Skip to main content

Bacterial Vaginosis 2012


Bacterial vaginosis (BV) is the commonest cause of abnormal discharge in women of childbearing age.

The reported prevalence has varied from 5% in a group of asymptomatic college students to as high as 50% of women in rural Uganda. A prevalence of 12% was found in pregnant women attending an antenatal clinic in the United Kingdom, and of 30% in women undergoing termination of pregnancy.

Lactobacilli are the dominant bacteria in the healthy vagina. The pH is maintained below 4.5, and there are low levels of other bacteria. In BV the pH of vaginal fluid is elevated above 4.5 and up to 6.0. Lactobacilli may be present, but the flora is dominated by many anaerobic and facultative anaerobic bacteria, with concentrations up to a thousand-fold greater than normal. Conventional culture techniques identified Gardnerella vaginalis, Prevotella spp., Mycoplasma hominis, and Mobiluncus spp. as those most commonly found. Recent studies using molecular techniques have identified many other species including Atopobium vaginalis, Clostridiales spp. (BV 1-3), Leptotrichia spp., Sneathia spp. A biofilm consisting mainly of Gardnerella and Atopobium has been described more recently, implicating these two species as critical in the aetiology. There is debate about whether BV is merely an imbalance in vaginal ecology, or is initiated as a sexually transmitted infection (STI).

Risk factors include:

  • Vaginal douching
  • Receptive cunnilingus
  • Black race
  • Recent change of sex partner
  • Smoking
  • Presence of an STI e.g. chlamydia or herpes


Clinical Features


  • Offensive fishy smelling vaginal discharge
  • Not associated with soreness, itching, or irritation
  • Many women (approximately 50%) are asymptomatic


  • Thin, white, homogeneous discharge, coating the walls of the vagina and vestibule.


BV is not usually associated with signs of inflammation.



Two approaches are available:

Gram stained vaginal smear, evaluated with the Hay/Ison criteria (recommended by Bacterial Special Interest group of BASHH) (C) or the Nugent criteria

The Hay/Ison criteria are defined as follows:

  • grade 1 (Normal): Lactobacillus morphotypes predominate.
  • grade 2 (Intermediate): Mixed flora with some Lactobacilli present, but Gardnerella or Mobiluncus morphotypes also present
  • grade 3 (BV): Predominantly Gardnerella and/or Mobiluncus morphotypes. Few or absent Lactobacilli.

There are additional grades which have not been correlated with clinical features:

  • grade 0: No bacteria present
  • grade 4: Grampositive cocci predominate.

Amsel’s criteria

At least three of the four criteria are present for the diagnosis to be confirmed.

  1. Thin, white, homogeneous discharge
  2. Clue cells on microscopy of wet mount
  3. pH of vaginal fluid >4.5
  4. Release of a fishy odour on adding alkali (10% KOH)



General advice

Patients should be advised to avoid vaginal douching, use of shower gel, and use of antiseptic agents or shampoo in the bath (grade of recommendation C).

Treatment is indicated for:

  • Symptomatic women (A)
  • Women undergoing some surgical procedures (A)
  • Women who do not volunteer symptoms may elect to take treatment if offered

They may report a beneficial change in their discharge following treatment.(C)

Recommended regimens

Metronidazole 400mg twice

  • daily for 5-7 days (A)

  • Metronidazole 2 g single dose (A).

  • Intravaginal metronidazole gel (0.75%) once daily for 5 days (A)

  • Intravaginal clindamycin cream (2%) once daily for 7 days (A)

Alternative regimens

  • Tinidazole 2G single dose (A).

  • Clindamycin 300 mg twice daily for 7 days (A).


Caution - avoid alcohol with both oral and topical metronidazole.



Pregnancy and breast feeding

Symptomatic pregnant women should be treated in the usual way (B).

There is insufficient evidence to recommend routine treatment of asymptomatic pregnant women who attend a GU clinic and are found to have BV.

Women with additional risk factors for preterm birth may benefit from treatment before 20 week gestation.


Follow up

A test of cure is not required if symptoms resolve.


For recurrent bacterial vaginitis see full guideline.


Download the Full Guidelines

BV 2012