References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Gardnerella vaginalis is a bacterium commonly associated with bacterial vaginosis (BV), the most common vaginal infection in women of childbearing age. It’s not technically an STI, though sexual activity can trigger it. BV occurs when gardnerella and other anaerobic bacteria overgrow, disrupting the normal vaginal flora.
If you’ve been told you have gardnerella or are experiencing symptoms of BV, this guide covers what it means, how it’s tested, and how to treat it.
Get tested for BV and STIs with a home test kit
What Is Gardnerella?
Gardnerella vaginalis is a bacterium that naturally lives in the vagina in small numbers. It only causes problems when it overgrows, usually alongside other anaerobic bacteria, creating the condition known as bacterial vaginosis.
BV is not caused by poor hygiene. It’s a bacterial imbalance. Triggers include new sexual partners, douching, and use of scented products in the vaginal area.
Symptoms
- Thin, greyish-white vaginal discharge
- Strong fishy smell, particularly after sex or during periods
- Itching or irritation (less common than with thrush)
- No redness or swelling (unlike thrush)
Around 50% of women with BV have no symptoms at all. It’s often discovered incidentally during routine screening.
How Is Gardnerella/BV Tested?
- Vaginal swab: A self-collected or clinician-collected swab tested in a lab
- pH testing: BV raises vaginal pH above 4.5 (normal is 3.8-4.5)
- Whiff test: Adding potassium hydroxide to the sample releases a fishy odour
- Microscopy: Examining the swab under a microscope shows “clue cells” (vaginal cells coated in bacteria)
BV testing is available at sexual health clinics, through your GP, or with some home test kits.
Treatment
- Metronidazole 400mg twice daily for 5-7 days (first-line)
- Fluomizin vaginal tablets for 6 nights (no alcohol restriction)
- Metronidazole gel applied vaginally for 5 nights (alternative)
BV has a recurrence rate of around 50% within 12 months. If it keeps coming back, your doctor may recommend a longer treatment course or maintenance therapy.
Frequently Asked Questions
Is gardnerella an STI?
No. BV is not classified as an STI, though sexual activity can trigger it. It’s caused by an imbalance in vaginal bacteria, not by a sexually transmitted organism. Male partners do not need treatment.
Can gardnerella affect pregnancy?
Yes. BV during pregnancy is associated with premature birth and low birth weight. Pregnant women with symptoms should be tested and treated. Fluomizin is considered safe in pregnancy.
Why does BV keep coming back?
The exact reason for BV recurrence is not fully understood. Triggers include new sexual partners, unprotected sex, douching, and use of scented products. Maintaining vaginal health with probiotics and avoiding irritants may help, though evidence is limited.
Related reading
- Can You Test for STIs While on Your Period?
- Common STI Symptoms in Women
- How Different STIs Affect Vaginal Discharge
- Is Testicular Pain a Sign of an STI?
- What Are Vaginal Bumps? Causes and When to Worry
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
