Aetiology and assessment of bacterial vaginosis in adults

Bacterial vaginosis is a polymicrobial syndrome caused by a reduction of the hydrogen peroxide–producing Lactobacillus species in the vagina, and overgrowth of anaerobic (eg Mobiluncus species) and other fastidious bacteria (including Gardnerella vaginalis and Atopobium vaginae)Ong, 2023Workowski, 2021. Although it is a common cause of malodorous vaginal discharge, around 50% of adults with bacterial vaginosis are asymptomaticOng, 2023.

Microscopy of a vaginal smear is key to the diagnosis of bacterial vaginosis. Culture is not required because many organisms identified by culture are commonly present in low numbers in healthy vaginal flora. If microscopy is performed, consider the followingArya, 2001:

  • Gardnerella vaginalis has been associated with bacterial vaginosis. However, treatment is not required unless there are symptoms and microscopic evidence of bacterial vaginosis.
  • Mycoplasma hominis and Ureaplasma species are common commensal organisms in sexually active females1.
  • Streptococcus agalactiae (group B streptococcus [GBS]) is a commensal organism of the gastrointestinal and genital tracts in up to 30% of healthy females of childbearing age. Although group B streptococcus has been associated with symptomatic vulvovaginitis, other causes of vulvovaginitis are more common. Other than in pregnancy, it is generally an incidental finding. If group B streptococcus is identified in a pregnant patient, see Prevention of neonatal Streptococcus agalactiae (group B streptococcus) disease.

The Amsel criteria can be used to diagnose bacterial vaginosis; 3 of the following features must be presentOng, 2023Workowski, 2021:

  • thin, white, homogeneous discharge
  • vaginal fluid pH more than 4.5
  • clue cells (epithelial cells covered with small, curved coccobacilli and mixed flora) visualised on a wet preparation of a vaginal swab or Gram-stained smear
  • fishy odour when adding alkali (potassium hydroxide 10%) to discharge.

In a patient with suspected bacterial vaginosis, also consider other diagnoses such as:

1 In this topic, the term ‘female’ is used to include all people presumed female at birth. Return