BASHH Guidelines

Home Back


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


Presence of an STI e.g. chlamydia or herpes

Clinical Features

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:


1) 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.


2) 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