Bacterial vaginosis is the commonest cause of abnormal discharge in women of childbearing age. It is characterized by an overgrowth of predominantly anaerobic organisms. It can arise and remit spontaneously. It is not regarded as a sexually transmitted infection.

Presentation of Bacterial Vaginosis

Bacterial vaginosis is commonly diagnosed clinically by the presence of an offensive, non-irritant vaginal discharge. This is classically described as being thin, white or grey and homogenous and may coat the walls of the vagina and vestibule. The pH of the vaginal discharge is normally in the relatively alkaline range (>4.5)

It is important to remember that approximately 50% of women are asymptomatic.

Complications of Bacterial Vaginosis

• bacterial vaginosis at the time of a termination of pregnancy has been associated with the development of post-termination of pregnancy (TOP) endometritis and upper genital tract infection.

• bacterial vaginosis at the time of vaginal hysterectomy has been associated with an increased incidence of cuff cellulitis following hysterectomy.

• bacterial vaginosis is associated with late miscarriage, pre-term birth, pre-term premature rupture of membranes and post-partum endometritis in pregnancy.

Diagnosis of Bacterial Vaginosis

Historically, bacterial vaginosis was diagnosed by using Amsel’s clinical criteria.

Amsel’s criteria — at least three of the four criteria listed below needed to be present for the diagnosis to be confirmed:

• thin, white, homogenous, vaginal discharge

• clue cells on microscopy (these are epithelial cells covered with mixed organisms)

• pH of vaginal fluid >4.5

• release of a fishy odour on adding alkali (10% KOH) to a specimen of the vaginal discharge.

Diagnosis by microscopy

In more recent years, microscopy of a Gram-stained vaginal smear has become a popular method of diagnosis. The techniques vary from detailed counting of different morphological bacterial types (Nugent criteria) to categorizing the flora into grades (Hay-Ison criteria).

In clinical situations, the grading system described by Hay et al is commonly used to make the diagnosis. The grading system is shown below:

• Grade 0 — epithelial cells only with no bacteria.

• Grade 1 — normal vaginal flora (lactobacillus morphotypes only — this is a normal smear).

• Grade 2 — intermediate vaginal flora, i.e. reduced number of lactobacillus morphotypes with a mixed bacterial flora. This grade is believed to be a transitional phase between the normal and bacterial vaginosis state.

• Grade 3 — few or no lactobacilli (indicative of bacterial vaginosis). Many different bacteria, both Gram-positive and Gram-negative are seen, which give a ‘salt and pepper’ appearance. ‘Clue cells’ are present in the majority of these smears but it is the appearance of the mixed flora that is indicative of bacterial vaginosis.

• Grade 4 — other pattern, e.g. just streptococci with no lactobacilli or organisms associated with bacterial vaginosis. Sometimes seen in smears from post-menopausal women.

Isolation of Gardnerella vaginalis cannot be used to diagnose bacterial vaginosis.

Treatment of Bacterial Vaginosis

Treatment is only indicated for symptomatic women, some pregnant women (see below) or those undergoing gynaecological surgery.

First-line treatment for bacterial vaginosis involves the use of metronidazole in a dose of 400 mg twice daily for 5 days. Alternatively, 2 g of metronidazole may be used as a single oral dose. Metronidazole needs to be taken on a full stomach. Alcohol should be avoided because of an Antabuse-like reaction that may develop.

Alternative regimens include intravaginal metronidazole gel (0.75%) used once daily for 5 days, or intravaginal clindamycin cream (2%) used once daily for 7 days or clindamycin (300 mg) taken orally twice daily for 7 days.

Oral clindamycin can cause pseudo-membranous colitis and clindamycin cream can weaken condoms.

Metronidazole allergy is uncommon. Clindamycin cream 2% is recommended for women who are allergic to metronidazole.

Recurrent bacterial vaginosis

There are few published studies evaluating the optimal approach to treating this group of women. Small studies using Aci-jel, live yoghurt or Lactobacillus acidophilus have not demonstrated a benefit. One anecdotal suggestion is to try a standard 5-day course of metronidazole 400 mg b.d. followed by suppression with weekly vaginal metronidazole gel or clindamycin cream for a few months.

Women with recurrent bacterial vaginosis are advised to avoid vaginal douching and the use of shower gel, antiseptic agents or shampoo in the bath.

Pregnancy and breast feeding

A number of randomized controlled trials have shown that women with a history of prior idiopathic pre-term birth or second trimester loss should be screened for bacterial vaginosis and receive treatment with a course of oral metronidazole, preferably early in the second trimester of pregnancy.

The results of further randomized controlled trials of screening and treating all pregnant women are awaited. One recently published study highlighted that treatment of pregnant women with asymptomatic abnormal vaginal flora and bacterial vaginosis with oral clindamycin early in the second trimester significantly reduced the rate of late miscarriage and spontaneous pre-term birth in a general obstetric population.

Although, meta-analyses have concluded that there is no evidence of teratogenicity from the use of metronidazole in women during the first trimester of pregnancy, it is best to avoid use of metronidazole in the first trimester. Clindamycin 300 mg twice daily for 7 days can be used if metronidazole is contraindicated.

It is prudent to use an intravaginal treatment for lactating women because oral metronidazole can make breast milk unpalatable.

Following treatment for bacterial vaginosis, a test of cure is not necessary. If, however, treatment is prescribed in pregnancy to reduce the risks of pre-term birth, a repeat test should be performed after 1 month and further treatment offered if the bacterial vaginosis has recurred.

Management of sexual partners

Screening and treatment of sexual partners is not indicated as the current view is that bacterial vaginosis is not transmitted sexually.

Other management

Any woman presenting with vaginal discharge should have a sexual history taken and be advised to have a screen for STIs.

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