Bacterial Vaginosis

Bacterial vaginosis is a polymicrobial dysbiosis of the vaginal flora, not a sexually transmitted infection in the classic sense, though it is associated with sexual activity.

Normal lactobacillus dominant flora, which maintains an acidic vaginal pH, is replaced by an overgrowth of anaerobic organisms, principally Gardnerella vaginalis, alongside Prevotella, Mobiluncus, and Atopobium vaginae species.

It is the most common cause of abnormal vaginal discharge in women of reproductive age.

A thin, grey-white, homogeneous discharge with a characteristic fishy odor, classically more noticeable after intercourse or during menstruation (both raise vaginal pH, favoring anaerobic overgrowth).

Itching and inflammation are notably absent or minimal, distinguishing it clinically from candidiasis and trichomoniasis.

Up to half of affected women are asymptomatic.

• Amsel's criteria (clinical diagnosis, 3 of 4 required): homogeneous thin discharge, vaginal pH above 4.5, positive whiff test (fishy odor on adding 10% KOH to a sample), and clue cells (epithelial cells studded with adherent bacteria) on microscopy
• Gram stain with Nugent scoring is the laboratory gold standard where available
• NAAT based testing is increasingly used in some settings

• Metronidazole 400 to 500 mg PO bd for 5 to 7 days, or metronidazole 2 g PO as a single dose (lower cure rate than the multi-day course, reserved for adherence concerns), or metronidazole 0.75% vaginal gel, one applicator (5 g) intravaginally od for 5 days
• Alternative: clindamycin 2% vaginal cream, one applicator (5 g) intravaginally nocte for 7 days, or clindamycin 300 mg PO bd for 7 days
• Avoid alcohol during and for 48 hours after oral metronidazole given a disulfiram-like reaction
• Treatment in pregnancy is recommended for symptomatic women (oral metronidazole is considered safe at any gestation despite historical caution); asymptomatic BV in pregnancy is associated with preterm birth, but routine screening and treatment of asymptomatic women has not shown consistent benefit in reducing this risk
• Partner treatment is not recommended, given BV is not established as sexually transmitted in the conventional sense and partner treatment does not reduce recurrence
• Recurrent BV (frequent in practice) is managed with a repeat standard course, followed by consideration of suppressive therapy (metronidazole gel twice weekly for 3 to 6 months) in women with frequent recurrence; probiotic and boric acid adjuncts have some supporting evidence but are not universally recommended first line

Referral: gynecology for recurrent, refractory BV despite standard and suppressive therapy.