Part of the TeachMe Series

Bacterial Vaginosis

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Original Author(s): Grace Fitzgerald
Last updated: 13th February 2017
Revisions: 10

Original Author(s): Grace Fitzgerald
Last updated: 13th February 2017
Revisions: 10

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Bacterial vaginosis (BV) is a non-sexually transmitted infection of the lower genital tract in females, which occurs due to a disturbance in the normal vaginal flora, and a subsequent increase in vaginal pH. BV is a common condition, and is the most common cause of abnormal vaginal discharge in women of childbearing age.

In this article we will be looking at the pathophysiology, clinical features and management of Bacterial vaginosis.


In BV, the normal vaginal flora is disturbed, leading to a reduction in the numbers of lactobacilli bacteria in the vagina. Lactobacilli are large rod-shaped organisms that produce hydrogen peroxide to help maintain the acidic pH of the vagina <4.5 hence inhibiting the growth of other microorganisms.

When lactobacilli populations are reduced, the pH rises, allowing growth of other microorganisms. The infection is often polymicrobial, but the most common organisms found are Gardnerella vaginalis, anaerobes and mycoplasmas.

Risk Factors

Many risk factors for BV are those associated with a change in the normal vaginal flora:

  • Sexual activity – particularly a new partner or multiple sexual partners
  • The use of a contraceptive intrauterine device (IUD)
  • Receptive oral sex
  • Presence of an STI
  • Vaginal douching, or the use of scented soaps/vaginal deodorant
  • Recent antibiotic use
  • Ethnicity – more common in black women
  • Smoking

Clinical Features

Signs and symptoms are elicited from medical and sexual history and gynaecological examination.

Whilst up to 50% of case are asymptomatic, symptoms can include:

  • Offensive fishy smelling vaginal discharge
    • Not usually associated with soreness, itching or irritation

Signs on examination:

  • Thin, white/grey, homogenous vaginal discharge

Differential Diagnoses

Alongside BV, there are many other potential causes of abnormal vaginal discharge that must be considered. These include:

  • Vaginal Candidiasis – profuse thick white, itchy curd-like discharge
  • Trichomonas vaginalis – thin, frothy, offensive discharge, with associated irritation, dysuria and vaginal inflammation
  • STIs (gonorrhoea/chlamydia)


Diagnosis of BV relies on history, vaginal examination and microscopic examination.

Clue cells typical of Bacterial vaginosis infection

Clue cells typical of Bacterial vaginosis infection

Microscopy is the preferred method for diagnosis whereby a high vaginal smear (HVS) is gram stained and evaluated for:

  • The presence of ‘clue cells’ – vaginal epithelial cells studded with Gram variable coccobacilli
  • Reduced numbers of lactobacilli
  • Absence of pus cells

Note – the isolation of G. vaginalis is not sufficient to diagnose BV, as it can be cultured from the vagina of more than 50% of uninfected women.

Most clinics rely on microscopy however diagnosis can also be made based on a vaginal pH >4.5, and the KOH whiff test – whereby the addition of alkali (KOH) to the vaginal discharge causes release of a strong fishy odour (rarely done in practice).


Asymptomatic women may opt not to take any treatment. BV is treated with antibiotics, most commonly Metronidazole. This can be taken orally (400mg twice daily for 5-7 days, or a single dose of 2g) or as a gel applied directly to the vagina.  Regimens of Clindamycin or Tinidazole can also be used.

After diagnosis, the patient should also be advised to avoid vaginal douching, scented shower gels, antiseptic agents and shampoos in the bath. Removal of an IUD that may be contributing to the BV should also be considered.

Symptoms usually resolve with treatment, and so a follow up test of cure is not necessary. However, recurrent BV can occur, with more than half of successfully treated women finding that symptoms have returned, usually within three months.

Full details regarding the management of BV can be found in the BASHH guidelines.

Bacterial Vaginosis in Pregnancy

Untreated symptomatic BV can increase the risk of pregnancy-related complications such as premature birth, miscarriage and chorioamnionitis. Pregnant women experiencing symptoms of BV should contact their GP or GUM clinic. Treatment is the same as for non-pregnant women however if receiving treatment following birth, lactating women are advised to be treated with lower doses of metronidazole which can affect the taste of the breast milk.