The purpose of this study was to determine whether the association between bacterial vaginosis (BV) and incident sexually transmitted infection (STI) varies with more extreme BV scores.
We analyzed the data from 535 women who were enrolled in a randomized trial to promote dual method contraceptive use. Incident STI was defined as any case of Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis , or pelvic inflammatory disease. BV was defined by Gram stain (Nugent score). STI risk was estimated with the use of proportional hazards regression.
Binary (0-6 vs 7-10) and 3-level (negative 0-3, intermediate 4-6, or BV 7-10) categorizations were not associated with time to STI; however, women with the highest Nugent scores (9-10) had a 2.1-fold increased risk of STI (95% confidence interval, 1.05–4.28), compared with women with normal flora.
Nugent score >8 is associated with incident STI. More accurate classification of BV will allow clinicians to identify those women who are at greatest risk of STI.
Bacterial vaginosis (BV) is a common form of vaginitis that is characterized by a shift in vaginal bacterial flora and elevated pH, which is common among reproductive-aged women. Estimates from the National Health and Nutrition Examination Survey indicate that 29% of US women between the ages of 14 and 49 years have BV. Rates of BV are even higher among women who are at high risk for sexually transmitted infection (STI). More than one-half of African American women, 37% of those living below the federal poverty level and 39% of women with ≥2 sexual partners in the past month had BV at the time of their National Health and Nutrition Examination Survey assessment.
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BV has been found to be associated with multiple STIs that include chlamydia, gonorrhea, herpes, human immunodeficiency virus (HIV), and trichomoniasis and is implicated in the development of pelvic inflammatory disease (PID). In prospective studies, BV has been shown to increase the odds of HIV acquisition and herpes simplex virus (HSV; type 2). As these studies highlight, there are multiple common approaches for defining the presence of BV. In the medical literature, BV is most often defined with 2 approaches: (1) Amsel’s criteria (>20% clue cells, whiff test, pH, or characteristic discharge) or (2) Gram stain of vaginal smears that are scored by Nugent’s criteria that reflects the presence of 3 categories of bacterial morphotypes. Most studies estimate STI risk with 2 (BV: yes or no) or 3 level categorizations (normal, intermediate, or BV based on Gram stain score) of BV, but few studies take into consideration the extent of abnormal flora and the impact of alternative diagnostic thresholds for the definition of BV. In this prospective study, we seek to determine whether severity of BV (specifically, measures of extreme cases of anaerobic overgrowth [Gram stain score, 9 or 10]) is associated with incident STI. More accurate classification of BV will allow clinicians to better identify those women who are at the greatest risk of STI.
Materials and Methods
The current study was a secondary analysis of data that had been collected by Project Protect, a randomized clinical trial that was funded by the National Institute of Child Health and Human Development. The methods of this study have been described in detail elsewhere. Briefly, Project Protect evaluated the extent to which a computer-based individualized intervention could improve dual contraceptive method use compared with a computer-based enhanced standard care counseling approach.
Enrollment began in October 1999 and continued through October 2003. Women who were eligible for Project Protect included English-speaking women between the ages of 13 and 35 years who were able and willing to give informed consent. Parental permission and minor assent were obtained for all participants who were <18 years old. Women had to be sexually active with a male partner in the past 6 months and desire to avoid pregnancy for 24 months after random assignment. High-risk women were recruited from 2 specific age groups: (1) all sexually active women who were 13-24 years old and (2) high-risk sexually active women who were 25–35 years old. Women who were >24 years old were determined to be at high-risk if their history included any of the following events: unplanned pregnancy, history of an STI, inconsistent use of contraception, or other factors that placed a patient at above-average risk for unplanned pregnancy or STI (eg, >1 sexual partner in the past 6 months or drug or alcohol abuse). To be eligible for participation in this study, women had to have tested negative for all STIs or, if infected, to accept directly observed therapy with a repeat negative test of cure.
At the time of the initial baseline visit, a member of the research team completed a gynecologic and contraceptive history, performed a pelvic examination, and performed tests for BV and STIs. Strand-based testing (Amplified DNA Assay; Becton-Dickinson, Spanks, MD) was completed for Chlamydia trachomatis and Neisseria gonorrhoeae. Patients were examined for signs of PID and genital HSV infection. Acute PID was diagnosed if patients had signs and symptoms that were consistent with the minimal criteria as outlined by the Centers for Disease Control and Prevention (STD Treatment Guidelines, 2003) and for which no other cause could be identified. Serologic testing was performed for syphilis and HIV. This testing was repeated at 12 and 24 months. Participants were also encouraged to contact the study team between visits if they experienced any gynecologic changes or problems.
Women with a positive test result at the time of initial evaluation were treated and had a test of cure before enrolling; therefore, any positive test after baseline was considered an incident STI. The outcome of interest was defined as the time from baseline to the first positive STI result. If a participant did not have an STI during the follow-up period, their observation time was censored at their last study visit. Censoring allows patients who have not experienced an event (STI) to contribute person-time to the survival analysis.
BV evaluation included both a Gram stain and Amsel’s clinical criteria. Amsel’s criteria included 4 clinical symptoms: (1) positive whiff test; (2) presence of thin, homogenous white/gray discharge; (3) pH > 4.5; or (4) >20% clue cells. Nugent’s criteria estimates relative prevalence of bacterial morphotypes (lactobacilli, Gardnerella vaginalis/Bacteroides , and Mobiluncus ). The Nugent score is calculated by an assessment of the presence of large Gram-positive rods ( Lactobacillus morphotypes; scored from 4–0), small Gram-variable rods ( G vaginalis morphotypes; scored from 0–4), and curved Gram-variable rods ( Mobiluncus spp morphotypes; scored from 0–2). Scores ranged from 0–10, with scores from 7–10 typically considered evidence of BV. Nugent scores were completed by the laboratory of Dr Sharon Hillier at the University of Pittsburgh.
We investigated a number of different categorizations of BV. BV was defined first based on Amsel’s clinical criteria (1, total number of criteria; 2, ≥2 criteria vs 0–1; 3, ≥3 criteria vs <3 criteria; 4, all 4 criteria) and then by Gram stain Nugent score (1, continuous [0–10]; 2, dichotomous score <7 vs 7–10; 3 groups, 0–3 [negative], 4–6 [intermediate] vs 7–10 [BV]; 4 categories, score 0–3, 4–6, 7–8 vs 9–10; and 3 groups based on Gram stain, score 0–4, 4–8 vs 9–10).
All participants completed a self-administered questionnaire and a more extensive computer-based survey that collected demographic, reproductive, and sexual history data at the time of random assignment. Patients self-identified their race/ethnicity as Hispanic vs non-Hispanic, African American (black), Caucasian (white), or other. Factors that potentially were associated with incident STIs were evaluated as potential confounders. These included age, education, annual income, current cigarette smoking, pregnancy history (nulligravid or nulliparous), history of STI, history of having exchanged sex for drugs or money, reported the use of condoms every time they had sex at baseline, and lifetime and last month sexual partners.
The data were analyzed with SAS software (version 9.1; SAS Institute Inc, Cary, NC). We described the sample in terms of reproductive health history and demographics and assessed the distribution of the exposure (incident BV) in our study sample. Categorical variables were compared with either a χ 2 or Fisher’s exact test, as appropriate. Survival curves were estimated with the use of the Kaplan-Meier method and compared with the use of the log-rank test. Univariable and multivariable comparisons were conducted by Cox proportional hazards regression. As a secondary analysis, the sample size was limited to the 535 women in Project Protect. For our primary analyses that examined the comparison of Nugent scores of 9 or 10 compared with an expanded intermediate (4-8) and negative (0-3), our power was calculated to be 84% (from estimates obtained in this analysis). This study was approved by the Women and Infants’ Hospital and the University of Rhode Island Institutional Review Boards.
All 535 women who were enrolled in Project Protect were at high risk for STI, which was determined by age or high-risk sexual behavior. Three-quarters of the women were ≤24 years old; one-half of the women were white, and one-quarter of the women were black. One-half of the women had a previous unintended pregnancy or STI, and 1 in 5 women reported consistent condom use at the time of enrollment. Fifty-two percent (95% confidence interval [CI], 48–57) of the women had ≥6 lifetime sexual partners, and 15% (95% CI, 12–18) of the women had ≥2 sexual partners in the past month. BV positivity was associated significantly with increasing age, self-reported black race, previous live birth, previous STI, number of sexual partners in the past month, and sex after drinking or drug use ( Table 1 ). Although not statistically significant, BV positivity was lower among consistent condom users and women with fewer lifetime sexual partners.