Bacterial vaginosis

Cause

A clinical syndrome characterised by a loss of vaginal Lactobacilli, and increased numbers of diverse anaerobic bacteria including Gardnerella vaginalis, Atopobium vaginae, Mobiluncus spp, Prevotella spp and other bacterial vaginosis (BV)-associated bacteria.
This change is accompanied by a rise in vaginal pH and increased amines which can produce an odour.
The sequence of events leading to the shift in the vaginal microbiome is unclear

Most common cause of abnormal vaginal discharge in people of childbearing age
Up to 50% of people are asymptomatic
While BV is not currently considered to be a sexually transmitted infection (STI), there is strong observational evidence supporting the contribution of sexual transmission to its pathogenesis
Risk factors include:
- Sexual partner change (or sex with the same partner for recurrent BV)
- Vaginal douching
- Presence of an intrauterine device (IUD)
Hormonal contraception appears to be protective regardless of type. Condom use or having a male partner who is circumcised is also protective
Recurrence is common

Signs and symptoms

Approximately 50% of people are asymptomatic

Thin white homogenous vaginal discharge without obvious vaginal inflammation

Offensive fishy odour

Complications

Although BV may be associated with a number of adverse health outcomes, routine screening and treatment has not been conclusively shown to reduce the risk.

Spontaneous abortion, premature labour, chorioamnionitis, postpartum endometritis
Pelvic inflammatory disease (PID)
Endometritis, post termination of pregnancy or IUD insertion
Often associated with STIs including chlamydia, gonorrhoea and trichomoniasis
HIV transmission and acquisition

All people complaining of vaginal discharge should be examined to identify relevant clinical signs, and to exclude a retained foreign body (e.g. tampon or condom) as a cause of the discharge
Self-collected swabs can be obtained if examination is declined, but this is not recommended
Trichomoniasis, chlamydia and gonorrhoea are other possible causes of vaginal discharge. Unless STIs have been excluded, testing should occur as part of a full sexual health check

Test	Consideration
High vaginal swab for Candida and BV	Clinical details must be included on laboratory form to ensure sample is processed appropriately Candidiasis is another common cause of unusual vaginal discharge
Consider:
Vulvovaginal NAAT swab for chlamydia, gonorrhoea and trichomoniasis	If examined, vaginal swab should be taken before speculum insertion Trichomoniasis, chlamydia and gonorrhoea are other possible causes of unusual vaginal discharge and should be excluded
HIV and syphilis serology	If STI screening is indicated

NAAT – Nucleic Acid Amplification Test

Treatment is predominantly aimed at alleviating symptoms and is indicated in symptomatic people

The benefits of treatment are inconclusive for the following people. Refer to local protocols:
- Asymptomatic people undergoing an invasive upper genital tract procedure e.g. termination of pregnancy or IUD insertion
- Asymptomatic pregnant people with a history of previous pre-term delivery

Recommendation

Alternative

Metronidazole 400 mg orally with food, twice daily for 7 days

Metronidazole 2 g orally, as a single dose (less effective than 7 day course)

Ornidazole 500 mg orally, twice daily for 5 days (avoid in pregnancy)

Clindamycin 300 mg orally, twice daily for 7 days

Special Situations

Situation	Recommendation
Breastfeeding	Metronidazole may affect taste of breast milk; avoid high doses in breastfeeding Current recommended dose of metronidazole 400 mg orally, twice daily for 7 days is safe in breastfeeding
Pregnancy	Metronidazole 400mg orally with food, twice daily for 7 days Symptomatic pregnant people should be treated Treatment of asymptomatic pregnant people has not been shown to improve pregnancy outcomes Treatment of pregnant people with BV who have a history of previous pre-term delivery MAY reduce the risk of a further pre-term delivery but the evidence is inconclusive – refer to local protocols
Allergy or contraindications	If allergic or intolerant to nitroimidazoles, use clindamycin 300 mg orally, twice daily for 7 days or seek specialist advice.
Post-menopausal women	Menopause alters the vaginal microbiome, which affects the validity of laboratory diagnostic criteria for BV. Symptoms may be related to atrophic vaginitis. Consider the use of topical oestrogen

If a patient has an IUD leave it in place and treat as recommended. Seek specialist advice as needed
Single dose and short duration regimens are associated with higher rates of recurrence
Recurrence is common. Seek specialist advice if more than 3 recurrences in a 12-month period