Bacterial vaginosis

by | Women's Health

If you have a watery vaginal discharge with a strong or unpleasant odour, it’s possible you may have bacterial vaginosis (BV). Bacterial vaginosis is a common condition, thought to be caused by an imbalance in the bacteria in the vagina. BV affects about 1 in 10 women in Australia at some stage in their lives. It’s the most common type of vaginal infection in women of childbearing age – even more common than thrush.

What are the symptoms?

Up to a half of all women with BV don’t have any symptoms.

Women who do have symptoms commonly report having a thin, watery vaginal discharge that’s white or greyish in colour. There is also usually an unpleasant genital odour, often described as a strong fishy smell, that’s especially noticeable after intercourse.

Other symptoms may include mild vaginal or vulval discomfort (itching or irritation) and burning when you urinate (wee). However, these symptoms are unusual.

How do you get BV?

Bacterial vaginosis is thought to be caused by an imbalance in the types of bacteria that are normally found in the vagina. There is an overgrowth of a mix of different types of ‘bad’ bacteria (including anaerobic bacteria, or anaerobes) and not enough ‘good’ bacteria (Lactobacillus species).

While BV usually only affects women who are sexually active, including women with female sex partners, BV is currently not considered to be a sexually-transmitted infection (STI).

Male partners of women with BV are not affected. While research has shown that some of the types of bacteria involved in BV are commonly found on the skin of the penis, they don’t seem to cause any harm in men. But when these bacteria are introduced to the vagina, they can flourish and lead to BV.

Risk factors

Unprotected sexual activity with a new partner or multiple partners can increase your risk of getting bacterial vaginosis. That means sex without a condom or oral sex without a dental dam. Having a female sex partner may also increase your risk of bacterial vaginosis.

Frequent douching (using a cleanser or water to clean inside the vagina) or using medicated or perfumed soaps, shower gels or bubble baths also increase your chances of getting BV.

If you smoke you are also at increased risk of getting BV.

Tests for BV

If you think you may have a vaginal infection, you should see your doctor (GP) or go to a Family Planning Clinic or Sexual Health Clinic. The doctor will ask about your symptoms and sexual history to try and work out if bacterial vaginosis could be causing your symptoms.

If your doctor suspects BV, a vaginal examination and swab test may be recommended to test the vaginal discharge. This involves taking a small swab from the vagina and sending the swab to a laboratory for testing. The sample is examined under a microscope to look for ‘clue cells‘. These are vaginal cells that are covered with bacteria. The presence of clue cells is a sign of bacterial vaginosis.

To rule out the possibility that you have an STI, the sample may also be tested for the presence of different infections. It is possible to have BV and an STI at the same time.

The acidity of vaginal fluid may also be tested to help diagnose BV. The normal pH of vaginal fluid in women of childbearing age is around 4.5. If the pH of your vaginal fluid is higher than 4.5 (meaning it is less acidic than usual), it makes a diagnosis of bacterial vaginosis more likely. Your doctor can test the acidity of your vaginal fluid using pH paper.


In general, for a diagnosis of bacterial vaginosis to be made you need to have 3 of the following 4 criteria (called Amsel’s criteria):

  • thin white or grey vaginal discharge;
  • raised pH of vaginal fluid (pH more than 4.5);
  • an unpleasant (usually fishy) smell; and
  • vaginal swab test reveals the presence of clue cells.

What’s the difference between BV and thrush?

While thrush is more well known than bacterial vaginosis, BV is actually the more common cause of abnormal vaginal discharge. Neither thrush nor BV are considered to be STIs, and both can develop if you use personal care products that irritate the vagina. But there are several differences.

Vaginal thrush is caused by infection with a yeast called Candida, whereas BV is caused by an imbalance in bacteria in the vagina. If you have thrush, your discharge is usually thick and white (looks like cottage cheese) as opposed to thin and watery in BV. It may smell ‘yeasty’, not fishy. Also, in thrush there may be redness of the vulva and vagina (which is not usually seen in BV), and the itching and/or irritation is usually much more pronounced.

Your doctor can usually distinguish between these infections by taking a swab of vaginal fluid. The swab is sent to a lab for examination under a microscope to look for Candida yeast (seen in thrush) or clue cells (seen in BV). Testing the acidity of vaginal fluid can also help – the pH of the vagina is usually normal (pH 4.5) in women with thrush and high (less acidic) in women with BV.

Getting a proper diagnosis (rather than diagnosing yourself) is important to make sure you get the right treatment.

Bacterial vaginosis treatment

Antibiotics can be taken to treat bacterial vaginosis and relieve symptoms. Metronidazole, clindamycin or tinidazole are the antibiotics usually prescribed. Metronidazole and clindamycin can be given as a vaginal cream or gel, or as tablets to be taken by mouth.

Make sure you tell your doctor if you think you might be pregnant or are breast feeding, as this will affect the antibiotics they prescribe.

Taking your antibiotics

Take the full course of antibiotics (which is usually about a week’s worth) and let your doctor know if you have any reactions or side effects.

If you are taking metronidazole or tinidazole, you should not drink any alcohol during treatment and for several days after treatment is finished, as it can make you feel very unwell.

Some antibiotics given vaginally can interfere with the effectiveness of some condoms by weakening the latex – check with your doctor.

Can bacterial vaginosis get better on its own?

Sometimes BV does get better on its own. But if you have symptoms of BV, it’s best to be treated with antibiotics.

Self-care treatments that are being investigated for BV focus on improving the balance of good bacteria in the vagina. Taking probiotics or eating special types of yoghurt may help with this, but more evidence is needed to show that these measures help treat BV.

Why is it important to treat bacterial vaginosis?

For many women, having BV is seen as more of a nuisance than anything else. But it can sometimes be associated with serious complications, especially if you are pregnant or undergoing certain procedures.

Complications of bacterial vaginosis can include the following.

  • Infections following surgery that involves the genital tract, including termination of pregnancy (abortion) or insertion of an IUD. BV is associated with an increased risk of pelvic inflammatory disease (PID) – a serious infection of the reproductive organs (uterus, fallopian tubes and/or ovaries) that can result in permanent damage and even infertility.
  • Pregnancy complications, such as miscarriage, premature delivery and having a baby with a low birth weight.
  • Being more susceptible to catching sexually transmitted infections (STIs) such as genital herpes, chlamydia, HIV and gonorrhoea – the risk more than doubles if you have BV.
  • If you have HIV, the risk of passing it on to a male sex partner is increased.

Why does BV often come back?

Unfortunately, BV often comes back, even after treatment with antibiotics. This usually happens within 3 to 12 months of treatment.

Recurrent infections seem to be more common in women who have a regular sex partner, and recent research indicates that these recurrences may be linked to women being re-infected by their partners.

Research has also shown that the overgrowth of different types of bacteria in BV leads to the formation of what’s called a ‘polymicrobial biofilm’. This film sticks to the cells in the vagina and seems to protect the bacteria (to some degree, at least) from the body’s immune defences and from antibiotic treatment.

If you have a recurrence of BV, your doctor may prescribe antibiotic gel (such as metronidazole gel) that you apply to your vagina twice a week for 4-6 months.

Is it okay to have sex when I have BV?

Check with your doctor about whether it’s okay to have sex while you are being treated for BV.

If you have a female sex partner, it’s usually recommended that you avoid sexual contact until after you have been treated and your symptoms have gone.

There is currently no firm recommendation regarding sex with men during treatment for BV. It seems that you are more likely to re-infect yourself rather than infect a male partner if you do have sex when you have BV.

Should my partner be tested and treated for BV?

Testing and treating male sex partners is not currently routinely recommended. However, there is ongoing research into whether treating men may reduce the risk of recurrent infections in their female partners.

Testing and treating female sex partners is recommended.

How to prevent BV and stop it coming back

To help prevent BV or stop it coming back, avoid douching, which is not necessary as the vagina is self-cleaning. Douching can actually increase your chances of getting a vaginal infection. The best way to clean yourself is with a mild soap and water. Don’t force the water or soap into your vagina though – just use it on the outside. Avoid fragranced products and bubble bath.

Using condoms may reduce your chances of getting BV or having a recurrence. Women who have sex with men and consistently use condoms have been found to have lower rates of bacterial vaginosis. And, of course, practising safe sex by always using a condom is the best way to avoid STIs.

Using hormonal contraception (such as the oral contraceptive pill) may also help lower the risk of developing BV. Talk to your doctor about whether this would be a suitable option for you.