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Bacterial vaginosis

Last reviewed: September 2023

Author(s): Dr Libby Whittaker, Medical Writer, New Zealand (2023)
Previous contributors: Dr Darion Rowan and A/Prof Amanda Oakley, Dermatologists (2018)

Reviewing dermatologist: Dr Ian Coulson

Edited by the DermNet content department


What is bacterial vaginosis?

Bacterial vaginosis (BV) is a common cause of abnormal vaginal discharge resulting from an imbalance of vaginal bacteria. Some patients have findings consistent with bacterial vaginosis on bacteriological culture but are asymptomatic. It is not considered a sexually transmitted infection (STI), although sexual activity is a risk factor.

BV was formerly called non-specific vaginitis or Gardnerella vaginitis.

Who gets bacterial vaginosis?

Bacterial vaginosis affects those with a vagina of reproductive age. Similar laboratory findings are common in postmenopausal women.

A 2019 meta-analysis (Peebles et al) reported the overall prevalence of BV to be 23–29% in women of reproductive age across several regions worldwide. 

Epidemiology has been found to vary internationally, as well as by ethnic group. In the United States, for example, the prevalence of BV was highest in black patients (22–51%), followed by Hispanic patients (16–32%), while white and Asian patients had the lowest rates (9–24% and 6–11% respectively). Similarly, in the United Kingdom, antenatal BV prevalence was higher in Afro-Caribbean patients (41%) than white (12%) or Asian patients (6%). 

What causes bacterial vaginosis?

Bacterial vaginosis (BV) is due to a disturbance of normal bacterial equilibrium (or microbiome) in the vagina. It is associated with elevated vaginal pH (>4.5). 

Lactobacilli are usually the most common type of bacteria in the vagina. In BV, there is an overgrowth of other (often anaerobic) types of bacteria, especially Gardnerella vaginalis, Mycoplasma hominis, Ureaplasma urealyticum; and Prevotella, Bacteroides, Peptostreptococcus, Mobiluncus, and Clostridiales species. 

A study assessing vaginal biopsy specimens found that Gardnerella vaginalis predominated in epithelial biofilms in patients with BV. 

BV is not generally considered sexually transmitted or contagious. There is no singular causative organism, and there is no clear equivalent disease in male partners. However, being sexually active is a risk factor for BV, and studies in women who have sex with women suggest that transmission of vaginal bacteria between sexual partners may play a role in some cases. 

Other predisposing factors for BV include:

  • Douching
  • Unprotected sexual intercourse with a male partner (as semen has a more alkaline pH than the vagina)
  • Recent use of broad-spectrum antibiotics
  • Cigarette smoking. 

Having an intrauterine device (IUD) may increase the risk of BV, although the association is not entirely clear. Irregular and prolonged vaginal bleeding has been suggested as a potential mechanism, as the pH of blood is also more alkaline than the vaginal pH.

No genetic polymorphisms associated with BV have been identified to date.

What are the clinical features of bacterial vaginosis? 

  • At least 50% of women with findings suggestive of bacterial vaginosis on bacteriological culture are asymptomatic.
  • The most common symptom is abnormal vaginal discharge: usually white/yellow/grey, thin, watery, homogenous, and sour or fishy smelling.
  • In BV alone, the vulva and vagina are not inflamed, although abnormal discharge can sometimes cause mild irritation of the surrounding skin.

What are the complications of bacterial vaginosis?

  • Emotional effects and impact on self-esteem and sexual activity, particularly with recurrent symptomatic BV.
  • BV has been associated with a higher risk of contracting sexually transmitted infections (STI) and human immunodeficiency virus (HIV), and an increased risk of pelvic inflammatory disease (PID).
  • In pregnancy, untreated BV may increase the risk of chorioamnionitis, preterm delivery, and low birth weight. 

How is bacterial vaginosis diagnosed?

History and examination

Often bacterial vaginosis (BV) is suspected on history taking, particularly in patients with recurrent BV. 

In patients presenting with abnormal vaginal discharge, take a sexual history to identify risk factors, and ask about urinary symptoms, vaginal bleeding, chance of pregnancy, and symptoms of pelvic inflammatory disease (PID) such as:

  • Abdominal pain
  • Nausea/vomiting
  • Subjective fevers
  • Malaise/feeling unwell.


  • Vital signs (tachycardia and pyrexia may suggest PID)
  • Abdominal examination to assess for uterine/suprapubic or adnexal tenderness
  • Urine dipstick and a urinary pregnancy test if indicated
  • Pelvic examination should be offered to help identify other differential diagnoses — in BV alone there is no vaginitis evident.


Diagnosis is generally confirmed on a vaginal swab. Nugent’s criteria are laboratory-based using microscopy and Gram stain, and are considered the gold standard. Other laboratory methods such as molecular diagnostic assays or nucleic acid amplification tests (NAATs) may be available depending on location. 

  • Testing for BV is generally only recommended in patients presenting with symptoms such as abnormal or malodorous vaginal discharge.
    • Exceptions where asymptomatic patients may be tested (depending on local guidelines) include prior to IUD insertion, termination of pregnancy, or in pregnant women.
  • Swabs can be self-collected, or if done by a clinician a vaginal swab should be taken prior to speculum examination (to avoid contamination with lubricant).
  • In sexually active patients, STI testing is also recommended as STIs can present similarly to BV, or co-occur.

Point-of-care testing may be used in centres with equipment and training to perform microscopy in-clinic. Amsel’s criteria, for example, is based on saline microscopy, where 3/4 criteria should be met for diagnosis:

  • Thin white or yellow homogenous vaginal discharge
  • Elevated vaginal pH (>4.5)
  • Clue cells visible on microscopy
  • Positive ‘whiff test’ ie, a fishy odour provoked by adding 10% potassium hydroxide solution to the slide-mounted specimen.

What is the differential diagnosis for bacterial vaginosis?

What is the treatment for bacterial vaginosis?

Bacterial vaginosis naturally fluctuates and treatment is not always necessary, especially if asymptomatic.

General measures

  • Avoid douching or bathing with bubble baths or other non-pH balanced detergents.
  • Regular condom use (if applicable).

Specific measures

  • Oral metronidazole (400-500mg BD for 1 week) if symptomatic (note it is important to avoid consumption of alcohol while taking metronidazole and for 48 hours afterwards).
    • Alternative treatment option: single oral dose of 2g metronidazole (less effective than 1-week course).
    • If metronidazole is contraindicated, alternatives include oral ornidazole or tinidazole (avoid in pregnancy) or clindamycin.
    • Recently, oral secnidazole has also been approved by the United States Food and Drug Administration (FDA) for the treatment of BV.
  • Intravaginal metronidazole or clindamycin may be used instead, if available.
  • Oestrogen cream may be suitable for postmenopausal women with atrophic vulvovaginitis.

How do you prevent bacterial vaginosis?

Prevention strategies for bacterial vaginosis (BV) focus on maintaining a normal vaginal pH and balance of bacteria.

Recommendations include:

  • Avoid douching
  • Wash genital area with water only; avoid using soap, vaginal wipes, or antiseptics
  • Wear cotton underwear
  • Use condoms.

Some patients may find vaginal health probiotics containing lactobacilli or vaginal acidification (eg, using lactic or boric acid) helpful for BV treatment or prophylaxis, although further high-quality randomised trials are needed to draw clear conclusions regarding their efficacy.

What is the outcome for bacterial vaginosis?

BV is often self-limiting, and generally only requires antibiotic treatment if symptomatic. Symptomatic patients usually respond well to treatment with metronidazole. Recurrence (or treatment failure) can be an issue in up to 58% of patients. 

Usually, BV is not associated with serious complications. However, it has been associated with pelvic inflammatory disease; obstetric issues such as preterm delivery if untreated during pregnancy; and it can cause distress and frustration, particularly in those who experience multiple recurrences. 



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