How Bacterial Vaginosis is Contracted
Bacterial vaginosis is not "contracted" in the traditional sense of an infection—it develops from an internal disruption of the normal vaginal ecosystem where healthy Lactobacillus bacteria are replaced by an overgrowth of anaerobic bacteria, Gardnerella vaginalis, and Mycoplasma hominis. 1, 2
Understanding the Mechanism
BV results from replacement of normal H₂O₂-producing Lactobacillus species in the vagina with high concentrations of anaerobic bacteria (including Prevotella species and Mobiluncus species), rather than acquisition of a single pathogen from an external source. 1, 2
The exact cause of this microbial alteration remains unclear, though it represents a shift in the vaginal ecology rather than transmission of a specific infectious agent. 1
Risk Factors for Development
Sexual activity is strongly associated with BV development:
- Having multiple sexual partners significantly increases risk 1, 3
- New sexual partners also elevate risk 3
- Women who have never been sexually active are rarely affected, suggesting sexual activity plays a role even though the exact mechanism is unclear 1, 2, 3
However, it is unclear whether BV results from acquisition of a sexually transmitted pathogen or from other mechanisms related to sexual activity. 1, 2
Other risk factors include:
- Douching 1
- Lack of vaginal lactobacilli 1
- African-American ethnicity 3
- Low socioeconomic status 3
- Previous history of preterm birth 3
Critical Clinical Pitfall
Treatment of male sexual partners has NOT been shown to prevent recurrence of BV, which further supports that BV is not a straightforward sexually transmitted infection. 1, 2, 3 This is a common misconception that leads to unnecessary partner treatment.
The Rectal Reservoir Theory
Some evidence suggests the pathogenesis may be similar to urinary tract infections, with the rectum potentially serving as a reservoir for BV-associated flora, though this mechanism is not fully established. 4
Key Distinction from STIs
Unlike traditional sexually transmitted infections where a pathogen is passed from one person to another, BV represents an ecological imbalance of organisms that are often already present in the vaginal environment as part of the endogenous flora. 4 The condition involves overgrowth of bacteria that may already exist in small numbers rather than introduction of entirely new pathogens.