Vaginal microbial communities can be dominated by anaerobic (community state type IV, CST IV) or Lactobacillus (other CSTs) species. CST IV is a risk factor for spontaneous preterm birth (sPTB) and is more common among Black than White populations. In the US, average air pollution exposures are higher among Black compared to White people and exert systemic health effects. We sought to (1) quantify associations of air pollution, specifically particulate matter <2.5 µm in diameter (PM2.5) with vaginal microbiota and (2) explore the extent to which racial differences in PM2.5 exposure might explain racial disparities in CST IV.

Higher PM2.5 exposure was associated with CST IV (aOR 1.41, 95% CI 1.04-1.92). Further adjustment for race/ethnicity attenuated the association (aOR 1.35, 95% CI: 0.99-1.86). Black participants (vs. White) had higher median PM2.5 exposure (10.6 vs. 9.6 μg/m3, P< 0.001) and higher prevalence of CST IV (46% vs. 11%, P< 0.001). Mediation analysis revealed that higher PM2.5 exposure may explain 5.4% (P=0.028) and 4.9% (P=0.066) of the Black-White disparity in CST IV in unadjusted and adjusted models, respectively. PM2.5 exposure may partially explain racial differences in vaginal microbiota, reflecting responses to environmental stimuli as opposed to innate, genetic, biological differences. Further research is warranted to discover how environmental exposures affect microbial composition and perpetuate racial health disparities.