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Vaginitis is one of the most common medical problems for which women seek healthcare. This condition is defined as an infection or inflammation of the vagina and can cause discharge, itching and pain. The most common causes of vaginitis include bacteria (around 40-50% of cases), Candida, or Trichomonas vaginalis [1, 2]. Despite its high incidence, the pathogenesis of bacterial vaginosis (BV) remains poorly understood. Although, it is generally not considered to be a sexually transmitted infection (STI), bacterial vaginosis can increase the risk of contracting certain STIs.
Bacterial vaginosis is vaginitis that results from a bacterial source [1]. It is very common with prevalence ranging from 20 to 60% depending on the geographical region [3]. The highest prevalence is found in Sub-Saharan Africa, and the lowest in Asia, Western Europe and Australia, while 30% of women in the US are affected [4].
BV was first described in 1955, and despite 65 years of research the cause of BV is not fully understood [3].The current hypothesis is that BV is caused by an overgrowth of opportunistic bacteria which results in a decrease in the levels of Lactobacilli. In a healthy vaginal flora about 90-95% of the total bacteria are Lactobacilli. In many cases of BV anaerobic bacteria, usually gram-positive cocci and gram-negative bacilli, become the dominant bacteria. Commonly found bacteria include Prevotella species, Gardnerella vaginalis and Mobiluncus species [3]. Recurrent BV can occur after treatment.
Several studies have shown a lower rate on recurrent BV among women who use condoms or abstain from sex as compared to women who have unprotected sex, suggesting that the infection is transmitted between partners [3]. However, other studies highlighted the lack of evidence that partner therapy can reduce the rate of BV recurrence suggesting that reinfection may not be the cause of recurrent BV [3].
The vaginal microbiota is instrumental in female reproductive health and maintaining a healthy environment. A healthy vaginal microbiome is Lactobacilli dominant. Many of the bacterial species associated with the vaginal microbiome are difficult to culture in the lab [5].
The early research that was done to define the vaginal microbiome was done using traditional culture methods. The use of molecular techniques such as PCR and WGS have enabled the identification of multiple additional bacteria such as Atopobium vaginae, Megasphaera, Eggerthella-like uncultured bacteria, and three newly described members of the Clostridiales order that have high specificity for BV which has increased our understanding of the vaginal microbiome [5].
In a healthy vaginal microbiome, the flora is stable and prevents the colonization by other pathogens thus preventing infections [5]. Lactobacilli are dominant in a healthy biome and produce antimicrobial compounds such as hydrogen peroxide, lactic acid, bacteriocins, and arginine deaminase enzyme all of which prevent the growth of pathogenic bacteria [5]. Studies are ongoing to further understand and define the vaginal microbiome, current research has shown a large microbiome diversity in women who are asymptomatic for BV including some that are not Lactobacilli dominant [5]. Longitudinal studies also show a great deal of rapid fluctuation on the composition of the bacterial flora in individual women over time [5].
There are multiple risk factors associated with BV, though the exact contribution of each is not fully understood. Women who are sexually active, especially those with multiple partners or a new sexual partner, have an increased likelihood of developing BV [2, 3]. The spread of bacteria among individuals through sexual intercourse may alter the natural balance of bacterial flora within the vagina, and this imbalance appears to lead to the development of bacterial vaginosis [6]. Mechanical or chemical interaction associated with sexual activity such as contact with highly alkaline semen may play a role in the development of BV [2].
In addition, rinsing the vagina with water or other cleansing agents disrupts the natural balance of beneficial bacteria in the vaginal ecosystem and this disruption can create an environment conducive to the overgrowth of harmful bacteria, leading to BV [3]. Antibiotic use also may inadvertently eliminate beneficial bacteria, upsetting the delicate balance in the vagina and promoting BV [4].
Some studies suggest a link between the use of intrauterine devices (IUDs) and an increased risk of BV; the reasons for this association are not yet fully understood but may be due to changes in the vaginal environment caused by the presence of the IUD [3]. Other studies have shown that combined use of progestin only oral contraceptives, and condoms may decrease the risk of contracting BV [3]. Elevated estrogen levels, for example, can create conditions more favorable for BV development [3].
Immunocompromise conditions such as HIV, diabetes, or autoimmune disorders also can increase the risk [7]. Some studies have shown that certain racial and ethnic groups may have a higher susceptibility to BV. For instance, women of African descent appear to have a higher risk compared to women of other ethnic backgrounds [3]. Research has shown variation in the vaginal microbiota of asymptomatic women in the same geographical area and have identified differences based on ethnicity [2].
A hallmark symptom of BV is an abnormal vaginal discharge, the discharge is typically thin, grayish-white, and has a distinctive foul or fishy odor and more noticeable after sexual intercourse or during menstruation [1]. Some women may experience vaginal itching and irritation but it is rare [1].
Unlike other vaginal infections, such as yeast infections or sexually transmitted infections (STIs), bacterial vaginosis typically does not cause significant redness, swelling, or pain in the genital area so this can make it challenging for women to self-diagnose BV based solely on symptoms, highlighting the importance of seeking professional medical advice [1].
Surprisingly, a significant proportion of women with BV may not exhibit any noticeable symptoms at all. However, asymptomatic BV still increases the risk of complications, such as pelvic inflammatory disease (PID) and preterm birth in pregnant women [1].
The diagnosis of bacterial vaginosis involves a combination of clinical symptoms, physical examination, and laboratory tests. The clinical presentation may be difficult to differentiate BV from other diseases such as Trichomoniasis, Candida vulvovaginitis, and aerobic vaginitis [1]. It is important to note that some women with BV may be asymptomatic, making diagnosis more challenging, so laboratory testing plays a key role in the diagnosis.
The Nugent score is considered the gold standard for the diagnosis of BV. It involves collecting and Gram staining vaginal secretions followed by a microscopic exam. A score is given based on the relative quantity of organisms observed; Lactobacillus will appear as large Gram-positive rods, Gardnerella as small Gram-variable rods, and Mobiluncus as curved Gram-variable rods. Higher scores are consistent with BV [8]. One limitation of the Nugent score is it does not take into account other newly identified bacteria that are highly associated with BV and does not rate the severity of the BV [8]. The test requires a skilled operator and there can be person to person variation while interpreting the same test.
Amsel clinical criteria is often used at the point of care by the treating clinicians to diagnose BV. It evaluates the characteristics of the vaginal discharge, the vaginal pH, odor of the discharge (whiff test), and the presence of clue cells on microscopy [8]. However, these criteria have limitations, such as subjectivity and the need for skilled personnel [8].
Molecular diagnostics tests for BV such as direct probe assay, NAATs, and sequencing have advantages over the traditional methods [8]. They can identify fastidious bacteria associated with BV that culture methods were unable to identify [8]. Molecular tests are also less subjective than the Nugent test or Amsel criteria.
It is important to differentiate BV from other vaginal infections like yeast infections or STIs, especially since the treatment approaches vary significantly. This may be difficult as the clinical presentation has many overlapping symptoms, and a definitive diagnosis may be difficult to make without laboratory testing. Proper diagnosis and treatment of BV are essential to alleviate symptoms and prevent potential complications. Therefore, if any symptoms of BV are present, or if there are concerns about vaginal health, it is crucial to seek medical attention for accurate diagnosis and appropriate management.
Although up to 30% of bacterial vaginosis cases may resolve without treatment, this condition should be treated with either clindamycin or metronidazole [4].
Treatment is only recommended for symptomatic women, according to the United States (US) Centers for Disease Control and Prevention (CDC) treatment guidelines, due to a lack of definitive evidence to support treatment of asymptomatic women [3]. Though there is some data that suggests that treatment of asymptomatic BV may reduce the risk of BV associated adverse sequelae [3]. Because BV increases a woman’s risk of getting HIV and other STIs, the CDC recommends STI and HIV testing for any woman with BV [9].
BV is associated with adverse outcomes. Numerous studies have established a strong association between BV and pelvic inflammatory disease (PID), a serious infection affecting the female reproductive organs. The dysbiotic vaginal environment in BV facilitates the ascension of pathogenic bacteria into the upper genital tract, leading to inflammation and potential scarring of the fallopian tubes, which can result in infertility and ectopic pregnancies [2]. Moreover, untreated BV may increase the risk of endometritis, postoperative infections following gynecological procedures, and complications associated with assisted reproductive techniques [2].
BV has been associated with the acquisition and transmission of various STIs [3]. The increased susceptibility to STIs, may be attributed to the altered vaginal microenvironment. BV-related changes in pH and vaginal flora compromise the natural protective barrier against pathogens, making women more susceptible to STI acquisition and potentially promoting viral shedding [10].
One of the most concerning adverse sequelae of BV is its association with adverse pregnancy outcomes. Around 10-30% of pregnant women with BV have a preterm delivery, which can increase perinatal mortality by as much as 70% [2]. Additionally, there is an increased risk for late miscarriage, preterm rupture of the membranes, intrauterine infections, and postpartum infections [2].
Beyond the physical health implications, BV can significantly impact the quality of life for affected women. The recurrent nature of BV can lead to chronic discomfort, recurring symptoms, and psychological distress. The stigma and embarrassment associated with BV may hinder women from seeking timely medical attention, perpetuating the cycle of recurrent infections.
An STI is caused by a source that is not endogenous to the vaginal flora. Since bacterial vaginosis is caused by an overgrowth of normal vaginal bacteria, it does not meet the definition of an STI [6] [2]. Current literature suggests that BV is related to sexual activity [3]. Furthermore, while rare, bacterial vaginosis can be present in patients who have never had sexual intercourse [4]. Therefore, while BV is not an STI, it does have some characteristics of an STI [2].
The NIH Longitudinal Study of Vaginal Flora (LSVF) investigated the link between BV and STIs. They found that BV results in a 1.5- to 2-fold risk of developing chlamydia, gonorrhea, and trichomonas [5]. The study also showed that the risk of developing an STI increases with the severity of the BV (as defined by Nugent score) [5, 11].
Another study showed that women with asymptomatic BV who were treated with antibiotics had a lower risk of developing an STI than asymptomatic women who were not treated [5]. It is believed that STI pathogens are more easily able to cause infection due to the low pH and decreased production of lactic acid associated with BV [5]. Several studies have also shown that BV-associated pathogens can increase HIV shedding and increase the risk of transmission of HIV by women with BV [5].
Despite the prevalence, the cause, risk factors, and complications of BV are not well understood. BV is understood to result from a change in the vaginal flora, from a Lactobacilli-dominant environment to one dominated by opportunistic anaerobes. Our understanding of the vaginal microbiome is largely based on traditional laboratory testing methods such as culture and Gram stain. Only a small percentage of bacteria present in the vaginal microbiome are able to be identified by these methods, which has previously limited our understanding of the disease [12].
As molecular testing methods become more widespread, our knowledge is increasing. Sequencing allows for identification of all organisms present, and NAAT is useful in detecting these known organisms. Through studies using molecular testing, we have learned there is a great deal of heterogeneity in the vaginal microbiome. We have learned that some women have a non-lactobacilli dominant microbiome yet are asymptomatic for BV and frequent changes in the microbiome have been observed [12]. NAAT testing also allows for the simultaneous detection of many STIs as is recommended by the CDC. As further research is conducted our understanding of the disease will grow which will result in improved health for women.
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