A common vaginal condition known as bacterial vaginosis (BV) may actually be a sexually transmitted infection (STI), according to researchers.

The NHS currently says BV is caused by "a change in the natural balance of bacteria in your vagina and is not an STI", even though it can be triggered by sex.

However, a study claims BV - which affects nearly a third of women worldwide and can lead to infertility, premature births and newborn deaths - is spread during intercourse and fits the definition of an STI.

The Australian trial, published in the New England Journal of Medicine, found treating sexual partners, not just the patient, can be vital to clear the infection.

What is BV?

BV is a common cause of unusual vaginal discharge that has a strong fishy smell.

The colour and consistency may change too, such as becoming greyish-white as well as thin and watery.

Half of women with bacterial vaginosis do not have any symptoms though.

Bacterial vaginosis does not usually cause any soreness or itching.

It can be treated with antibiotic tablets or gels or creams.

In the trial of 164 couples with BV, the researchers achieved higher cure rates by treating BV as an STI, with both sexual partners - rather than just the woman - given antibiotics.

The doctors stopped the study early when it became clear that BV recurrence was halved using this approach.

One of the lead researchers, Prof Catriona Bradshaw, said: "Our trial has shown that reinfection from partners is causing a lot of the BV recurrence women experience, and provides evidence that BV is in fact an STI.

"Part of the difficulty in establishing whether BV is sexually transmitted has been that we still don't know precisely which bacteria are the cause, but advances in genomic sequencing are helping us close in on that mystery," she added.

In the study, run by Monash University and Alfred Health researchers at the Melbourne Sexual Health Centre, half of the men got an oral antibiotic and a topical antibiotic cream to apply to the skin for one week, while the control group of men were given no treatment.

Given the findings, the clinic has now changed its clinical practice to routinely treat both partners.

The British Association for Sexual Health and HIV said the findings provided "valuable evidence supporting what has long been suspected – that BV-associated bacteria may be sexually transmitted, particularly in those who experience recurrent infections".

"This research enhances our understanding of BV and offers promising insights that may help to guide treatment approaches in more persistent cases," said a spokesperson.

If you have symptoms of an STI or concerns about BV, visit your doctor or local sexual health clinic.