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Bacterial vaginosis

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Bacterial vaginosis article more useful, or one of our other health articles.

Bacterial vaginosis (BV) is the most common cause of abnormal vaginal discharge in women of reproductive age.

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BV is caused by an overgrowth of predominantly anaerobic organisms in the vagina. The most common organisms include Gardnerella vaginalis, Prevotella spp., Mycoplasma hominis, and Mobiluncus spp. However, many others have been identified. They replace lactobacilli, which are the dominant bacteria present in the normal vagina. The pH increases from less than 4.5 to as high as 6. BV is not thought to be sexually transmitted (it can occur in virgins); however, sexual activity has been linked to development of the infection.

Risk factors

  • Sexual activity (BV is not thought to be directly sexually transmitted; however, it is identified more frequently in those who are sexually active).

  • New sexual partner.

  • Other sexually transmitted infections (STIs).

  • Ethnicity (more common in women of Afro-Caribbean descent).

  • Presence of a copper intrauterine contraceptive device (IUCD)2 .

  • Vaginal douching.

  • Bubble baths.

  • Receptive oral sex. Women who have sex with women share similar lactobacillary types, are more likely to have concordant vaginal flora patterns, and are at increased risk for BV3 .

  • Smoking.

Protective factors

  • Combined oral contraceptive pill (oestrogen encourages lactobacilli).

  • Condom use.

  • Circumcised partner.


  • BV is the most common cause of pathological vaginal discharge in women of child-bearing age1 .

  • Reported prevalence rates vary widely. In the past, prevalence has been reported as 5% in a group of asymptomatic college students, 12% in pregnant women attending an antenatal clinic, 30% in women undergoing termination of pregnancy (TOP)3 .

  • Prevalence is higher amongst sexually active women than amongst non-sexually active women, so that sometimes the term 'sexually associated' rather than 'sexually transmitted' is used.

  • Prevalence has been reported as higher in women having sex with other women, although there may be confounding factors4 .

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  • Offensive, fishy-smelling vaginal discharge without soreness or irritation.

  • Approximately half of all women infected are asymptomatic.

  • On examination there is usually a thin layer of white discharge covering the vaginal wall.

Differential diagnosis

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Diagnosis of BV in primary care can be logistically difficult. There are two ways to diagnose BV; both rely on microscopy and may be difficult to arrange in general practice.

  • Amsel's criteria require at least three of the following for diagnosis:

    • Homogeneous discharge as above.

    • Microscopy showing vaginal epithelial cells coated with a large number of bacilli ('clue cells').

    • Vaginal pH >4.5.

    • Fishy odour on adding 10% potassium hydroxide to vaginal fluid.

  • Microscopic appearance of a Gram-stained smear of vaginal discharge analysed using the Ison/Hay criteria:

    • Grade 1: normal. Lactobacilli predominate.

    • Grade 2: intermediate. Some lactobacilli, but other organisms present.

    • Grade 3: BV. Other organisms predominate. Few or absent lactobacilli.

The isolation of G. vaginalis cannot be used as a diagnostic criterion as it is present in the normal flora of up to 40% of women. Pathology laboratories use varying methods for diagnosis of BV outside specialist clinics. Usually a swab of vaginal discharge placed on to a microscope slide is required. Sometimes the laboratory may prepare the slide from a swab.

Therefore, under certain circumstances it may be reasonable to make an empirical diagnosis. A woman can be treated empirically if1 :

  • There are typical symptoms and signs (a malodorous discharge with no soreness or irritation).

  • They are at low risk of STI (ie not aged under 25, no recent new sexual partner, not more than one sexual partner in the previous year, no past history of STI).

  • They are not postnatal or post-miscarriage.

  • They haven't recently had a TOP or gynaecological surgery.

  • They are not pregnant.

  • They have not recently had treatment for BV.

  • There are no signs of alternative causes of vaginal discharge (fever, bleeding, pain, itch).

  • There is a raised pH if pH paper is available to measure it (see below).

If empirical diagnosis/treatment is not appropriate, examine and swab as per local pathology laboratory protocol, or refer to the local genitourinary medicine (GUM) clinic for testing. If the woman is at risk of other STIs, swabs for other infections (chlamydia, gonorrhoea) should also be done.

How to measure vaginal pH

  • If pH paper is available, this can be done in primary care.

  • Take a swab from the lateral vaginal wall.

  • Take care not to swab the cervix, which has a higher pH. Blood or semen may also raise pH.

  • Roll the swab over the pH paper. Compare the colour against the standard to obtain a measurement.

  • Raised pH is suggestive of BV, but not specific. (It can be raised in other conditions such as trichomoniasis.)


  • Advise avoidance of vaginal douching5 .

  • Advise against the use of shower gel, and use of bubble bath, antiseptic agents or shampoo in the bath.

  • Asymptomatic women usually do not need treatment, unless they are pregnant. If they are having a TOP, treatment beforehand is appropriate to reduce risk of complications. If there are additional risks of preterm birth, asymptomatic pregnant women may need treatment. This should be discussed on an individual basis with their obstetrician.

  • Treatment options are1 :

    • Oral metronidazole 400-500 mg bd for 5-7 days. Treatment of choice. This may be used in pregnant women.

    • Oral metronidazole 2 g stat. Avoid in pregnant women.

    • Metronidazole vaginal gel 0.75% once daily for five days.

    • Clindamycin vaginal gel 2% once daily for seven days.

    • Oral tinidazole 2 g stat.

    • Oral clindamycin 300 mg bd for seven days.

    • Alternatives to antibiotics have been approved since the above guidelines were published - see below.

  • None of these treatment regimes is known to be superior.

  • Women who are breastfeeding should usually be prescribed intravaginal rather than oral treatment.

  • It is not necessary to have a further test to prove resolution if symptoms resolve (unless treatment is prescribed in pregnancy to reduce the risk of preterm birth, in which case a repeat test should be made after one month and further treatment offered if the BV has recurred).

  • Note that vaginal creams and gels may weaken condoms.

  • There is no need to screen partners.

  • There is no established prescribable treatment of recurrent BV but (off-licence) regular use of metronidazole gel 0.75% as a suppressive therapy may be effective.

  • Astodrimer gel (see alternatives to antibiotics below) is approved for the prevention of recurrent BV and associated symptoms. In a phase 3, randomised, double-blind, placebo-controlled study, astodrimer significantly reduced BV recurrence rates at week 16 (44.2% vs 54.3%), increased time to BV recurrence and reduced BV symptoms at 16 weeks (27.9% vs 40.6%)6 .

  • There is no evidence currently that antiseptics or disinfectants are effective in the treatment of BV7 .

  • There is mixed evidence for using probiotics against BV8 .

Alternatives to antibiotic treatment

Astodrimer is of the class of novel compounds with a surface charge. Both size and surface charge of the dendrimer contribute to the function of the compound which is to inhibit growth of bacteria by blocking their attachment to cells and inhibiting the formation of and disrupting biofilms. A double-blind, randomised, multicentre, placebo-controlled trial showed that astodrimer gel once daily for seven days was superior to placebo for treatment of BV9 .

The treatment was well tolerated and provided rapid resolution of BV symptoms. Patients found the treatment convenient and tolerable, and superior to placebo with respect to overall satisfaction and perceived efficacy. Clinical cure rates were generally favourable or comparable to those reported with conventional antibiotics.


There is, however, no evidence for screening for BV in pregnancy, as there is no evidence treating it reduces risks such as preterm birth. Similarly, there is limited evidence that treating asymptomatic women in pregnancy prevents preterm birth; hence, each woman should be assessed on an individual basis.


  • It may resolve without treatment.

  • Up to 70% of patients have a relapse within three months of successful treatment2 .

Further reading and references

  • Oduyebo OO, Anorlu RI, Ogunsola FT; The effects of antimicrobial therapy on bacterial vaginosis in non-pregnant women. Cochrane Database Syst Rev. 2009 Jul 8;(3):CD006055. doi: 10.1002/14651858.CD006055.pub2.
  • Money D; The laboratory diagnosis of bacterial vaginosis. Can J Infect Dis Med Microbiol. 2005 Mar;16(2):77-9.
  • Bautista CT, Wurapa E, Sateren WB, et al; Bacterial vaginosis: a synthesis of the literature on etiology, prevalence, risk factors, and relationship with chlamydia and gonorrhea infections. Mil Med Res. 2016 Feb 13;3:4. doi: 10.1186/s40779-016-0074-5. eCollection 2016.
  • Bradshaw CS, Sobel JD; Current Treatment of Bacterial Vaginosis-Limitations and Need for Innovation. J Infect Dis. 2016 Aug 15;214 Suppl 1:S14-20. doi: 10.1093/infdis/jiw159.
  1. Sexually Transmitted Infections in Primary Care; Royal College of General Practitioners and British Association for Sexual Health and HIV (Apr 2013)
  2. Sherrard J, Wilson J, Donders G, et al; 2018 European (IUSTI/WHO) International Union against sexually transmitted infections (IUSTI) World Health Organisation (WHO) guideline on the management of vaginal discharge. Int J STD AIDS. 2018 Nov;29(13):1258-1272. doi: 10.1177/0956462418785451. Epub 2018 Jul 27.
  3. Bacterial vaginosis; NICE CKS, July 2023 (UK access only)
  4. Forcey DS, Vodstrcil LA, Hocking JS, et al; Factors Associated with Bacterial Vaginosis among Women Who Have Sex with Women: A Systematic Review. PLoS One. 2015 Dec 16;10(12):e0141905. doi: 10.1371/journal.pone.0141905. eCollection 2015.
  5. Lewis FM, Bernstein KT, Aral SO; Vaginal Microbiome and Its Relationship to Behavior, Sexual Health, and Sexually Transmitted Diseases. Obstet Gynecol. 2017 Apr;129(4):643-654. doi: 10.1097/AOG.0000000000001932.
  6. Results of a phase 3, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of astodrimer gel for prevention of recurrent bacterial vaginosis; AJOG
  7. Verstraelen H, Verhelst R, Roelens K, et al; Antiseptics and disinfectants for the treatment of bacterial vaginosis: a systematic review. BMC Infect Dis. 2012 Jun 28;12:148.
  8. Wang Z, He Y, Zheng Y; Probiotics for the Treatment of Bacterial Vaginosis: A Meta-Analysis. Int J Environ Res Public Health. 2019 Oct 12;16(20). pii: ijerph16203859. doi: 10.3390/ijerph16203859.
  9. Waldbaum AS, Schwebke JR, Paull JRA, et al; A phase 2, double-blind, multicenter, randomized, placebo-controlled, doseranging study of the efficacy and safety of Astodrimer Gel for the treatment of bacterial vaginosis. PLoS One. 2020 May 4;15(5):e0232394. doi: 10.1371/journal.pone.0232394. eCollection 2020.
  10. Aduloju OP, Akintayo AA, Aduloju T; Prevalence of bacterial vaginosis in pregnancy in a tertiary health institution, south western Nigeria. Pan Afr Med J. 2019 May 7;33:9. doi: 10.11604/pamj.2019.33.9.17926. eCollection 2019.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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