What is bacterial vaginosis and how is it acquired in women of reproductive age?

What is Bacterial Vaginosis?

Bacterial vaginosis is a vaginal dysbiosis syndrome—not a traditional infection—caused by the replacement of protective hydrogen peroxide-producing Lactobacillus species with an overgrowth of anaerobic bacteria including Prevotella, Mobiluncus, Gardnerella vaginalis, and Mycoplasma hominis. 1

Core Pathophysiology

• BV represents an ecological disruption rather than infection with a single pathogen—it's fundamentally a syndrome of vaginal dysbiosis where the normal protective bacterial environment collapses 1
• The loss of H₂O₂-producing Lactobacillus species allows anaerobic bacteria (Bacteroides, Mobiluncus, Prevotella bivia, Prevotella disiens, Porphyromonas, Peptostreptococcus) and Gardnerella vaginalis to proliferate 2, 1
• This microbial shift causes vaginal pH to rise from the normal 3.8-4.2 to above 4.5, which both results from and perpetuates the loss of Lactobacillus dominance 1

Clinical Presentation

• BV is the most prevalent cause of vaginal discharge and malodor in women of reproductive age 2, 3
• A critical pitfall: up to 50% of women meeting diagnostic criteria for BV are completely asymptomatic, meaning absence of symptoms does not exclude the diagnosis or eliminate complication risks 1, 3
• When symptomatic, women experience homogeneous white discharge that smoothly coats vaginal walls, characteristic fishy odor (especially after intercourse or with alkaline exposure), and minimal vulvar irritation 2, 3

How Do You Get Bacterial Vaginosis?

BV is strongly associated with sexual activity but is NOT classified as a sexually transmitted infection—it results from ecological disruption of the vaginal microbiome triggered by sexual and environmental factors, not acquisition of a single transmissible pathogen. 1, 4

Sexual and Behavioral Risk Factors

• Women who have never been sexually active are rarely affected by BV 2, 1
• Risk increases with multiple sexual partners, younger age at first intercourse, being unmarried, and commercial sex work 5
• However, treating male sexual partners does NOT prevent BV recurrence, which is the critical distinction from true STIs like gonorrhea or chlamydia where partner treatment is essential 2, 3, 4
• The CDC explicitly states "it is unclear whether BV results from acquisition of a sexually transmitted pathogen" despite the strong epidemiological associations with sexual behavior 4

Environmental and Chemical Triggers

• Vaginal douching and use of chemical irritants (regular soap, vaginal products) disrupt the protective vaginal ecosystem and can trigger the microbial shift toward BV 1
• The rectum may serve as a reservoir for some BV-associated flora, similar to the pathogenesis of urinary tract infections 6

Why the Confusion About Transmission?

• BV appears in STI treatment guidelines because it's frequently diagnosed during STI evaluations, NOT because it's sexually transmitted 4
• Six randomized trials demonstrated no benefit from routine partner treatment in preventing recurrence 4
• In clinical practice, do not automatically treat partners as you would for true STDs—this represents unnecessary antibiotic exposure without proven benefit 4

Clinical Significance Beyond Symptoms

• BV creates conditions that significantly increase risk of pelvic inflammatory disease, endometritis, post-abortion infections, vaginal cuff cellulitis, preterm birth, and increased susceptibility to HIV, HSV-2, Chlamydia, and gonorrhea 1, 3, 5
• Women with BV have 1.8-fold increased risk for gonorrhea and 1.9-fold increased risk for Chlamydia infection 5
• The CDC recommends considering treatment of even asymptomatic BV before surgical abortion procedures specifically because of elevated infection risk 1