Is Bacterial Vaginosis Sexually Transmitted?

Bacterial vaginosis is not a classic sexually transmitted infection, though it is clearly associated with sexual activity and behaviors. 1

The Paradox of BV and Sexual Activity

BV occupies a unique position that distinguishes it from traditional STIs:

Women who have never been sexually active rarely develop BV, establishing a clear link between sexual behavior and disease occurrence 2, 1
However, BV does not behave like a typical STI because treating male sexual partners has consistently failed to prevent recurrence in women across multiple decades of CDC guidelines 2, 1
Male partners are not symptomatic, and their treatment does not alter the clinical course or reduce relapse rates in affected women 1

The Centers for Disease Control and Prevention has maintained a consistent stance across multiple guideline iterations:

BV is associated with having multiple sex partners, but it remains unclear whether this results from acquisition of a sexually transmitted pathogen 2
The CDC explicitly recommends against routinely treating male partners of women with BV 1
BV results from replacement of normal H₂O₂-producing Lactobacillus species with high concentrations of anaerobic bacteria, G. vaginalis, and Mycoplasma hominis 2, 3

The relationship between BV and sexual activity is more nuanced than simple transmission:

BV is associated with indicators of high-risk sexual behavior including new sexual partners, greater number of partners, and increased lifetime sexual partners 4
BV is common among women-who-have-sex-with-women, relating at least in part to non-coital sexual behaviors 5
Non-penetrative sexual contact (digito-genital contact, oral sex) also enhances BV risk, indicating that sex per se—but not necessarily coital transmission—is involved 5
Frequency of intercourse appears to be a critical factor, possibly through mechanical transfer of perineal enteric bacteria or alkalinization of the vaginal environment 5

Rather than a sexually transmitted infection, BV may be better conceptualized as a "sexually enhanced disease" (SED) 5:

Sexual activity may mechanically transfer perineal enteric bacteria into the vagina 5
Unprotected intercourse causes alkalinization of the vaginal environment, enhancing the shift from lactobacilli-dominated flora to BV-associated flora 5
Condom use is slightly protective, supporting the mechanical and pH-related mechanisms rather than pathogen transmission 5

The primary treatment goal is to relieve vaginal symptoms in the affected woman, not to treat partners 1:

Up to 50% of women with BV are asymptomatic 3, 1
BV has a high recurrence rate (50-80% within one year) regardless of partner treatment 3, 1
Treatment focuses on metronidazole 500 mg orally twice daily for 7 days or alternative regimens 6, 3

BV rarely occurs in prepubertal girls and postmenopausal women, suggesting hormonal components in its etiology 7
The reservoir for BV-associated organisms is probably the distal intestinal tract and mouth, not sexual partners 7
G. vaginalis carriage has been observed among adolescent, sexually non-experienced girls, contradicting that sexual transmission is a necessary prerequisite 5