PROTOZOAL STI / CARE & TRANSMISSION
Trichomonas vaginalis
Trichomoniasis is a treatable genital infection caused by a microscopic parasite. Many people have little or no discomfort. Treating current partners at the same time, and retesting later, stops it passing back and forth. [24]
Transmission risk
Risk by type of contact
Bottom line. Trichomoniasis is primarily a genital infection transmitted through sexual contact. The high positivity sometimes reported among partners is not a measured probability of acquiring it from one act.
General
Oral
Vaginal
Anal
Kissing
What changes the risk (3)
- Partner positivity is not acquisition probability. MEDIUM: 205/280 (73.2%) male partners of infected women tested positive in Hobbs 2006; this does not prove who infected whom or a 73.2% per-act/per-partnership acquisition rate. Sources 2
- Treatment and reinfection. LOW for numerical risk effect: treating infection and infected partners matters; persistent or recurrent infection may reflect resistance, nonadherence or re-exposure. Sources 1
- Other prevention. LOW: no validated oral/anal multipliers for ejaculation, menstruation or concurrent STIs; doxy-PEP is not an established trichomoniasis prevention method and there is no licensed vaccine. Sources 1, 3
Condoms and dental dams
CDC recommends consistent, correct condoms; no robust infection-specific, route-stratified numerical efficacy estimate was verified. Dental-dam clinical efficacy is unmeasured. Evidence: Low Sources 1
Sources for this risk profile (3)
- CDC CDC, 2021. Trichomoniasis - STI Treatment Guidelines. cdc.gov
- Hobbs MM et al. Journal of Clinical Microbiology, 2006. Methods for Detection of Trichomonas vaginalis in the Male Partners of Infected Women: Implications for Control of Trichomoniasis. DOI: 10.1128/JCM.00952-06. journals.asm.org
- Bachmann LH et al.; CDC MMWR Recommendations and Reports, 2024. CDC Clinical Guidelines on the Use of Doxycycline Postexposure Prophylaxis for Bacterial Sexually Transmitted Infection Prevention, United States, 2024. DOI: 10.15585/mmwr.rr7302a1. cdc.gov
* How to read these figures. Each is a published estimate under the conditions shown beside it, usually an untreated partner and a single act or partnership. It is not a prediction of your personal risk.
- Evidence: High
- Several prospective studies or a systematic review broadly agree.
- Evidence: Medium
- One or two studies, wide uncertainty, or a model.
- Evidence: Low
- Guideline judgment, case reports, or extrapolation.
Where no risk level is shown, the evidence cannot rank it. That is not the same as low.
Evidence reviewed through 2026-10-27. For reference only; not medical advice.
When to test after a possible exposure
No universally validated post-exposure rule-out interval; test when clinically indicated rather than using the symptom incubation period as a countdown.
When to be seen sooner. Genital symptoms or a diagnosed partner warrant evaluation now.
-
Trichomonas NAAT / other validated diagnostic method
No precise universally reliable exposure-to-positive day was established in the reviewed guidance.
Testing fits symptoms or a confirmed contact; current partners of someone diagnosed are usually offered treatment without waiting for a screening window.
Specimens: Vaginal specimen; Urine or other specimen validated for the assay and anatomy
Sources 1
Early negatives, after treatment, and screening limits
An early negative result. An early negative does not exclude very recent acquisition. Repeat testing is individualized if concern remains; do not turn a broad postexposure protocol into a proven detection threshold.
After treatment. If NAAT is used for persistent/recurrent infection, CDC advises not before 3 weeks after treatment completion. Retesting sexually active women around 3 months is for reinfection. The three-week interval is not a post-exposure testing window.
Screening limits. Routine screening of everyone is not recommended; selected populations and clinical contexts differ.
Kissing and body sites. Routine throat/rectal testing is not recommended; there is no validated screening schedule after kissing.
Sources for testing guidance (1)
- CDC STI Treatment Guidelines. Trichomoniasis: diagnosis and recurrent infection. 2021. cdc.gov
Treatment
Nitroimidazole antibiotics, usually metronidazole or tinidazole, are effective. CDC generally recommends a seven-day metronidazole course for women and a single dose for men; the clinician adapts treatment to anatomy, pregnancy, tolerance and prior failure. Persistent infection needs assessment for reinfection, adherence and resistance. [24]
Actions
1. Use a sensitive test. A vaginal NAAT or another validated genital/urine assay is usually more sensitive than microscopy. A negative wet mount does not reliably exclude infection. Routine throat or rectal swabs are not indicated. [24]
2. Include current partners. Current sexual partners are usually offered evaluation and treatment at the same time. There is no single lookback period for every situation; the clinic defines it. [24]
3. Pause, then retest. Wait to have sex until everyone being treated has finished and symptoms have settled. Sexually active women are usually retested at about three months. For persistent infection, a repeat NAAT waits until at least three weeks after finishing treatment. [24]
SCIENCE & CONTEXT
Trichomoniasis / the evidence
History
T. vaginalis was described in 1836. Early clinical work established its presence in genital infection, including in men. Metronidazole changed treatment in the mid-20th century; clinical studies were reporting its use by the early 1960s. Modern molecular tests reveal infections that microscopy can miss. [24][25][26]
Impact
This single-celled organism can inflame the vagina or urethra. Discharge, irritation, or pain when urinating or during sex can occur, but an estimated 70-85% have few or no symptoms. Without treatment it can last for months or longer. It is linked with some pregnancy complications and a higher chance of acquiring HIV; those links are population findings, not a prediction for any one person. [24]
Because infection can persist and partners may have no symptoms, a new diagnosis does not precisely date acquisition. Recurrent positivity is often related to reinfection, but clinical review is needed before assuming the same explanation for everyone. [24]
Probability at a glance
Chance that at least one recent partner has trichomoniasis, by number of partners in six months, in three measured settings. This is not your chance of getting it.
| Partners | 0.5% scenario | 2.1% scenario | 14.6% scenario |
|---|---|---|---|
1-2 | 0.5–1.0 | 2.1–4.2 | 14.6–27.1 |
3-5 | 1.5–2.5 | 6.2–10.1 | 37.7–54.6 |
6-10 | 3.0–4.9 | 12.0–19.1 | 61.2–79.4 |
11-20 | 5.4–9.5 | 20.8–34.6 | 82.4–95.7 |
Illustrations use CDC-cited prevalence in US men (0.5%), US women (2.1%) and women in selected STI clinics (14.6%). They are different sampling frames, not interchangeable personal risk tiers. [24]
In short: trichomoniasis can be common in some settings and is readily treated. Treating current partners together matters more than any label for a community.