Utility of Amsel criteria, Nugent score, and quantitative PCR for Gardnerella vaginalis, Mycoplasma hominis, and Lactobacillus spp. for diagnosis of bacterial vaginosis in human immunodeficiency virus-infected women

Abstract

Bacterial vaginosis (BV) is a clinical syndrome presenting with a malodorous vaginal discharge and increased vaginal pH. Diagnosis has been based on clinical Amsel criteria and direct Gram stain of vaginal secretions. Human immunodeficiency virus (HIV)-infected participants in the Women's Interagency HIV Study contributed cervicovaginal lavage (CVL) samples. Lactobacilli, Gardnerella vaginalis, and Mycoplasma hominis in cervicovaginal lavage samples were quantified by PCR. Gynecologic evaluation included Nugent score and Amsel criterion assessment. We compared the gold standard Nugent score to Amsel criteria and quantitative bacterial PCR for diagnosing BV in 203 CVL samples from women with Nugent scores of 7 to 10 (BV group) and 203 samples from women with BV Nugent scores of 0 to 3 ("No-BV" group). Only 75 of the 203 CVL samples from women with Nugent scores of 7 to 10 met positive Amsel criteria. Increasing levels of G. vaginalis and M. hominis and decreasing levels of lactobacilli were significantly associated with BV by Nugent score. Of the group with Nugent scores of 7 to 10, 83% and 81% had log(10) G. vaginalis counts and log(10) M. hominis counts greater than 6.81 and 4.82, respectively, while only 30% and 31% of the group with Nugent scores of 0 to 3 were above these thresholds, respectively. There was significant overlap in the log(10) lactobacillus counts between the two groups. Utilizing all three log(10) bacterial counts (G. vaginalis, M. hominis, and lactobacilli) in our model improved the sensitivity and specificity to 83% and 78%, respectively, in comparison with Nugent score. In this cohort, Amsel criteria were poorly predictive of BV. PCR quantification of G. vaginalis and M. hominis from CVL is significantly more sensitive than Amsel criteria for diagnosing BV.

FIG. 1.

Box plot diagram showing the distribution of log₁₀ bacterial counts for each bacterial species, Gardnerella vaginalis (G vag), Mycoplasma hominis (M hom), and Lactobacillus spp. (Lacto) by Nugent score. The cut points identified for G. vaginalis, M. hominis, and Lactobacillus spp. that differentiate the BV group from the No-BV group are denoted by a dashed line.

FIG. 2.

ROC curves for combinations of one or more bacterial counts as diagnostic criteria for BV. MH, M. hominis; GV, G. vaginalis; LA, lactobacilli; AUC, area under the curve. The closer the AUC is to 1.0, the better the bacterial counts predict BV. The bottom row of curves shows that the inclusion of all three quantitative bacterial counts in the model provides better predictive power. The addition of Amsel criteria further improves the power, and inclusion of plasma viral load does not change the power.