What STD is associated with BV?

Bacterial vaginosis (BV) is a common vaginal infection caused by an overgrowth of bacteria in the vagina. BV is associated with an imbalance in the vaginal microbiota, where healthy lactobacilli are replaced by a mixture of anaerobic bacteria. The most common STD associated with BV is trichomoniasis, caused by the protozoan parasite Trichomonas vaginalis. However, BV is also linked to increased transmission of other STDs like chlamydia, gonorrhea, and herpes simplex virus.

What is bacterial vaginosis?

Bacterial vaginosis is a dysbiosis of the vaginal microbiota characterized by a decrease in beneficial lactobacilli and an overgrowth of anaerobic bacteria like Gardnerella vaginalis, Atopobium vaginae, Mobiluncus species, Prevotella species, and others. The decrease in lactobacilli, which help maintain an acidic vaginal pH, leads to a rise in vaginal pH above 4.5. The shift in microbial composition and pH causes the signs and symptoms of BV.

Signs and symptoms

Many women with BV are asymptomatic. When present, signs and symptoms may include:

  • Thin, gray, homogeneous vaginal discharge
  • Fishy odor, especially after intercourse
  • Vaginal itching or irritation
  • Burning with urination

Causes and risk factors

Some factors that can increase a woman’s risk of developing BV include:

  • Having a new sex partner or multiple sex partners
  • Douching
  • Using an intrauterine device (IUD) for birth control
  • Lack of vaginal lactobacilli
  • Other infections like trichomoniasis

BV is associated with sex, but it is not considered a true sexually transmitted infection. Women who have never had sex can also get BV. The condition occurs when the delicate microbial balance in the vagina gets disrupted. However, sexual activity can increase BV risk by introducing new bacteria.

Trichomoniasis overview

Trichomoniasis is a common sexually transmitted disease caused by infection with Trichomonas vaginalis, a motile protozoan parasite. Trichomoniasis is primarily spread through sexual intercourse with an infected partner.

Signs and symptoms

Many people have mild or no trichomoniasis symptoms. When present, trichomoniasis signs and symptoms may include:

  • Green, yellow, or gray vaginal discharge
  • Vaginal itching and irritation
  • Painful urination or intercourse
  • Redness and swelling of the vulva
  • Frequent urination
  • Strong vaginal odor

Risk factors

Factors that increase the risk of getting trichomoniasis include:

  • Having a new sex partner or multiple partners
  • Not using condoms
  • History of STD
  • Exchange of sex for payment
  • Incarceration
  • Living in areas with high STD prevalence

The association between BV and trichomoniasis

There is a strong epidemiological association between bacterial vaginosis and infection with Trichomonas vaginalis. Women diagnosed with BV have been found to have trichomoniasis at rates from 10-50%, while 15-50% of women with trichomoniasis also have BV.

Some key points about the relationship between BV and trichomoniasis:

  • Trichomoniasis is considered a sexually transmitted infection, while BV is not – however, both conditions are associated with having new or multiple sex partners.
  • T. vaginalis infection is highly prevalent in women diagnosed with BV, suggesting it could be involved in triggering or exacerbating BV.
  • Women exposed to trichomoniasis have a 60% increased risk of developing BV.
  • T. vaginalis increases vaginal pH and causes microabrasions that may facilitate bacterial invasion and biofilm formation.
  • Disrupted vaginal microbiota and elevated pH from BV may increase susceptibility to acquiring T. vaginalis.
  • Treatment of trichomoniasis has been associated with BV resolution.

This interplay between vaginal bacteria associated with BV and T. vaginalis highlights the complex polymicrobial interactions in vaginal health.

Possible mechanisms linking trichomoniasis and BV

There are several mechanisms that may help explain the connection between trichomoniasis and BV:

  • Direct degradation of vaginal lactobacilli – T. vaginalis releases proteolytic enzymes that can damage and degrade lactobacilli.
  • Increased vaginal pH – Trichomoniasis raises vaginal pH, which can lead to loss of lactobacilli.
  • Biofilm formation – T.vaginalis may facilitate the formation of pathogenic bacterial biofilms on vaginal cells.
  • Inflammation – Chronic inflammatory response to T. vaginalis may contribute to BV acquisition.
  • Microabrasions – Surface damage to vaginal epithelium during T. vaginalis infection can expose binding sites for BV bacteria.
  • Bacterial transfer – T. vaginalis may carry and transfer vaginal bacteria like G. vaginalis directly during sexual intercourse.

Further research is needed to better understand the precise interactions between T. vaginalis, the vaginal microbiome, and bacterial vaginosis.

Diagnosing BV and trichomoniasis

Diagnostic testing is important for identifying both BV and trichomoniasis so that appropriate treatment can be provided.

BV diagnosis

BV is often diagnosed using Amsel criteria, which includes 3 of the following 4 findings:

  • Thin, homogenous discharge
  • Vaginal pH greater than 4.5
  • “Whiff test” positive
  • Clue cells visible on microscopy

Other diagnostic options for BV include:

  • Gram stain to evaluate vaginal discharge cell morphology and bacteria
  • DNA probe testing for high levels of G. vaginalis
  • Culture of vaginal fluid
  • Gas-liquid chromatography of vaginal fluid

Trichomoniasis diagnosis

Trichomoniasis is typically diagnosed through:

  • Microscopic examination of vaginal discharge – motile trichomonads may be visible
  • Culture of vaginal swab
  • Nucleic acid amplification test (NAAT) of urine or vaginal swab
  • Rapid antigen testing

Multiple testing modalities may be used because trichomoniasis can be intermittent or challenging to detect.

Concurrent STI testing for chlamydia and gonorrhea should also be performed given the overlap in risk factors and exposures.

Complications of trichomoniasis and BV

When left untreated, both trichomoniasis and bacterial vaginosis can lead to significant complications and adverse health outcomes.

Complications of trichomoniasis

Complications of trichomoniasis may include:

  • Increased transmission of HIV
  • Pelvic inflammatory disease
  • Infertility
  • Preterm delivery
  • Low birth weight infants
  • Increased risk of cervical cancer

Complications of BV

Bacterial vaginosis has been associated with the following risks:

  • Preterm labor and delivery
  • Postpartum endometritis
  • Pelvic inflammatory disease
  • Increased susceptibility to HIV and other STDs
  • Post-surgical infections
  • Pregnancy complications

Prompt diagnosis and treatment of both trichomoniasis and BV is important to avoid adverse outcomes. Screening high-risk individuals can allow for early detection and intervention.

Treatment options

BV and trichomoniasis are treatable conditions, but recurrence or reinfection is common.

BV treatment

First line treatments for BV include:

  • Metronidazole 500 mg orally twice daily for 7 days
  • Metronidazole gel intravaginally once daily for 5 days
  • Clindamycin cream intravaginally at bedtime for 7 days

Alternative regimens may include oral clindamycin or tinidazole. Sexual partners generally do not need treatment.

Trichomoniasis treatment

Trichomoniasis is treated through single-dose oral medication:

  • Metronidazole 2 g or tinidazole 2 g orally in a single dose
  • Can be taken with or without food
  • Sexual partners should be treated simultaneously to prevent reinfection
  • Avoid alcohol during treatment and for 24 hours after taking metronidazole or 72 hours after tinidazole

Recurrence prevention

The following can help prevent recurring BV or trichomoniasis after treatment:

  • Completing the full antibiotic course as prescribed
  • Abstaining from intercourse until treatment is complete
  • Using condoms or dental dams to reduce exchange of fluids
  • Avoiding douching which can disrupt vaginal flora
  • Retesting several weeks after treatment
  • Ensuring infected sexual partners are also treated

For recurrent BV, maintenance therapy with oral or vaginal metronidazole may be considered. Maintaining vaginal health through proper hygiene and probiotics may also be beneficial.

Public health impact

Due to the prevalence of bacterial vaginosis and its association with trichomoniasis infection, these conditions have a significant public health impact.


Some key statistics on BV and trichomoniasis epidemiology:

  • BV is the most common vaginal condition in women ages 15-44.
  • BV prevalence is around 29% for women 14-49 years old in the US.
  • An estimated 3.1 million women in the US have BV.
  • Trichomoniasis is the most common curable STD with an estimated 3.7 million cases among women and men.
  • 3.1% of women ages 14-49 have trichomoniasis in the US.
  • Black women have higher rates of both trichomoniasis and BV.

Financial burden

The CDC estimates that treating BV and its complications costs more than $1 billion annually in the US. Direct medical costs for trichomoniasis are estimated at $24 million per year. These conditions also lead to lost wages due to illness. Improved screening, diagnosis, and treatment could reduce this financial burden.

Prevention opportunities

Public health initiatives focused on education, condom promotion, partner treatment, and improved hygiene could help lower rates of BV and trichomoniasis. Developing more effective treatments or a vaccine for T. vaginalis could also have a major preventive impact. Ongoing research in this area is needed.


In summary, bacterial vaginosis has a strong epidemiologic association with trichomoniasis, the most common curable sexually transmitted infection. The interrelationship between BV-associated bacteria like G. vaginalis and T. vaginalis infection highlights the complex vaginal microbiome dynamics.

Trichomoniasis likely contributes to initiating or worsening BV in some women through mechanisms like direct lactobacilli degradation, biofilm formation, increased pH, and inflammation. In turn, the vaginal dysbiosis of BV may facilitate T. vaginalis acquisition and colonization.

Diagnosing and treating both trichomoniasis and BV in affected women and their partners can help reduce reproductive complications. Further research on vaginal health could lead to better therapeutic and preventive solutions for these extremely common conditions that impact millions of women.

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