the clinical trial used to gain FDA clearance for the assay were presented at the Quebec City conference. To perform the study, researchers tested 933 women attending nine obstetric/gynecology, adolescent, family planning or sexually transmitted disease clinics in the United States. Data indicates sensitivity of the assay was high in all specimens tested and much higher than that usually reported for wet mount and culture, researchers report.7 The amplified nucleic acid assay may be used to test clinician-collected endocervical or vaginal swabs, urine, and specimens collected in PreservCyt solution from symptomatic or asymptomatic women.

STI is often silent

While trichomonas infection can cause symptoms such as vaginitis and cervicitis in women and urethritis in women and men, in most cases, the infection is asymptomatic.8

Because confirmed cases of trichomonas infection do not have to be reported to local public health officials and the Centers for Disease Control and Prevention (CDC), public health officials are not made aware how prevalent it really is, observes Gaydos.

Treatment of the infection is simple, says Hobbs. The CDC recommended regimens for trichomoniasis treatment call for metronidazole, 2 g orally in a single dose, or tinidazole, 2 g orally in a single dose.9 An alternate regimen is metronidazole, 500 mg orally twice a day for seven days. Advise patients to avoid consuming alcohol during treatment with metronidazole or tinidazole; abstinence from alcohol use should continue for 24 hours after completion of metronidazole or 72 hours after completion of tinidazole.9

Resistance to metronidazole is on the rise,10 says Hobbs. Trichomonas is a microorganism that has the ability to change its genetic coding capacity; therefore, it will evolve resistance as time goes on, she notes. "Development of new treatments is definitely going to be needed," says Hobbs. "Because the more we look for it and treat, the more likely resistance is to emerge."


  1. Centers for Disease Control and Prevention. Trichomoniasis. Fact sheet. Accessed at
  2. Ginocchio CC, Chapin K, Smith JS, et al. Prevalence of Trichomonas vaginalis and coinfection with Chlamydia trachomatis and Neisseria gonorrhoea in the USA as determined by the Aptima Trichomonas vaginalis nucleic acid amplification assay. Presented at the International Society for STD Research. Quebec City, Canada; 2011.
  3. McClelland RS, Sangare L, Hassan WM, et al. Infection with Trichomonas vaginalis increases the risk of HIV-1 acquisition. J Infect Dis 2007; 195:698-702.
  4. Mavedzenge SN, Pol BV, Cheng H, et al. Epidemiological synergy of Trichomonas vaginalis and HIV in Zimbabwean and South African women. Sex Transm Dis 2010; 37:460-466.
  5. Cotch MF, Pastorek JG 2nd, Nugent RP, et al. Trichomonas vaginalis associated with low birth weight and preterm delivery. The Vaginal Infections and Prematurity Study Group. Sex Transm Dis 1997; 24:353-360.
  6. Hobbs, MM. Trichomoniasis: why is it the neglected STD? Presented at the International Society for STD Research. Quebec City, Canada; 2011.
  7. Schwebke JR. Clinical evaluation of the Aptima trichomonas vaginalis assay in asymptomatic and symptomatic female subjects. Presented at the International Society for STD Research. Quebec City, Canada; 2011.
  8. Hobbs MM, Kazembe P, Reed AW, et al. Trichomonas vaginalis as a cause of urethritis in Malawian men. Sex Transm Dis 1999; 26:381-387.
  9. Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines, 2010. MMWR 2010; 59(RR12);1-110.
  10. Dunne RL, Dunn LA, Upcroft P, et al. Drug resistance in the sexually transmitted protozoan Trichomonas vaginalis. Cell Res 2003; 13:239-249.