Bacterial vaginosis

Author: Dr Darion Rowan, Dermatologist, Middlemore Hospital, Auckland, New Zealand. DermNet NZ Editor-in-Chief: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Latest update, January 2018.

What is bacterial vaginosis?

Bacterial vaginosis is a common cause of abnormal vaginal discharge and malodour in women. Some women have identical findings on vaginal wet mount and culture but do not have any symptoms.

Bacterial vaginosis is not sexually transmitted or contagious. It was previously referred to as nonspecific vaginitis.

Who gets bacterial vaginosis?

Bacterial vaginosis affects women of reproductive age. Similar laboratory findings are common in postmenopausal women.

What is the cause of bacterial vaginosis?

Bacterial vaginosis is due to a disturbance of normal bacterial equilibrium (or microbiome) in the vagina. Lactobacilli are usually the most common bacteria in the vagina. In bacterial vaginosis, there is an overgrowth of other bacteria, especially Gardnerella, Bacteroides, Peptostreptococci and Mobilunculus species. These are anaerobic bacteria, that is, they grow in the absence of oxygen.

Predisposing factors for bacterial vaginosis include recent use of broad spectrum antibiotics, decreased oestrogen production (eg, post-menopause), intrauterine device (IUD) and an increased number of sexual partners. It is associated with elevated pH > 4.5 within the vagina.

What are the clinical features of bacterial vaginosis?

The odour of the creamy white foamy discharge is the most common complaint in bacterial vaginosis, with a positive "whiff" test (malodour).  The vulva and vagina are not inflamed and any vaginal burning or itching should be explained by another cause of vaginitis, especially aerobic vaginitis. The discharge can cause mild irritation of the skin around the vagina.

In most women there are no complications from bacterial vaginosis. In pregnancy, there have been reports associating bacterial vaginosis with premature labour and inflammation around the fetus (chorioamnionitis). It is possible that these complications were due to aerobic vaginitis, which is only recently being recognised as distinct from bacterial vaginosis.

How is the diagnosis of bacterial vaginosis made?

In bacterial vaginosis, a vaginal wet smear shows the normal vaginal lactobacilli are replaced by multiple small cocci. These are small round bacteria whereas lactobacilli are elongated. "Clue" cells are also seen; these are epithelial cells from the lining of the vagina with many of the cocci adherent to their cells. Vaginal pH is elevated (> 4.5) in most patients, unlike in vulvovaginal candidiasis when it is reduced below 4.5.

The flora typical for bacterial vaginosis can be a normal finding in asymptomatic postmenopausal women. 

Nugent criteria may be used to quantify Gram stain findings [1].

What is the treatment of bacterial vaginosis?

Bacterial vaginosis naturally fluctuates so treatment is not always necessary. Treatment of bacterial vaginosis is recommended during pregnancy to reduce any risk of complications related to infection.  


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