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, and other anaerobes. 

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 to male partners
  • increased risk of other STI transmission/acquisition including gonorrhoea and herpes simplex type 2. 

STI Atlas (external link)


Bacterial vaginosis can be diagnosed if at least 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 cases, as this condition can often resolve spontaneously, but is recommended before gynaecological procedures and considered in pregnant women with a history of preterm labour. If a patient has an intrauterine device (IUD) leave IUD in place and treat as recommended. Seek specialist advice as needed.

Standard/ initial therapy

  • Metronidazole 400 mg orally, 12-hourly with food for 7 days. 


  • Metronidazole gel 0.75 per cent gel 5 g, intravaginally nocte for 5 nights (not on PBS)


  • Clindamycin 2 per cent vaginal cream 5 g, daily for 7 days (not on PBS)

Alternative therapy

  • Clindamycin 300 mg orally, 12-hourly for 7 days (not on PBS).


  • Metronidazole 2 g orally, as a single dose (less effective)

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. Vaginal douching should be avoided.

Contact tracing is not required. 

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 women who have sex with women and there is some evidence that treatment of female partners of an index case may be beneficial.

Follow up

Review the patient if symptoms persist.

Public health issues

This is not a notifiable disease.

Symptomatic partners should be investigated.