Bacterial Vaginosis

Definition/diagnostic criteria Bacterial vaginosis (BV) is a syndrome resulting from the replacement of the normal lactobacillus-dominant vaginal flora with a high concentration of anaerobic bacteria. Technically, diagnosis may be based on Amsel’s criteria: homogenous, thin, white discharge that smoothly coats the vaginal walls; a vaginal pH >4.5; a positive whiff test with the addition of 10% KOH; and the presence of clue cells on microscopy. In practice, a more pragmatic approach may be adopted.

Epidemiology BV is the most common cause of vaginal discharge in women of childbearing age. While its exact prevalence in the UK is unknown, studies suggest a prevalence rate of 12-30% in this population. It is more common in sexually active women, though it is not strictly classified as a sexually transmitted infection.

Diagnosis
Clinical features: BV is often asymptomatic, but when symptoms occur, they typically include a thin, off-white vaginal discharge with a characteristic ‘fishy’ odour, especially after sexual intercourse or during menstruation. Itching and irritation are less common.

Investigations: Diagnosis is primarily clinical. A pH test of vaginal secretions can be useful. Cultures are generally not required as they are not specific for BV but a swab may be taken if the diagnosis is in doubt. Consider the risk of STI and refer to a sexual health clinic if necessary.

Treatment Treatment is recommended for symptomatic women or those undergoing certain gynaecological procedures. The first-line treatment for BV in non-pregnant women includes a 5- to 7-day course of oral metronidazole or a 7-day course of intravaginal clindamycin cream. Alternatively, a 2g single dose of metronidazole is also effective.

For pregnant women, oral metronidazole or clindamycin (in the second or third trimester only) is recommended. In an asymptomatic pregnant woman, discuss the issue with the patient’s obstetrician.

If the problems recurs, try an alternative treatment. If there are further recurrences, or persistence, consider advice from a department of sexual health – metronidazole vaginal gel has been used as suppressive treatment.

Prognosis BV is generally a benign condition, but it can be associated with an increased risk of developing other infections such as pelvic inflammatory disease, especially after gynaecological surgery or in the context of an IUD insertion. Recurrence is common, with up to 30% of women experiencing a recurrence within three months after treatment. Long-term complications are rare, but BV has been associated with adverse pregnancy outcomes, including preterm delivery and low birth weight.