Bacterial Vaginosis - an update
Bacterial Vaginosis - an update |
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Key Words: discharge, odour, vaginal pH, lactobacilli, clue cells, preterm delivery.
Aetiology
Bacterial vaginosis (BV) is due to an overgrowth of anaerobic bacteria, genital mycoplasms and Gardnerella vaginalis (all of which can be present in small numbers in the vagina). This overgrowth is accompanied by reduction in the protective lactobacilli. Although it does appear to be more frequent in women with greater numbers of sexual partners it is not considered a sexually transmitted infection1. Risk factors for BV are smoking1, vaginal douching and using an IUCD as contraception. Black race has also been described as a risk factor, but in studies that have been able to adjust for vaginal douching (which is more commonly practised in black women), black race is not significantly associated with BV2.
Prevalence rates
It is the most frequently seen vaginal infection worldwide. Although the percentage of women with it may vary from one country to another, it is always the most common infection. Prevalence rates vary depending on the population being studied. The rates in the United Kingdom are about 15% in pregnant women3, 20-25% in women undergoing termination of pregnancy and 30% in women attending Genitourinary Medicine clinics. In studies from African countries, rates of over 50% have been reported.
Presentation and clinical features
Many women with BV have no symptoms. It is thought that about 50% will be asymptomatic. If present, the main symptoms are increased vaginal discharge and malodour (the unpleasant smell is caused by the production of volatile amines by anaerobic bacteria). The odour is often worse after sexual intercourse and during menstruation. On examination the discharge may be visible on the labia and fourchette. In the vagina the discharge (which may be frothy) is milky and adherent to the vaginal walls. There is no inflammation of the vulva or vagina4. There is increasing evidence that the bacteria can ascend the genital tract into the uterus causing endometritis (see below) and, intermenstrual bleeding has been reported with BV.
There are a number of serious complications associated with BV. It increased vaginal cuff cellulitis following hysterectomy and post-partum endometritis following caesarean section. It causes post-abortal pelvic inflammatory disease (PID) after surgical termination of pregnancy. It is an independent risk factor for preterm birth, increasing the risk of premature delivery between 1.4 - 7 times normal3. It also increases the risk of mid-trimester miscarriage 3 to 4 fold3 and doubles the risk of first trimester miscarriage5. Women with BV but without any symptoms or signs of upper genital tract inflammation have been found to have plasma cell endometritis on endometrial biopsy6. Clinical signs of pelvic inflammatory disease have been found significantly more frequently in women with BV that those with normal vaginal flora. It also increases a woman`s risk of acquiring HIV infection7.
Diagnosis
In 1983, an International Working Group formulated clinical criteria for the diagnosis of BV - known as the composite or Amsel criteria. These are now considered the "Gold standard" method of diagnosis. Three of the following should be present: thin homogenous discharge on examination, clue cells on microscopy ( at least 20% of all epithelial cells), vaginal pH greater than 4.5, amine odour after adding 10% potassium hydroxide to the vaginal fluid4. The pH should be determined using narrow-range pH paper. The vaginal swab can be touched onto the paper or the paper can be pressed against the lateral vaginal walls with sponge holders. A wet mount of vaginal secretions should be taken to look for clue cells. These are epithelial cells covered with bacteria that are "clues" to the diagnosis. To perform the amine test, a loop of vaginal secretions should be mixed with 10% potassium hydroxide on a glass slide. The mixture should be smelt immediately for the transient "dead fish" odour. Menses, within 24 hours of sexual intercourse and trichomonas vaginalis can all give a raised pH and positive amine test.
These composite criteria can be difficult to perform outside the GU Clinic setting. Recent studies have shown that a Gram-stained vaginal smear is easier to use than the composite criteria and has good sensitivity and specificity for the diagnosis of BV3. To take a vaginal smear for Gram stain, a swab should be rubbed against the lateral vaginal walls and rolled across a glass slide and allowed to air dry. The slide can then either be Gram stained and interpreted microscopically on-site, or transported to a laboratory for interpretation. This is probably the easiest and most accurate way of diagnosing BV in clinics such as obstetrics and gynaecology, general practice and family planning. Culture of vaginal secretions is not a diagnostic test for BV; 30-50% of women are colonised with G. Vaginalis as part of their normal vaginal flora.
Management
The most effective treatments are oral metronidazole, metronidazole vaginal gel and clindamycin vaginal cream8. Recommended regimens are:
All of these treatments have 70-80% cure rate at 4 weeks. Clindamycin cream may weaken condoms. As BV is an imbalance of the vaginal bacteria with lack of lactobacilli and a raised vaginal pH, yoghurt, acetic acid gel, lactic acid gel and oestrogen creams have all been suggested as treatments but none are more effective than placebo. There have been several randomised placebo-controlled trials looking at the effect of treatment of the male partner. None of them have shown any reduction in recurrent rate of BV with active treatment. Sexual partners therefore do not need to be treated. Recurrent BV may be due to persistence of BV-associated bacteria following treatment or failure to re-establish normal lactobacilli following therapy. With a rise in pH, proliferation of the colonising anaerobes and Gardnerella occurs. This explains why BV can recur after menstruation, douching and sex.
Pregnancy and breast-feeding
Women with a previous pre-term birth have been shown to have a beneficial effect from treatment of BV in subsequent pregnancies. These women may benefit from screening during further pregnancies and treatment if found to have BV. However the published randomised placebo-controlled trials in all pregnant women have not shown any treatment benefit, so there is as yet no evidence to support screening all pregnant women for BV.
References
Larsson P-G, Platz-Christensen J-J, Sundstrom E. Is bacterial vaginosis a sexually transmitted disease? Int J STD & AIDS 1991;2:362-4.
Rajamanoharan S, Low N, Jones SB , Pozniak A. Bacterial vaginosis, ethnicity and the use of genital cleaning agents: a case control study. Sex Transm Dis 1999;26:404-9.
Hay PE, Lamont RF, Taylor-Robinson D, Morgan DJ, Ison C, Pearson J. Abnormal bacterial colonisation of the genital tract and subsequent preterm delivery and late miscarriage. BMJ 1994; 308:295-8.
Hillier S, Holmes KK. Bacterial vaginosis. In: Holmes KK et al eds Sexually Transmitted Diseases. McGraw-Hill, 1999:563-586.
Ralph SG, Rutherford AJ, Wilson JD. Influence of bacterial vaginosis on conception and miscarriage in the first trimester: cohort study BMJ 1999;319:220-3.
Korn AP, Bolan G, Padian N, Ohm-Smith M, Schachter J, Landers DV. Plasma cell endometritis in women with symptomatic bacterial vaginosis. Obstet Gynaecol 1995;85:387-90.
Taha TE, Hooever DR Dallabetta GA, Kumwenda NI, Mtimavalye LAR, Yang L-P et al. Bacterial vaginosis and disturbances of vaginal flora: association with increased acquisition of HIV. AIDS 1998;12:1699-1706.
Management of bacterial vaginosis. Drugs and Therapeutics Bulletin 1998 Vol 36 No 5 33-35.
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