Is BVAB 2,3 Contagious?
Bacterial vaginosis-associated bacteria (BVAB), including BVAB-2 and BVAB-3, are not considered classically contagious in the traditional sense of sexually transmitted infections, though sexual activity clearly facilitates bacterial exchange between partners. 1
The Nuanced Reality of BV Transmission
The CDC explicitly states that "bacterial vaginosis is not usually transmitted sexually," despite strong epidemiological associations with sexual behavior 1. This seemingly contradictory position reflects the complex nature of BV:
BV represents an ecological disruption rather than infection with a single transmissible pathogen—it's a syndrome of vaginal dysbiosis where normal H₂O₂-producing Lactobacillus species are replaced by high concentrations of anaerobic bacteria including BVAB-2, BVAB-3, Gardnerella vaginalis, Prevotella species, and Mycoplasma hominis 2
The mechanism remains incompletely understood—the CDC acknowledges "it is unclear whether BV results from acquisition of a sexually transmitted pathogen" 1
Women who have never been sexually active are rarely affected, and BV is strongly associated with having multiple sex partners, suggesting sexual activity plays a facilitating role 3, 2
Evidence Against Traditional "Contagion" Model
The most compelling evidence that BVAB are not contagious in the classic STI sense comes from treatment trials: six randomized controlled trials showed that treating male sex partners provides no benefit in preventing BV recurrence in women 1. This is a critical distinction from true sexually transmitted infections like gonorrhea or chlamydia, where partner treatment is essential 1.
The ACOG reinforces that "treatment of male sex partners has not been beneficial in preventing BV recurrence" 1
This failure of partner treatment has historically eroded confidence in the sexual transmission hypothesis 4
The Sexual Exchange Paradox
Despite the lack of benefit from partner treatment, there is robust molecular and epidemiological evidence supporting bacterial exchange between partners during sexual activity 4:
Recent research demonstrates that bacteria can be exchanged between partners, though this doesn't necessarily translate to clinical reinfection causing recurrent BV 4
The pathogenesis of BV recurrence is likely multifaceted—not attributable to reinfection alone but also to persistence of BVAB or biofilms following antimicrobial therapy 4
Clinical Practice Implications
When counseling patients, emphasize that while BV is not a classic STD requiring partner notification and treatment, sexual activity does influence its development and recurrence 1:
Do not automatically treat partners as you would for true STDs—this represents unnecessary antibiotic exposure without proven benefit 1
Focus instead on treating the affected woman and addressing other risk factors like douching, which disrupts the protective vaginal ecosystem 2
Women with underlying conditions like uncontrolled diabetes or those on corticosteroids may not respond as well to standard therapies 2
The Recurrence Challenge
BV has an unacceptably high recurrence rate of approximately 80% within three months after effective treatment, highlighting that our current treatment paradigm (antibiotics to women alone) is insufficient 5, 4
Up to 50% of women with BV are completely asymptomatic, meaning absence of symptoms doesn't eliminate risk of complications 2