EVALUATING BACTERIAL VAGINOSIS USING THE NUGENT SCORING SYSTEM

EVALUATING BACTERIAL VAGINOSIS USING THE NUGENT SCORING SYSTEM

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ABSTRACT

BACKGROUND AND OBJECTIVE: Bacterial vaginosis is the most common form of vaginal infection in women of reproductive age.  It is a condition with diverse etiology and an important cause of morbidity in women of reproductive age. This study was carried out to determine the accuracy of using the Nugent scoring system as a means of diagnosing Bacterial vaginosis.

MATERIALS AND METHOD: The prospective study was conducted in Benin City, Edo state between July and September 2012 and included 67 women between the ages of 16 and 45 years. Specimens collected from the lateral wall of the vagina were subjected to Gram staining and the microscopic slides examined and the different morphotypes of bacteria quantified using the Nugent scoring system.

RESULTS: The age range was 16-45 years with a mean of 24.9 years. BV was diagnosed by the Nugent method in 13.4% of women with the highest prevalence found in the age group of 16-20 years. The relationship of a positive whiff test, presence of clue cells and a pH>4.5 with bacterial vaginosis was shown to be highly significant (p=0.0051, P=0.001, P=0.0077).

CONCLUSION: Nugent scoring system appears to be a reliable and convenient method for laboratory evaluation of cases of bacterial vaginosis.

KEYWORDS: Bacterial Vaginosis, Nugent’s score, Gram staining.

CHAPTER ONE

INTRODUCTION

Vaginal bacteria communities are composed of mixtures of diverse species and the relative abundance of these species in part determine urogenital health and disease in women. It is generally acknowledged that vaginal bacterial communities predominated by Lactobacillus species are normal and healthy while communities predominated by other genera such as Gardnerella vaginalis are abnormal and unhealthy. This latter condition essentially describes a poorly understood syndrome known as Bacterial Vaginosis (BV).

   The composition of vaginal flora is the focus of interest of recent investigation because of its importance to women’s reproductive organ and general health (Patta et al, 2008). The condition is although common but under diagnosed. This may be due to confusion over its microbial origin (O’Dowd et al., 1996). The vagina is a dynamic ecosystem that is balanced due to the interaction of factors of the native bacterial biota. In healthy adult women, the normal vaginal pH is < 4.5. The predominant species of lactobacilli maintain a low pH through their fermenting activity which protects the area against the invasion of undesirable microorganisms (Pascual et al., 2006). The acidic medium produced by Lactobacilli suppresses the growth of other microorganisms (Klebanoff et al., 1991).  Clinically, malodorous vaginal discharge, especially a fishy odour is the most common symptom (Fluery, 1981). Various studies have found the prevalence of BV to range from 15 to 30 per cent in non pregnant women and up to 50 per cent in pregnant women (Nelson and Macones, 2002). Clinical studies have demonstrated an association of BV with adverse pregnancy outcomes, upper genital tract infections such as pelvic inflammatory disease, endometritis, post-gynaecologic surgery infections, cervicitis, urinary tract infections, cervical intraepithelial neoplasia, and increased risk of sexual acquisition of human immunodeficiency virus infection (Lanzafame, 2002). Given its high prevalence and association with obstetrical and gynaecological complications, detection of this entity in women is of paramount importance. Studies using cultivation methods have shown that women with bacterial vaginosis have loss of vaginal lactobacilli and concomitant overgrowth of anaerobic and facultative bacteria. Several bacteria have been implicated in bacterial vaginosis, such as Gardnerella vaginalis (Gardner and Duke, 1955) and Mobiluncus curtisii (Spiegel et al., 1983) but these species are also found in subjects who do not have bacterial vaginosis and thus are not specific markers for the disease (Spiegel, 1991). For this reason, bacterial cultivation of vaginal fluid has not proved useful for the diagnosis of bacterial vaginosis. Rather, clinical criteria or Gram’s staining of vaginal fluid is used for diagnosis. The clinical criteria of diagnosing BV is confirmed using the composite criteria described by Amsel et al in 2002 in which 3 or 4 of the following have to be present for diagnosis;

 (1) A thin homogenous discharge.

(2) Elevated vaginal pH above 4.5

 (3) Release of amines on addition of 10 percent potassium hydroxide solution to vaginal fluid.

(4) The presence of clue cells on wet mount.

 However, Amsel criteria may not be adequate to diagnose patients, as approximately 50 percent of BV patients may be asymptomatic (Gregor et al., 2002). Further, there exists a continuum from normal lactobacillus dominated flora through “to severe BV” with an intermediate category which the Amsel criteria fail to recognize. Thus, grading the microbial flora seen in Gram-stained vaginal smears, especially the scoring criteria proposed by Nugent et al in 1991, as an alternative method has become useful as a diagnostic tool. In this system, large Gram-positive rods (Lactobacillus morphotypes), small Gram-negative to Gram-variable rods (Gardneralla vaginalis and Bacteroides morphotypes) and curved Gram negative rods (Mobiluncus species) are quantitated and a summation score is obtained. BV is not a new clinical condition rather it is an infection that is under recognized and misdiagnosed in developing countries including Nigeria. Due to this under recognition, most clinicians do not even recognize BV diagnosis as a routine laboratory investigation for females of child bearing age. This study was carried out to determine the accuracy of using the Nugent scoring system as a means of diagnosing BV.

CHAPTER TWO

LITERATURE REVIEW

                       Bacterial vaginosis (BV) is a disorder of the vaginal ecosystem characterized by a change in the vaginal flora from the normally predominant lactobacillus to one dominated by sialidase-enzyme-producing organisms including Gardnerella vaginalis, Mobiluncus spp., Prevotella bivia, Bacteroides spp., Peptostreptococcus spp., Ureaplasma urealyticum, and Mycoplasma hominis (Hills, 1993). Several studies have linked BV to an increased risk of acquisition of sexually transmitted diseases (STDs) and human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) (Sewankambo et al., 1997, Taha et al., 1998) as well as a number of gynaecological complications (Faro et al., 1993). BV is a disordering of the chemical and biological balance of the normal flora. Lactobacillus species are the predominant bacteria in normal vaginal flora constituting the greatest percentage of total vaginal flora. Lactobacilli species present in the vaginal flora decreases vaginal pH by producing lactic acid and thus mediate the first line of protection against vaginal infection. In addition, hydrogen peroxide production by some lactobacillus species has been found to suppress the growth of many microbial organisms (Dickson et al., 2006).

           BV is the most common cause of abnormal vaginal discharge in adult women. The prevalence of BV ranged between 10-30% in different population all over the world (Morws et al., 2001). Several investigations have been performed to identify one or several bacteria comprising the decisive pathogenic factor in the syndrome, but so far no specific bacteria have been implicated in causing BV. Rather, it seems that all these organisms may play a synergistic role in producing the symptoms of BV. The condition is although common especially in low settings but under diagnosed. This may be due to confusion over its complex polymicrobial nature (Hillier et al., 1992).

             BV as a specific entity has been recognized since the 1950s and is characterized by an increased malodorous discharge. It is associated with marked changes in vaginal flora often described as a change in local vaginal ecology and a notable absence of inflammation, a reduction in LB species and an increase in Gardnerella vaginalis. Several anaerobic species including mobiluncus spp, Prevotella species and others such as Mycoplasma hominis have been described. The stimuli for these changes are very poorly understood. BV is common and recent works have heightened the importance of its recognition. The two most widely accepted methods for the diagnosis of bacterial vaginosis, Amsel’s composite criteria (Amsel et al., 1983) and Nugent’s Gram stain evaluation of bacterial morphotypes (Nugent et al., 1991) are not used sufficiently in routine practice (Langsford et al., 2001), mostly in low income countries. Although the diagnosis of BV by Amsel’s criteria is simple, it is relatively insensitive and not easily subjected to quality control, and the apparent complexity of the latter may have limited its routine application by clinical laboratories.

MICROBIOLOGY OF BV

           Normal vaginal flora consist of both aerobic and anaerobic bacteria with Lactobacillus species being the predominant bacteria and accounting for greater than 95% of all bacteria present (Spiegel et al., 1980). Lactobacillus species are believed to provide defence against infection in part by maintaining an acid pH in the vagina and ensuring H2O2 is present in the genital environment. In contrast, BV is a polymicrobial syndrome resulting in a decreased concentration of Lactobacilli and an increase in pathogenic bacteria mainly anaerobes or microaerophilles. Gardnerella vaginalis is one of the main bacteria found in BV, but this can also be found on culture in approximately 50% of healthy women. Other organisms commonly associated with BV are Prevotella species, Mycoplasma hominis, and Mobiluncus species (Hillier, 1993). Overgrowth of these anaerobic organisms can cause an increase in pH from less than 4.5 to up to 7.0 [DTB, 1998; CEG, 2001].

PREVALENCE OF BV

    BV is a common gynaecological condition, reported in 5–51% of women, depending on demographics and whether or not they are symptomatic (Mead, 1993). Bacterial vaginosis (BV) is the most common infective cause of vaginal infection. It is about twice as common as candidiasis (Joesoef and Schmid, 2005). The prevalence of BV is variable. About 14.2% of Nigerian women are affected by BV (Anukam et al., 2006). Various studies have found the prevalence of BV to range from 15 to 30 per cent in non pregnant women and up to 50 per cent in pregnant women (Nelson and Macones, 2002). In the united state, prevalence has been reported as 9% for general practice populations, 12% for women attending ante natal clinic and 28% for women attending termination of pregnancy clinics [HPA, 2002]. The prevalence of BV varies by race and ethnicity from 6% in Asians and 9% in whites to 16% in Hispanics and 23% in African Americans (Anderson et al., 1992).  

FIG 1: COMPARING THE PREVALENCE OF BV AND OTHER VAGINAL INFECTIONS. (Andrea and Chaplain, 2011).

CA- Candida BV- Bacterial vaginosis TV- Trichomonas vaginalis CT-Chlamydia tracomatis GC- Gonococci

PREDISPOSING FACTORS TO BACTERIAL VAGINOSIS

The natural history of BV is unclear, as are the risk factors for its acquisition. It is not thought to be sexually transmitted as no causative microorganism has been found to be transmitted between partners. It can arise and remit spontaneously in sexually active and non-sexually active women [DTB, 1998; CEG, 2001; Joesoef and Schmid, 2005].Race has been identified as one potential risk factor as blacks have higher rates than whites (Morris et al., 2001, Goldenberg et al., 1996). It is unclear, however, if this discrepancy is due to racial differences in vaginal microbiology (Newton et al., 2001) or culturally mediated differences in vaginal-cleansing behaviours such as douching (Holzman et al., 2001). Other activities or behavior that can upset the normal balance of bacteria in the vagina and put a woman at increased risk include;

Multiple sex partners or a new sex partner: Data regarding the association between sexual activity and BV acquisition are contradictory. The link between sexual activity and bacterial vaginosis isn't entirely clear, increased frequency of sex, unprotected sex, and recent partner changes have also been reported to increase the risk of BV (Schwebke et al., 1999, Nilsson et al., 1997). It is also prevalent in women with a prior or current STD however the occurrence of BV may be the direct consequence of exposure to the infectious pathogen not the sexual behavior.

IUD use: Women who use an intrauterine device (IUD) for birth control have a higher risk of bacterial vaginosis.

Douching: The practice of rinsing out the vagina with water or a cleansing agent (douching) upsets the natural balance of the


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