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Bacterial vaginosis (BV) is the most common cause of abnormal discharge in women of reproductive age.1
Though the exact aetiology is unknown, the broad pathophysiology is that BV is caused by a loss of the normal flora which inhabits the vaginal canal with a simultaneous increase in anaerobic bacteria. This leads to a rise in pH and alterations in the consistency, composition and odour of vaginal discharge.2
Up to 84% of patients are asymptomatic and many individuals are unwilling to seek medical advice due to perceived stigma and embarrassment surrounding vaginal health.
One study in the United States demonstrated that around 29.2% of the general female population of reproductive age had BV at any one time, with only 15.7% being symptomatic.3,4
Typically, the vagina has an acidic pH of less than 4.5. This is an ideal environment for lactobacilli to thrive (Figure 1).
Occasionally, environmental factors can trigger a pH rise in the vaginal canal. When the pH is elevated above 4.5, the environment becomes too hostile for lactobacilli to survive.
Once the normal flora of the vagina has decreased, irregular bacteria such as Gardnerella vaginalis, Prevotella spp., Mycoplasma hominis and Mobinculus spp. (amongst others) can begin to proliferate (Figure 2). This leads to an altered composition of vaginal discharge, leading to changes in consistency and smell.
Risk factors for BV include:1,3
Sexual activity: especially unprotected cunnilingus. It is important to note that whilst BV is sexually associated, it is not a sexually transmitted infection
Grade 2 (intermediate): mixed flora with some Lactobacilli present, but Gardnerella or Mobiluncus morphotypes also present
Grade 3 (BV): predominantly Gardnerella and/or Mobiluncus morphotypes. Few or absent lactobacilli
Grade 4: gram-positive bacteria predominate
Asymptomatic individuals who are not pregnant, do not routinely require treatment as BV is usually self-limiting and resolves after 3-7 days.
General advice for patients should include:
Avoid vaginal douching
Avoid bubble baths, shower gel and antiseptic products near the genitals
Some patients find probiotics useful. This can be in the form of dietary intake (kimchi, kefir, kombucha etc), tablet or vaginal pessary. Research suggests this can be useful, though there is no conclusive evidence yet.7
Medical treatment is recommended for certain groups of individuals with BV. This includes anyone with symptoms and any pregnant individuals, regardless of choice in continuation of pregnancy.
All the following treatments are believed to be similarly efficacious with oral metronidazole being 87-92% successful at four weeks and vaginal metronidazole at 61-94%.8
Options for treating BV include:
Oral metronidazole 400-500 mg BD for 5-7 days
Oral metronidazole 2 g stat
Oral tinidazole 2 g stat
Oral clindamycin 300 mg BD for seven days
Metronidazole vaginal gel 0.75% OD for five days
Clindamycin vaginal gel 2% OD for seven days
The treatment of choice for BV is usually oral metronidazole BD. Low-dose metronidazole is safe for use in pregnancy. However, high dose metronidazole (2g stat) should be avoided in pregnancy.
Individuals who are breastfeeding should be offered vaginal preparations. When prescribing vaginal preparations, it is important to warn patients that the ingredients may degrade condoms, therefore extra precautions should be taken to avoid unwanted pregnancy or STIs.
BV places patients at higher risk of acquiring and transmitting STIs, including chlamydia, gonorrhoea and HIV.2
Although there is a high prevalence of BV infection in women with pelvic inflammatory disease (PID), data does not suggest that BV is causative of PID.9
In pregnancy, BV is associated with first-trimester miscarriage (77%), late miscarriage (after 12 weeks – 23%), preterm labour (12.5%), low birth weight and postpartum endometritis.12,13
BV is the most common cause of abnormal vaginal discharge in women of reproductive age.
BV is caused by an overgrowth of anaerobic vaginal bacteria, which results in loss of the normal lactobacilli population and an increase in vaginal pH (>4.5).
Women are often asymptomatic (up to 84%). However, when symptomatic, patients present with a change in discharge (thin, white and offensive smelling).
Asymptomatic non-pregnant women do not require treatment.
For symptomatic or pregnant patients, the treatment of choice is 400-500mg metronidazole PO BD for 5-7 days.
It is important to treat all pregnant women, regardless of whether they are continuing with their pregnancy or having a termination due to the risk of future pregnancy complications.
BV places patients at higher risk of acquiring and transmitting STIs, including chlamydia, gonorrhoea and HIV.
Dr Frances Lander
Genitourinary Medicine Registrar
Dr Chris Jefferies
Lazaro, Dr Neil. Sexually Transmitted Infections in Primary Care (2e). s.l. : Royal College of General Practitioners, 2013.
Bertini, Marco. Bacterial Vaginosis and Sexually Transmitted Diseases: Relationship and Management. 2017.
The Prevalence of Bacterial Vaginosis in the United States, 2001–2004; Associations With Symptoms, Sexual Behaviors, and Reproductive Health. Koumans, Emilia et al. 11, s.l. : Sexually Transmitted Diseases, 2007, Vol. 34.
Attitudes and experience of women to common vaginal infections. Johnson, Sarah. et al. 4, s.l. : Journal of lower genital tract infections, 2010, Vol. 14.
Willacy, Hayley. Bacterial Vaginosis. 2020. Available from: [LINK].
Diagnostic Value of Amsel’s Clinical Criteria for Diagnosis of Bacterial Vaginosis. Mohammadzadeh, Farnaz,. et al. 3, s.l. : Global Journal of Health Science, 2015, Vol. 7.
Probiotics for the treatment of women with bacterial vaginosis. Falagas, M.E. et al. 7, s.l. : Clinical Microbiology and Infection , 2007, Clinical Microbiology and Infection, Vol. 13, pp. 657-664.
Comparison of oral and vaginal metronidazole for treatment of bacterial vaginosis in pregnancy: impact on fastidious bacteria. Mitchel, Caroline et al. 89, s.l. : BMC Infectious Diseases , 2009, Vol. 9.
Does Bacterial Vaginosis Cause Pelvic Inflammatory Disease? Taylor, Brandie,. et al. 2, s.l. : Sexually Transmitted Diseases, 2013, Vol. 40.
Randomised treatment trial of bacterial vaginosis to prevent post-abortion complication. Miller, Leslie. et al. 9, s.l. : British Journal of Obstetrics and Gynaecology, 2004, Vol. 111.
Prevention of infection after induced abortion. Achilles, Sharon. et al. 4, s.l. : Contraception, 2011, Vol. 83.
Bacterial vaginosis in association with spontaneous abortion and recurrent pregnancy losses. Gözde, Izik. et al. 3, s.l. : Journal of Cytology, 2016, Vol. 33.
The Role of Bacterial Vaginosis in Preterm Labor. Kirchner, Jeffrey T. 62, s.l. : American Family Physician, 2000, Vol. 1.
Figure 1 and 2. Dr Graham Beards. Normal and BV flora. License: [CC BY-SA]