Bacterial vaginosis (BV) is common and causes a vaginal discharge, often with a noticeable smell. BV is NOT a sexually transmitted infection. It is caused by an overgrowth of normal bacteria in the vagina. Symptoms are often mild, and BV may clear without treatment. Other cases can be treated with antibiotics.
What is bacterial vaginosis and what are the symptoms?
Bacterial vaginosis (BV) is a common condition of the vagina caused by an overgrowth of various bacteria (germs). It is not just one simple infection caused by one type of bacterium.
- The main symptom of BV is a vaginal discharge. BV is one of the most common causes of vaginal discharge in women of childbearing age. The discharge is often white-grey in colour, and often has a fishy smell. The smell may be more noticeable during sex. The discharge tends to be heaviest just after a period, or after sex.
- The discharge does not usually cause itch or soreness around the vagina and vulva.
- Many women with BV do not have any symptoms (up to half of cases). BV may be found by chance when vaginal swabs are taken for other reasons.
Note: BV is not the only cause of a vaginal discharge. Various conditions can cause discharge. For example, another common cause of vaginal discharge is thrush (an infection caused by a yeast called candida). Unlike BV, thrush typically causes a thicker white discharge which tends to cause itching and soreness around the vagina and vulva. (See separate leaflet called Vaginal thrush for more information.) Sexually transmitted infections (STIs), such as chlamydia, may also cause vaginal discharge. (See separate leaflet called Genital chlamydia for more information.)
What causes bacterial vaginosis?
BV is not caused by a single bacterium (germ). In BV, an overgrowth of various bacteria occurs in the vagina. It is not clear why this happens. Normally, there are various different types of harmless bacteria in the vagina. These bacteria help in the defence against harmful germs (such as candida which causes thrush). In BV, there is a change in the balance of the normal bacteria in the vagina. As a result, certain bacteria multiply and thrive much more than usual. Some bacteria become much more prominent than they normally are.
Doctors describe these changes as "a change in the bacterial flora of the vagina from mainly Lactobacillus species to high concentrations of anaerobic bacteria".
BV is not caused by poor hygiene. In fact, excessive washing of the vagina may alter the normal balance of bacteria in the vagina, which may make BV more likely to develop.
Who gets bacterial vaginosis and how common is it?
About 1 in 3 women have BV at some time in their life. It may even be more common than this, as many cases are mild and cause no symptoms. Any woman can be affected by BV. BV is more common in women who have an intrauterine contraceptive device (IUCD). It may also be more common in women who smoke. Hormone changes during your menstrual cycle as well as genetics may also play a part.
Is bacterial vaginosis a sexually transmitted disease?
No, BV can affect any woman, including those who do not have (or who have never had) sex. However, BV is more common amongst sexually active women than amongst non-sexually active women. No bacterium is passed on between sexual partners to cause this condition. Sexual partners of women with BV do not need any treatment. However, some cases of BV seem to be sexually related. It may develop after a change in sexual partner. In these cases, the infection is not caught from anyone. But a change in sexual partner may affect the balance of normal bacteria in the vagina. BV is also more likely in women in same sex relationships who have had a change of partner.
How is bacterial vaginosis diagnosed?
The typical discharge and its characteristic fishy smell makes BV likely. In women in a regular, monogamous relationship, your doctor or nurse may be happy to diagnose BV just by your typical symptoms. However, there are some tests available that can help to confirm the diagnosis. Also, if you are pregnant, it is important to make an accurate diagnosis if you have vaginal discharge so that any infection can be treated effectively. This will mean having one or more of the tests below.
Testing the acid level of your vagina
The discharge of BV has a typical pH level (acid/alkaline balance) compared to other causes of discharge. (The overgrowth of the bacteria of BV causes the pH to change in the vagina so that it becomes more alkaline, ie the pH rises.) If available, your doctor or nurse may suggest that they take a sample of your discharge and test it with some pH paper. In addition, if an alkali is added to a sample of the discharge, it often causes a characteristic fishy smell.
Taking a sample (a swab)
To confirm the diagnosis, your doctor or nurse may also suggest that a sample (a swab) of your discharge be taken from your vagina and sent to the laboratory for testing. Large numbers of various bacteria that occur with BV are seen under the microscope. Your doctor or nurse may suggest that they take more than one swab from your vagina to rule out other causes of vaginal discharge.
What are the possible complications with bacterial vaginosis?
BV and pregnancy
If you have untreated BV during pregnancy, you have an increased risk of developing some complications of pregnancy. Early labour, miscarriage, having a low birth-weight baby or developing an infection of the uterus (womb) after childbirth can be associated with BV infection.
BV and surgery
If you have untreated BV, the chance of developing an infection of the uterus is higher following certain operations (such as termination of pregnancy or a vaginal hysterectomy). However, antibiotics are usually given before these types of surgery, and certainly if you are known to have BV infection.
BV and other infections
If you have untreated BV, you may have an increased risk of developing HIV infection if you have sex with someone who is infected with HIV. There is also some evidence that women with untreated BV may be at an increased risk of developing pelvic inflammatory disease (PID). (See leaflets called HIV and AIDS and Pelvic inflammatory disease.)
What is the treatment for bacterial vaginosis?
Not treating is an option for some women
BV is often asymptomatic (it causes no symptoms), or the symptoms are mild. Also, there is a good chance that BV will gradually clear without treatment. Any disruption in the balance of vaginal bacteria may be corrected naturally, with time. So, if you have no symptoms or only mild symptoms, you may not need any treatment.
However, if you are pregnant and you are found to have BV but have no symptoms, you may still be advised to take antibiotic treatment. The benefits of treating pregnant women with BV and no symptoms is a little uncertain. Your doctor may seek advice from a gynaecologist about whether or not you need treatment.
Note: all pregnant women who have symptoms due to BV should be offered treatment. If you are found to have BV and are undergoing a termination of pregnancy, treatment with antibiotics may also be advised even if you are asymptomatic. This is because there is a risk of BV causing a more serious infection of the uterus (womb) or pelvis after the procedure if it is not treated. Some doctors also suggest antibiotics for women with BV (and no symptoms) who are about to undergo other gynaecological procedures such as an endometrial biopsy - a biopsy of the lining of the womb.
A course of metronidazole tablets is the common treatment. Metronidazole is an antibiotic. It clears BV in most cases. Read the leaflet that comes with the tablets for a full list of possible side-effects and cautions. However, main points to note about metronidazole include:
- The usual dose is 400-500 mg twice a day for 5-7 days. A single dose of 2 grams is an alternative, although this may be less effective and may cause more side-effects. (Note: this single dose is not recommended if you are pregnant.) If you are taking the 7-day course, it is important to finish the course and not to miss any tablets.
- Some people feel sick or may vomit when they take metronidazole. This is less likely to occur if you take the tablets straight after food. A metallic taste is also a common side-effect.
- Do not drink any alcohol while taking metronidazole, and for at least 48 hours after stopping treatment. The interaction with alcohol can cause vomiting and other problems such as flushing and an increased pulse rate.
- Breast-feeding: metronidazole can get into breast milk but will not harm your baby. However, oral metronidazole is not recommended and instead you should use vaginal metronidazole or clindamycin.
Alternative antibiotic treatments
Metronidazole vaginal gel or clindamycin vaginal cream placed inside the vagina can be used if you prefer this type of treatment, or have unpleasant side-effects with metronidazole tablets. The ability of these treatments to clear BV is about the same as metronidazole taken by mouth.
Note: as with metronidazole tablets, you should avoid alcohol while using metronidazole gel and for at least 48 hours after stopping treatment. Also, clindamycin vaginal cream can cause weakening of latex condoms and diaphragms. Therefore, during treatment and for five days after treatment with clindamycin vaginal cream, do not rely on condoms or diaphragms to protect against pregnancy and sexually transmitted diseases.
Overall, there is no strong evidence at the moment that live yoghurt or Lactobacillus acidophilus (found in certain commercial probiotic products) is helpful in treating or preventing BV.
Do I need a test of cure?
Women who are not pregnant
After treatment, you do not need any further tests (such as swab tests) to ensure that BV has cleared (a test of cure) provided that your symptoms have gone.
Women who are pregnant
If you are pregnant, it is suggested that you do have a swab test taken one month after treatment, to ensure that BV is no longer present.
If you have a recurrence of symptoms and did not have any swab tests taken initially, your doctor or nurse may suggest that they take swab tests now. This is to confirm that it is BV causing your symptoms.
BV may recur if you did not complete your course of antibiotics. However, even if you have completed a full course of antibiotics, BV recurs within three months in around 1 in 3 women. If it does recur, a repeat course of antibiotics will usually be successful. A small number of women have repeated episodes of BV, and need repeated courses of antibiotics.
If you have an intrauterine contraceptive device (IUCD) and have recurrent BV, your doctor or nurse may suggest that they remove your IUCD to see if this helps to improve your symptoms. You will need to discuss alternative contraception measures with them.
How can I prevent further episodes of bacterial vaginosis?
Most episodes of BV occur for no apparent reason, and cannot be prevented. However, the following are thought to help prevent some episodes of BV. The logic behind these tips is to try not to upset the normal balance of bacteria in the vagina:
- Do not push water into your vagina to clean it (douching). The vagina needs no specific cleaning.
- Do not add bath oils, antiseptics, scented soaps, perfumed bubble bath, shampoos, etc, to bath water.
- Do not use strong detergents to wash your underwear.
- Do not wash around your vagina and vulva too often. Once a day is usually enough.
Further reading & references
- Management of bacterial vaginosis, British Association for Sexual Health and HIV (May 2012)
- Bacterial vaginosis; NICE CKS, March 2009
- Curran D, Bacterial Vaginosis, Medscape, Apr 2012
- Brotman RM, Ghanem KG, Klebanoff MA, et al; The effect of vaginal douching cessation on bacterial vaginosis: a pilot study. Am J Obstet Gynecol. 2008 Jun;198(6):628.e1-7. Epub 2008 Mar 4.
- McDonald HM, Brocklehurst P, Gordon A; Antibiotics for treating bacterial vaginosis in pregnancy. Cochrane Database Syst Rev. 2007 Jan 24;(1):CD000262.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Tim Kenny
Dr Katrina Ford
Prof Cathy Jackson