Gardnerella vaginalis Transmission : BV Cause or STI?

Transmission of Gardnerella vaginalis : What You Need to Know

The transmission of the bacterium Gardnerella vaginalis is a topic surrounded by myths and misconceptions, often causing unnecessary worry. Many people mistakenly believe it is a sexually transmitted infection (STI) that you "catch" and pass on like chlamydia or gonorrhea. The reality, backed by current medical science, is far more nuanced. This article clarifies how Gardnerella vaginalis is spread, its direct link to Bacterial Vaginosis (BV).

What is Gardnerella vaginalis and Its Link to BV?

First, it's crucial to understand that Gardnerella vaginalis is not an STI¹. It is an anaerobic bacterium that is a natural part of the vaginal microbiome in many women. A healthy vagina maintains a delicate balance, predominantly of beneficial Lactobacillus bacteria, which keep the environment acidic and stable.

Bacterial Vaginosis (BV) occurs when this balance is disrupted. It is a polymicrobial dysbiosis, meaning there is an overgrowth of various anaerobic bacteria, including G. vaginalis, and a corresponding decrease in protective lactobacilli². Think of G. vaginalis not as an invading germ, but as a resident organism that can overgrow when the local environment changes.

Gardnerella vaginalis: Presence vs. Infection

It's common to have G. vaginalis present without any problems. The table below clarifies the distinction between simple presence and an active BV infection:

Aspect	Gardnerella vaginalis Presence	Bacterial Vaginosis (BV) Infection
Definition	The bacterium is part of the normal vaginal flora.	A clinical condition of microbial imbalance (dysbiosis).
Symptoms	None. It is an asymptomatic colonizer.	Can cause thin gray/white discharge, a strong fishy odor (especially after sex), and sometimes itching.
Diagnosis	Detected via specific lab tests (e.g., PCR).	Diagnosed clinically using Amsel Criteria (e.g., pH>4.5, clue cells, fishy odor).
Treatment Needed?	Normally No. Treatment is not required for asymptomatic colonization³.	Yes. Antibiotics like metronidazole or clindamycin are recommended to relieve symptoms and reduce risks.

How is Gardnerella vaginalis Transmitted?

Transmission is best understood not as catching a single bug, but as activities that can disrupt the vaginal ecosystem, allowing resident bacteria like G. vaginalis to overgrow. BV is therefore described by some researchers as a "sexually enhanced disease" rather than a classic STI⁴.

The primary transmission pathways are:

Sexual Activity (Heterosexual and Female-to-Female): While not an STI, sexual activity is a major risk factor for developing BV.
- Heterosexual Contact: Intercourse can mechanically introduce new bacteria and alter the vaginal pH, facilitating dysbiosis. Studies show high concordance of G. vaginalis strains between heterosexual partners⁴, and the bacteria can be found on the male penis and urethra.
- Female-to-Female Transmission: BV is more common among women who have sex with women (WSW). Sharing of vaginal fluids through sexual contact can transfer the disrupted microbial community.
Non-Sexual Transmission and Other Factors: BV can occur in individuals who are not sexually active, proving that sexual transmission of a single pathogen is not the sole cause.

Douching: This is a strongly discouraged practice that physically washes away protective lactobacilli, severely disrupting the vaginal flora and significantly increasing BV risk.
Other Risk Factors: Having multiple or new sexual partners, lack of condom use, and smoking are also associated with higher BV risk.

Crucial Update on Partner Treatment: For decades, treating male partners was not recommended. However, a landmark 2025 study published in the New England Journal of Medicine found that treating male partners with a combination of oral and topical antibiotics reduced BV recurrence in women from 63% to 35%⁵. This provides the strongest evidence to date that BV-associated bacteria can be sexually transmitted and highlights the importance of partner management in recurrent cases.

Prevention and Risk Reduction in Hong Kong

Prevention focuses on maintaining a healthy vaginal environment and reducing disruptive exposures:

Avoid Douching: The vagina is self-cleaning. Douching is harmful and increases BV risk.
Practice Safer Sex: Using condoms consistently can help protect the vaginal microbiome.
Consider Partner Treatment for Recurrent BV: If you suffer from frequent BV recurrences, discuss the latest evidence on partner treatment with your doctor.
Make Informed Lifestyle Choices: Limiting your number of sexual partners and not smoking may also help reduce risk.

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