What causes bacterial vaginosis?

Causes of Bacterial Vaginosis

Bacterial vaginosis (BV) is caused by a disruption of the normal vaginal flora, characterized by a shift from predominantly Lactobacillus species to an overgrowth of anaerobic bacteria, particularly Gardnerella vaginalis and other anaerobic organisms. 1, 2

Pathophysiology of Bacterial Vaginosis

BV represents a complex ecological disturbance in the vaginal microbiome:

• Normal vaginal flora disruption: The healthy vagina is typically dominated by aerobic Lactobacillus species, which are replaced by anaerobic bacteria in BV 1, 3
• pH changes: BV is associated with an elevated vaginal pH (>4.5), compared to the normal acidic environment (≤4.5) maintained by Lactobacilli 1
• Bacterial overgrowth: There is a significant increase in anaerobic bacteria, with Gardnerella vaginalis being a predominant organism 3

Risk Factors and Contributing Causes

Several factors have been associated with the development of BV:

Behavioral Factors

• Sexual activity: While sexual transmission has not been definitively proven, BV is more common in sexually active women 4
• Smoking: Tobacco use has been identified as a risk factor for BV development 2
• Hygiene practices: Certain vaginal douching practices may disrupt normal flora 2

Physiological Factors

• Hormonal changes: Fluctuations in hormones during menstrual cycle can affect vaginal environment 2
• Use of certain contraceptives: Some contraceptive methods may influence BV risk 2

Microbial Factors

• Biofilm formation: Gardnerella vaginalis and other bacteria can form biofilms that are resistant to treatment 2
• Lactobacilli depletion: Reduction in protective Lactobacillus species, particularly L. crispatus 2

Clinical Significance

Understanding the causes of BV is important due to its associated complications:

• Gynecological complications: Increased risk of pelvic inflammatory disease, postoperative infections, and cervicitis 5
• Obstetric risks: Higher rates of preterm birth, premature rupture of membranes, and postpartum endometritis 1, 5
• STI susceptibility: BV increases susceptibility to sexually transmitted infections, including HIV 6, 5

Recurrence Patterns

BV has a high recurrence rate, which suggests persistent underlying causes:

• Treatment failure: 50-80% of women experience BV recurrence within one year after antibiotic treatment 2
• Incomplete restoration of normal flora: After treatment, beneficial Lactobacillus strains often fail to recolonize the vagina 2
• Biofilm persistence: Bacterial biofilms may persist despite antibiotic therapy 2

Diagnostic Considerations

The CDC and American Academy of Family Physicians recommend diagnosing BV based on:

• Clinical criteria: Presence of thin, homogeneous discharge with fishy odor 1
• Laboratory findings: Vaginal pH >4.5, positive whiff test, and presence of "clue cells" on microscopy 1

Prevention Strategies

Based on the understanding of BV causes, several preventive approaches may be considered:

• Behavioral modifications: Smoking cessation, consistent condom use 2
• Probiotics: Supplementation to restore beneficial Lactobacillus species 1, 2
• pH modulation: Maintaining normal vaginal acidity 2
• Biofilm disruption: Strategies to prevent or disrupt bacterial biofilms 2

It's important to note that while BV is often symptomatic (causing discharge and odor), more than half of women with BV may be asymptomatic 4, highlighting the importance of regular gynecological screening.