The natural history of bacterial vaginosis diagnosed by gram stain among women in Rakai, Uganda

Abstract

Background: Large datasets for investigating vaginal flora change at frequent, repeated intervals are limited and graphical methods for exploring such data are inadequate. We report 2-year weekly vaginal flora changes based on Gram stain using lasagna plots.

Methods: Weekly vaginal flora patterns were evaluated among 211 sexually experienced women with ≥18 months of follow-up in Rakai, Uganda. Vaginal flora swabs were self-collected weekly and categorized by Nugent Gram stain criteria (0-3, normal; 4-6, intermediate; 7-10, bacterial vaginosis [BV]). Vaginal flora patterns were analyzed as the percentage of weekly observations with BV (longitudinal prevalence) and illustrated by lasagna plots. Characteristics of women were compared across tertiles of longitudinal prevalence of BV.

Results: Ninety-five percent of women had at least 1 episode of BV over 2 years, with one-third of women spending more than half (52%-100%) of their time with BV. Vaginal pH >4.5 increased with increasing tertiles of longitudinal prevalence of BV (P < 0.001). Weekly fluctuation in vaginal flora states, as measured by a change in flora states from the before current visit, was highest in the middle (41.9%) compared with the lower (30.1%) and upper tertiles (27.8%, P < 0.001). HIV status and reported vaginal symptoms did not differ significantly across BV tertiles.

Conclusions: Women exhibited different patterns of vaginal flora changes over time, which could not be described by baseline behaviors. Lasagna plots aided in describing the natural history of BV within and across women and may be applied to future BV natural history studies.

Figure 1. Subject-specific vaginal flora transition states by weekly visits ordered by the 2-year longitudinal prevalence of BV from lowest to highest

In the graph, light blue boxes correspond to normal flora, red boxes to intermediate flora, black boxes to BV, and off-white boxes to missing visits. Yellow lines divide women based on tertiles of their longitudinal prevalence of BV from lowest to highest.

Figure 2. The 2-year longitudinal prevalence of BV per woman ordered from lowest to highest

In the graph, light blue bars correspond to normal vaginal flora, red bars to intermediate flora, black bars to BV, and off-white bars to missing visits. Yellow lines divide women based on tertiles of their longitudinal prevalence of BV from lowest to highest. [This figure represents a within-row sort of BV states from Figure 1].