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Approach to trichomoniasis

Last updated 22 Mar 2026 · STD

Assessment of Trichomoniasis

Introduction & Australian Epidemiology

Trichomoniasis is the most common non-viral sexually transmitted infection (STI) globally, caused by the protozoan parasite Trichomonas vaginalis. In Australia, trichomoniasis disproportionately affects Aboriginal and Torres Strait Islander (ATSI) communities, particularly in remote areas, with prevalence rates up to 10-fold higher than non-Indigenous populations. The infection is more common in women than men and increases the risk of HIV acquisition and transmission.

ℹ️
Epidemiological Note: ATSI women in remote communities have trichomoniasis prevalence rates of 15-30%, compared to 1-3% in urban non-Indigenous populations. This disparity reflects complex social determinants of health including overcrowding, limited access to healthcare, and higher rates of partner concurrency.

Pathophysiology & Microbiology

Trichomonas vaginalis is a flagellated protozoan parasite that colonizes the urogenital tract. The organism adheres to epithelial cells via surface proteins and causes direct cytotoxic damage through proteolytic enzymes. Unlike other STIs, T. vaginalis can survive in chlorinated water and on damp surfaces for short periods, although sexual transmission remains the primary route of infection.

Microbiological Characteristics
  • Flagellated protozoan, 10-25 μm in length
  • Anaerobic metabolism with hydrogenosomes
  • No cyst stage - only trophozoite form
  • Optimal pH 6.5-7.0, temperature 35-37°C
  • Dies rapidly outside host (hours to days)
Virulence Factors
  • Adhesins for epithelial cell binding
  • Cysteine proteases causing cell damage
  • Complement resistance factors
  • Iron acquisition mechanisms
  • pH modification capabilities

Clinical Presentation & Diagnostic Criteria

Trichomoniasis presents differently in women and men, with women more likely to be symptomatic. Up to 50% of infected individuals may be asymptomatic, particularly men, making screening important in high-risk populations.

WOMEN
Symptomatic Infection
Classical triad (20-30% of cases):
  • Frothy, yellow-green vaginal discharge
  • Vulvar pruritus and burning
  • "Strawberry cervix" (punctate hemorrhages)
Other symptoms:
  • Dysuria and urinary frequency
  • Dyspareunia
  • Offensive vaginal odor
  • Post-coital bleeding
MEN
Often Asymptomatic
When symptomatic:
  • Urethral discharge (usually scant, clear)
  • Dysuria
  • Urethral irritation
  • Rarely: epididymitis, prostatitis
Note: 90% of infected men are asymptomatic but can transmit infection.
COMPLICATIONS
Untreated Disease
  • 2-3× increased HIV acquisition risk
  • Increased HIV viral shedding
  • Pelvic inflammatory disease (PID)
  • Preterm birth and low birth weight
  • Infertility (rare)
  • Facilitation of other STI transmission

Investigations

Diagnosis relies on laboratory testing as clinical presentation alone is insufficient. Point-of-care testing and molecular methods have largely replaced traditional wet mount microscopy due to superior sensitivity.

  • Essential
    Nucleic Acid Amplification Test (NAAT)
    Gold standard. Sensitivity 95-100%, specificity >99%. Available in most Australian pathology laboratories. Can use first-void urine (men), vaginal swab, or cervical swab (women). Results available within 24-48 hours.
  • Available
    Point-of-Care Antigen Tests
    OSOM® Trichomonas Rapid Test. Sensitivity 83-95% in symptomatic women, lower in asymptomatic. Results in 10 minutes. Useful in remote settings where NAAT unavailable. Not PBS funded.
  • Traditional
    Wet Mount Microscopy
    Sensitivity only 60-70%, specificity >99%. Requires immediate examination of fresh vaginal discharge. Mobile trichomonads with characteristic jerky motility. Not recommended as sole test due to poor sensitivity.
  • Alternative
    Culture
    InPouch TV culture system. Sensitivity 85-95%, specificity >99%. Useful for antimicrobial susceptibility testing in treatment failures. Results in 2-7 days. Available in reference laboratories.
  • Concurrent
    Comprehensive STI Screen
    Test for chlamydia, gonorrhea, syphilis, and HIV in all patients with trichomoniasis. High rates of co-infection, particularly in ATSI populations. Include hepatitis B testing if not previously screened.
  • Special Cases
    Antimicrobial Susceptibility Testing
    Indicated for treatment failures or recurrent infection within 3 months. Performed by reference laboratories (VIDRL Melbourne, ICPMR Sydney). Tests metronidazole and tinidazole susceptibility.
⚠️
Testing Considerations: In men, first-void urine NAAT is preferred over urethral swabs due to improved sensitivity and patient acceptability. Avoid urination for 2 hours prior to collection. In women, vaginal swabs (self-collected or clinician-collected) are preferred over cervical swabs.

Risk Stratification

Risk stratification guides screening frequency and contact tracing intensity. High-risk populations require enhanced case management and partner notification strategies.

HIGH RISK
Intensive Management
  • ATSI women in remote communities
  • Sex workers
  • Multiple sexual partners (>1 in past year)
  • History of recurrent STIs
  • HIV-positive individuals
  • Pregnant women with risk factors
Actions: 3-6 monthly screening, enhanced partner notification, directly observed therapy consideration
MODERATE RISK
Standard Management
  • New sexual partner in past 3 months
  • Partner with diagnosed STI
  • Inconsistent condom use
  • Age <25 years sexually active
  • Previous trichomoniasis infection
Actions: Annual screening if sexually active, standard partner notification
LOW RISK
Routine Care
  • Monogamous relationship >12 months
  • Consistent condom use
  • No STI history
  • Regular partner tested negative
Actions: Screening only if symptomatic or routine sexual health check every 2-3 years

Pregnancy Considerations

🚨
Pregnancy Alert: Trichomoniasis in pregnancy increases risk of preterm delivery, premature rupture of membranes, and low birth weight. Treatment is safe and recommended with metronidazole after first trimester. Screen all pregnant ATSI women and those with risk factors.
🤰 Pregnancy Management
Screening Universal screening for ATSI women, risk-based for others
First Trimester Defer treatment unless severe symptoms. Clotrimazole for symptom relief.
Second/Third Trimester Metronidazole 2g single dose or 400mg BD for 7 days (Category B2)
Partner Treatment Essential to prevent re-infection. Same regimen as non-pregnant patients.

Treatment of Trichomoniasis

First-Line Therapy

💊
Metronidazole
Flagyl® · Metronide® · First-line
Adult Dose 2 g single dose OR 400 mg twice daily for 7 days
Paediatric 15 mg/kg/day divided into 3 doses × 7 days (max 2 g/day)
Route Oral
Duration Single dose preferred OR 7 days
Renal Adj. No adjustment required
Hepatic Adj. Reduce dose by 50% in severe impairment
PBS Status ✓ PBS General Benefit
ℹ️
Single-dose preference: Single 2 g dose is preferred for improved compliance and equivalent efficacy. Seven-day regimen may be used if single dose not tolerated or in pregnancy.

Alternative Therapy

💊
Tinidazole
Fasigyn® · Alternative agent
Adult Dose 2 g single dose
Paediatric 50 mg/kg single dose (max 2 g)
Route Oral
Duration Single dose
Renal Adj. No adjustment required
Hepatic Adj. Reduce dose by 50% in severe impairment
PBS Status ⚠ PBS Authority Required

Treatment of Resistant Trichomoniasis

⚠️
Suspected resistance: Consider if symptoms persist 1 week after completion of standard therapy and re-infection has been ruled out.
💊
Metronidazole (High-dose)
Flagyl® · For resistant cases
Adult Dose 400 mg three times daily × 7 days
Alternative 2 g daily × 3-5 days
Route Oral
Monitoring Monitor for GI side effects
💊
Tinidazole (High-dose)
Fasigyn® · For resistant cases
Adult Dose 2 g daily × 5 days
Alternative 1 g twice daily × 5 days
Route Oral
Monitoring Monitor for neurological side effects

Partner Treatment

🚨
Mandatory partner treatment: All sexual partners from the past 4 weeks (or last partner if >4 weeks) must be treated simultaneously with the same regimen, regardless of symptoms or test results.
1
Identify Partners
Contact trace all sexual partners from 4 weeks prior to symptom onset or last partner if >4 weeks
2
Treat Partners
Same treatment regimen as index case - metronidazole 2 g single dose preferred
3
Sexual Abstinence
No sexual contact until both partners complete treatment and are asymptomatic for 7 days

Treatment Monitoring

Day 0
Treatment initiation: Start metronidazole. Counsel on alcohol avoidance and partner treatment.
Day 7
Treatment completion: Assess symptom resolution. Confirm partner treatment completed.
2-4 weeks
Follow-up visit: Test of cure recommended in pregnancy or if symptoms persist. Screen for other STIs.
3 months
Repeat screening: Consider re-screening due to high rates of re-infection, particularly in high-risk populations.

Treatment Failure Management

Approach to Treatment Failure
  • Confirm compliance with initial treatment regimen
  • Rule out re-infection by untreated or new partner
  • Consider higher-dose metronidazole: 400 mg TDS × 7 days
  • Alternative: Tinidazole 2 g daily × 5 days
  • If still failing: Specialist referral for resistance testing
  • Consider combination therapy under specialist guidance

Drug Interactions and Contraindications

⚠️
Alcohol interaction: Patients must avoid alcohol during treatment and for 48 hours after completion due to disulfiram-like reaction with metronidazole and tinidazole.
Major Interactions
  • Warfarin: Increased INR - monitor closely
  • Lithium: Increased lithium levels
  • Phenytoin: Reduced metronidazole efficacy
  • Alcohol: Disulfiram-like reaction
Contraindications
  • Known hypersensitivity to nitroimidazoles
  • First trimester pregnancy (relative contraindication)
  • Severe neurological disorders (for tinidazole)
  • Blood dyscrasias

References

  • 01
    Workowski KA, Bachmann LH, Chan PA, et al. Sexually transmitted infections treatment guidelines, 2021. MMWR Recomm Rep. 2021;70(4):1-187.
  • 02
    Kissinger P. Trichomonas vaginalis: a review of epidemiologic, clinical and treatment issues. BMC Infect Dis. 2015;15:307. doi:10.1186/s12879-015-1055-0
  • 03
    Australian STI Management Guidelines. Trichomoniasis. Sydney: Sexual Health Society of Victoria; 2022. Available at: http://www.sti.guidelines.org.au
  • 04
    Schwebke JR, Hobbs MM, Taylor SN, et al. Molecular testing for Trichomonas vaginalis in women: results from a prospective U.S. clinical trial. J Clin Microbiol. 2011;49(12):4106-4111.
  • 05
    Department of Health. National Notifiable Diseases Surveillance System Annual Report 2022. Canberra: Australian Government Department of Health; 2023.
  • 06
    Muzny CA, Schwebke JR. The clinical spectrum of Trichomonas vaginalis infection and challenges to management. Sex Transm Infect. 2013;89(6):423-425.
  • 07
    PBS Online. Metronidazole and tinidazole listings. Canberra: Australian Government Department of Health; 2024. Available at: https://www.pbs.gov.au
  • 08
    Silver BJ, Guy RJ, Kaldor JM, et al. Trichomonas vaginalis as a cause of perinatal morbidity: a systematic review and meta-analysis. Sex Transm Dis. 2014;41(6):369-376.
  • 09
    Australian Commission on Safety and Quality in Health Care. Antimicrobial Stewardship Clinical Care Standard. Sydney: ACSQHC; 2021.
  • 10
    Moodley P, Wilkinson D, Connolly C, et al. Trichomonas vaginalis is associated with pelvic inflammatory disease in women infected with human immunodeficiency virus. Clin Infect Dis. 2002;34(4):519-522.
  • 11
    RHDAustralia. Aboriginal and Torres Strait Islander STI Management Guidelines. Darwin: Menzies School of Health Research; 2023.
  • 12
    Sobel JD, Nagappan V, Nyirjesy P. Metronidazole-resistant vaginal trichomoniasis - an emerging problem. N Engl J Med. 1999;341(4):292-293.
  • 13
    Van Der Pol B, Williams JA, Orr DP, et al. Prevalence, incidence, natural history, and response to treatment of Trichomonas vaginalis infection among adolescent women. J Infect Dis. 2005;192(12):2039-2044.
  • 14
    Soper D. Trichomoniasis: under control or undercontrolled? Am J Obstet Gynecol. 2004;190(1):281-290.
  • 15
    Australian Institute of Health and Welfare. Australia's health 2022: in brief. Cat. no. AUS 240. Canberra: AIHW; 2022.