Bacterial vaginosis


This is a condition caused by a change in vaginal bacterial flora from predominantly Lactobacilli species to various bacteria including Gardnerella vaginalis, Mobiluncus spp, Bacteroides spp, other anaerobes, and Mycoplasma hominis.

The incubation period is unknown.

Clinical presentation

This condition is not traditionally considered as an STI, although it is often associated with sexual activity. It presents as a smelly, 'fishy' discharge that is grey in colour. It is not an inflammatory condition, so the vagina is not usually red and inflamed. However, it can be associated with other inflammatory conditions such as candidiasis. The smell is often more noticeable after sex or at menstruation. Vulval irritation is usually mild, if present. However, many women with bacterial vaginosis have no symptoms.

This condition has been associated with:

  • premature labour
  • chorioamnionitis
  • PID especially after:
    • termination of pregnancy
    • intra-uterine device (IUD) insertion or other instrumentation.
  • increased risk of HIV transmission/acquisition
  • non-specific urethritis (NSU) in male partners.

Bacterial vaginosis can be diagnosed if three of the following four criteria are met:

  • raised vaginal pH >4.5
  • 'fishy' odour
  • characteristic discharge
  • presence of clue cells.

Thus, the diagnosis can be made at the examination and confirmed by a Gram stain smear from a high vaginal swab. Culture for the causative organisms is not performed routinely.


Symptomatic cases should be treated. Treatment is not required for asymptomatic disease, as this condition can often resolve spontaneously, but is recommended before gynaecological procedures and considered in pregnant women with a history of preterm labour.

Standard/initial therapy

  • Metronidazole 400 mg orally, 12-hourly with food for 5 days
  • Metronidazole 2 g orally, as a single dose (less effective)
  • Metronidazole gel 0.75 per cent gel 5 g, nocte for 5 nights (not on PBS)
  • Tinidazole 2 g orally, as a single dose with food
  • Clindamycin 2 per cent vaginal cream 5 g, daily for 7 days (not on PBS)
  • Clindamycin 300 mg orally, 12-hourly for 7 days (not on PBS).

Advise avoidance of alcohol with either metronidazole or tinidazole treatment and for 24 hours thereafter. Clindamycin cream is oil-based and may weaken latex condoms and diaphragms.

Recurrent disease

Single dose therapy is not recommended.


  • Clindamycin 300 mg orally, 12-hourly for 7 days (category A)
  • metronidazole 400 mg orally, 12-hourly for 5 days (category B2). Metronidazole can be used in the first trimester of pregnancy where the benefits outweigh the potential risks.
  • Medicines in pregnancy.

Systemic treatment is better in pregnancy and as clindamycin cream may not treat the upper genital tract adequately, oral therapy is preferred.

Related links

Management of partners

There is no evidence that treatment of male partners is necessary, unless they have symptoms. This condition is common in lesbian women and there is some evidence that treatment of female partners of an index case may be beneficial.


Review the patient if symptoms persist.

Public health issues

This is not a notifiable disease.

Symptomatic partners should be investigated.