Levels of evidence (I-IV) and grades of recommendation (A-C) are defined at the end of the "Major Recommendations" field.
Two approaches are available:
- Amsel criteria. At least three of the four criteria are present for the diagnosis to be confirmed.
- Thin, white, homogeneous discharge
- Clue cells on microscopy of wet mount
- pH of vaginal fluid >4.5
- Release of a fishy odour on adding alkali (10% potassium hydroxide [KOH])
- A Gram stained vaginal smear, evaluated with the Hay/Ison criteria or the Nugent criteria.
The Hay/Ison criteria are defined as follows:
- Grade 1 (Normal): Lactobacillus morphotypes predominate
- Grade 2 (Intermediate): Mixed flora with some Lactobacilli present, but Gardnerella or Mobiluncus morphotypes also present
- Grade 3 (Bacterial vaginosis [BV]): Predominantly Gardnerella and/or Mobiluncus morphotypes. Few or absent Lactobacilli
There are additional grades which have not been correlated with clinical features: grade 0 No bacteria present; grade 4 Gram-positive cocci predominate.
The Nugent score is derived from estimating the relative proportions of bacterial morphotypes to give a score between 0 and 10. A score of <4 is normal, 4 to 6 is intermediate, and >6 is BV.
The Bacterial Special Interest group of British Association for Sexual Health and HIV (BASHH) recommend using the Hay/Ison criteria in Genitourinary medicine clinics (C).
- Isolation of Gardnerella vaginalis cannot be used to diagnose BV because it can be cultured from the vagina of more than 50% normal women (IIa).
BV may co-exist with other causes of abnormal discharge such as candidiasis, trichomoniasis, and cervicitis.
Patients should be advised to avoid vaginal douching, use of shower gel, and use of antiseptic agents or shampoo in the bath (C).
Treatment is indicated for:
- Symptomatic women (A)
- Women undergoing some surgical procedures (A)
- Women who do not volunteer symptoms may elect to take treatment if offered. They may report a beneficial change in their discharge following treatment. (C)
- Metronidazole 400 mg twice daily for 5-7 days (A)
- Metronidazole 2 g single dose (A)
- Intravaginal metronidazole gel (0.75%) once daily for 5 days (A
- Intravaginal clindamycin cream (2%) once daily for 7 days (A)
- Tinidazole 2 g single dose (A)
- Clindamycin 300 mg twice daily for 7 days (A)
- With metronidazole treatment alcohol should be avoided because of the possibility of a disulfiram-like action. There are no data on the risks from consuming alcohol with intravaginal metronidazole gel, but it is not recommended at present.
- Clindamycin cream can weaken condoms, which should not be used during such treatment. Pseudomembranous colitis has been reported with both oral clindamycin and clindamycin cream.
Allergy to metronidazole is uncommon. Use 2% clindamycin cream for metronidazole allergic women.
Pregnancy and Breast Feeding
Meta-analyses have concluded that there is no evidence of teratogenicity from the use of metronidazole in women during the first trimester of pregnancy (Ia).
The results of clinical trials investigating the value of screening for and treating BV in pregnancy have been conflicting. It is therefore difficult to make firm recommendations. A detailed discussion of trials in pregnancy is outside the scope of this guideline. The most recent Cochrane review concluded that there is little evidence that screening and treating all pregnant women with asymptomatic BV will prevent preterm birth and its consequences. However there is some suggestion that treatment before 20 weeks gestation may reduce the risk. In conclusion:
- Symptomatic pregnant women should be treated in the usual way (B).
- There is insufficient evidence to recommend routine treatment of asymptomatic pregnant women who attend a genitourinary clinic and are found to have BV.
- Women with additional risk factors for preterm birth may benefit from treatment before 20 week gestation.
Metronidazole enters breast milk and may affect its taste. The manufacturers recommend avoiding high doses if breast feeding. Small amounts of clindamycin enter breast milk. It is prudent therefore to use an intravaginal treatment for lactating women (C).
Termination of Pregnancy (TOP)
Three studies have investigated whether antibiotics can reduce the rate of infectious morbidity in women with BV, following termination of pregnancy. A Scandinavian study of 231 women demonstrated a reduction in post-TOP infection by treating BV with oral metronidazole before termination (Ib). Another demonstrated a reduction in infective complications following the use of clindamycin cream (Ib). A United Kingdom study of 273 women again found a reduction in post-operative upper genital tract infection from 16% to 8.5%, but did not quite reach statistical significance. There are no data on the effectiveness of treatment administered at the time of TOP.
- These studies support screening for and treating BV with either metronidazole or clindamycin cream, to reduce the incidence of subsequent endometritis and pelvic inflammatory disease (PID) (Ia).
Human Immunodeficiency Virus (HIV) Infection
Women with HIV have not been shown to respond differently to treatment for BV than those without. In an as yet unpublished study BV was a risk factor for female to male HIV transmission so there may be rationale for attempting to suppress BV or treat recurrence rapidly in discordant couples.
- No reduction in relapse rate was reported from two studies in which male partners of women with bacterial vaginosis were treated with metronidazole, one study of tinidazole, and one of clindamycin (Ib). Routine screening and treatment of male partners are therefore not indicated.
- Two studies reported a high incidence of bacterial vaginosis in female partners of lesbians with BV (II). No study has investigated the value of treating partners of lesbians simultaneously.
A test of cure is not required if symptoms resolve.
Several published studies have evaluated treatments for women with frequent recurrences of BV.
- Suppressive 0.75% metronidazole vaginal gel. In one placebo controlled randomised trial 0.75% metronidazole vaginal gel twice a week for 16 weeks was superior to placebo with 70% of women being relapse-free compared to 39% in the placebo group. However, only 34% of patients remained cumulatively free of recurrence 12 weeks after stopping treatment, compared to 22% of controls. There was an excess of vulvovaginal candidosis in those receiving metronidazole: 43% compared to 21%.
- Probiotic therapy. A double blind randomised controlled trial of probiotic lactobacilli applied daily on days 1-7 and 15-21, in 117 women showed significantly lower recurrence rates over the ensuing two months in women with at least two episodes of BV in the preceding year: BV (15.8% [9/57 women] versus 45.0% [27/60 women]).
- Antibiotics and probiotic therapy. A Swedish study of 76 women whose BV resolved following a course of clindamycin cream were randomised to receive human lactobacilli or placebo. At the end of the study, 65% (24/37) of the lactobacilli treated women remained BV-free compared to 46% (18/39) of the placebo treated women.
- Lactic acid gel and acetic acid gel (the latter is no longer available in the UK) have not been evaluated adequately in well-designed RCTs.
- A detailed explanation of BV should be provided, reinforced with clear and accurate written information (C [IV]).
When giving information to patients, the clinician should consider the following:
- An explanation of what treatment is being given, how to take it, and its possible adverse effects
- That following treatment BV can recur, but will respond to standard treatments
- Partners do not need to be screened routinely. Some clinicians recommend screening male partners of women with recurrent BV for urethritis, as it was associated with BV in one study.
Routine sexually-transmitted infection (STI) screening should be offered in accordance with current testing guidelines.
Levels of Evidence
Ia: Evidence obtained from meta-analysis of randomised controlled trials
Ib: Evidence obtained from at least one randomised controlled trial
IIa: Evidence obtained from at least one well-designed controlled study without randomisation
IIb: Evidence obtained from at least one other type of well-designed quasi-experimental study
III: Evidence obtained from well-designed non-experimental descriptive studies such as comparative studies, correlation studies, and case control studies
IV: Evidence obtained from expert committee reports or opinions and/or clinical experience of respected authorities
Grades of Recommendation
A (Evidence Levels Ia, Ib)
- Requires at least one randomised controlled trial as part of the body of literature of overall good quality and consistency addressing the specific recommendation.
B (Evidence Levels IIa, IIb, III)
- Requires availability of well conducted clinical studies but no randomised clinical trials on the topic of recommendation.
C (Evidence Level IV)
- Requires evidence from expert committee reports or opinions and/or clinical experience of respected authorities.
- Indicates absence of directly applicable studies of good quality.