Can BV Cause A Positive Chlamydia Test?

No: bacterial vaginosis (BV) does not cause a positive chlamydia test. The test used in the UK detects the genetic material of Chlamydia trachomatis itself, and the bacteria that overgrow in BV are not picked up by it, so a positive result means chlamydia was found. The two are connected, but the other way round: BV, and the loss of the protective lactobacilli that comes with it, makes chlamydia easier to catch if you are exposed to it.^{1, 2} The condition itself is explained in what is the main cause of BV.

Can BV cause a false positive chlamydia test?

Not in any documented way. Chlamydia tests (NAATs, or nucleic acid amplification tests) work by detecting genetic material from the bacterium Chlamydia trachomatis in a urine or swab sample. The NAAT tests used in the UK detect chlamydia's own genetic material, not the mixed bacteria of BV, so the shift in vaginal bacteria that BV causes is not what the test looks for.

False positives do happen, rarely, and their causes are practical rather than biological:

• Lab handling errors or a contaminated sample
• Leftover chlamydia DNA in the weeks after a course of antibiotics, because the test can detect fragments after the bacteria are dead
• Testing for cure too soon after finishing antibiotics, for the same reason
• Not following the self-test kit instructions correctly

If you think your result doesn't add up, the standard advice from sexual health clinics is to ask for a repeat test, ideally using a different sample type or method, before starting to worry unnecessarily.

So is BV actually linked to chlamydia, or is it a coincidence?

A 2003 study of 255 women who had recently had sex with a partner with urethritis found that those with bacterial vaginosis were 3.4 times as likely to test positive for chlamydia and 4.1 times as likely for gonorrhoea as women with normal vaginal flora, and that women carrying protective lactobacilli were less likely to be infected.² A 2023 systematic review of sequencing studies went further into which bacteria matter: women whose vaginal community was dominated by Lactobacillus iners, a less protective species, had 3.4 times the odds of chlamydia compared with women dominated by Lactobacillus crispatus, and 2.1 times the prevalence of BV, although that second estimate was not statistically significant (confidence interval 0.9 to 4.9).¹ The picture that emerges is of a vaginal environment, rather than a single bacterium, that makes chlamydia easier to acquire.

That doesn't mean BV causes chlamydia directly. BV is an overgrowth of the bacteria already living in your vagina, most often triggered by a period, a new sexual partner, douching, perfumed products or a copper coil, and it isn't classified as a sexually transmitted infection (we've gone into more detail on who's most likely to get BV in a separate post). Chlamydia trachomatis, on the other hand, is passed on through vaginal, anal or oral sex. What the research and the NHS describe is a vagina made less acidic, with fewer of the protective lactobacilli that normally keep harmful bacteria in check.³ That leaves you more vulnerable to catching an STI like chlamydia if you're exposed to it, not that BV magically converts into one.

Does having BV mean you have chlamydia?

No. BV and chlamydia are separate conditions with separate causes, and having one doesn't confirm you have the other. That said, they're commonly confused because their symptoms can overlap, both are extremely common, and both often show no symptoms at all.

Here's a quick side by side:

Bacterial vaginosis:

• Not sexually transmitted, though sex can trigger it
• Caused by an imbalance in your existing vaginal bacteria
• Classic sign is a thin, greyish-white discharge with a strong fishy smell, especially after sex
• Usually doesn't cause soreness or itching
• About half of women with BV have no symptoms at all

Chlamydia:

• A sexually transmitted infection caused by Chlamydia trachomatis
• Passed on through unprotected vaginal, anal or oral sex
• Can cause unusual discharge, bleeding between periods or after sex, and a burning sensation when you pee
• Most people, women and men alike, have no symptoms at all

Because the symptom pictures overlap so much, and because BV can occur at the same time as an STI, a clinician will usually test for both when you go in with unusual discharge or discomfort. That's the only way to know for certain which one (or both) you're dealing with. We've unpacked this confusion in more depth in Can BV mean STD? if you'd like the fuller picture.

Can BV turn into chlamydia if it's left untreated?

No. BV cannot transform into chlamydia, no matter how long it goes untreated. They're caused by entirely different organisms, and one doesn't evolve into the other. What untreated BV does do is raise your risk of picking up chlamydia or gonorrhoea if you're exposed to them, and the NHS says BV increases the risk of getting an STI, possibly because it makes the vagina less acidic and reduces its natural defences.^{2, 3} If you are sexually active while you have BV, especially without a condom, your odds of picking up an STI go up: not transformation, but increased susceptibility.

Left untreated, BV itself can also lead to its own complications, particularly in pregnancy, where the NHS says there is a small chance of premature birth or miscarriage.³ For the fuller list of what untreated BV can lead to, and how long it tends to linger if you leave it, see What does untreated BV lead to? and What Happens If You Leave BV Too Long?

Can you have BV and chlamydia at the same time?

Yes, and it happens often enough that clinics routinely screen for both together. Since BV increases your vulnerability to chlamydia, and both conditions frequently cause no obvious symptoms, plenty of people are dealing with both without realising it. If you're diagnosed with one, it's worth asking to be tested for the other, and for STIs generally, rather than assuming a single diagnosis tells the whole story.

Treatment for the two doesn't overlap. BV is treated with antibiotic tablets, gels or creams, most often metronidazole, while chlamydia needs its own course of a different antibiotic. Having both at once just means you'll need both courses, and you'll usually be advised to avoid sex until you and any partner have finished treatment and tested clear. The UK treatment page covers the BV side.

What can make a chlamydia test falsely positive?

BV is not a documented cause. The documented ones are recent treatment (leftover bacterial DNA can be picked up by sensitive NAAT tests for a short period after a successful course), sample contamination during collection or lab processing, and a self-test kit used outside its instructions. A test can also miss chlamydia if it is taken from a site that was not swabbed, which is why the NHS says a swab from the bottom, throat or eyes may be needed when those areas are affected; a positive result should be taken seriously rather than dismissed.⁴

Getting tested in the UK

If you're in the UK, testing for both BV and chlamydia is straightforward and often free. Sexual health clinics offer walk-in testing for both without a referral, GPs can test for BV, as how BV itself is tested explains, and free NHS chlamydia self-test kits are available through some pharmacies and sexual health clinics, with free postal kits specifically for under-25s.⁴ Some pharmacies also sell self-test kits if you'd rather test privately. Whichever route you take, if you get a positive result for either infection, your recent sexual partners will need to be tested too, since chlamydia in particular is easily passed on without either person realising.⁴ Pelvic pain, fever, or bleeding between periods or after sex are not BV symptoms: see a GP or sexual health clinic, or call NHS 111, rather than wait.

Frequently asked questions

Why did I test positive for chlamydia when my partner tested negative?

It isn't proof that someone's been unfaithful. Timing matters: the NHS says chlamydia symptoms can start from a week to several months after infection, and a test taken very soon after exposure can miss an early infection, so partners tested at different points can get different results.⁴ Not all tests are equally sensitive, and a low bacterial load can be missed. Chlamydia can also sit in the throat or rectum, areas that aren't always swabbed in a standard test, so a negative genital result doesn't always mean a person is infection-free. Reinfection or a new exposure is possible too, but it's one of several explanations, not the default assumption. Both partners retesting, including at additional sites if relevant, is a more useful next step than jumping to conclusions.

What are the signs of chlamydia to watch for?

Most people with chlamydia have no symptoms whatsoever, which is exactly why regular testing matters more than waiting for warning signs. When symptoms do show up, they typically include unusual vaginal discharge, or discharge from the penis that's white, cloudy or watery; a burning sensation when peeing; pain in the lower abdomen in women; bleeding between periods or after sex; and pain or swelling in the testicles in men.⁴ Left untreated, chlamydia can lead to pelvic inflammatory disease, infertility, ectopic pregnancy and reactive arthritis, so it's not an infection to sit on even though a course of antibiotics clears it.

Can you get rid of BV for good?

BV comes back in more than half of women within a year of treatment, and the full recurrence plan, including the 2025 partner trial and what the NHS offers after four episodes a year, is on why do I keep getting BV.⁵

Sources

1. Carter KA, et al. Epidemiologic evidence on the role of Lactobacillus iners in sexually transmitted infections and bacterial vaginosis: a systematic review and meta-analysis. Sexually Transmitted Diseases, 2023. PubMed 36729966.
2. Wiesenfeld HC, et al. Bacterial vaginosis is a strong predictor of Neisseria gonorrhoeae and Chlamydia trachomatis infection. Clinical Infectious Diseases, 2003. PubMed 12594649.
3. NHS. Bacterial vaginosis. nhs.uk/conditions/bacterial-vaginosis.
4. NHS. Chlamydia. nhs.uk/conditions/chlamydia.
5. Bradshaw CS, et al. High recurrence rates of bacterial vaginosis over the course of 12 months after oral metronidazole therapy and factors associated with recurrence. Journal of Infectious Diseases, 2006. PubMed 16652274.