Impact of exposure to air pollution on cervicovaginal microbial communities

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 (PM_2.5), with CST IV and (2) explore the extent to which racial disparities in PM_2.5 exposure might explain racial differences in the prevalence of CST IV.

Methods: We performed a secondary analysis of 566 participants of the Motherhood & Microbiome study. PM_2.5 exposures were derived from a machine learning model integrating NASA satellite and EPA ground monitor data. Previously, cervicovaginal swabs from 15 to 20 weeks' gestation were analyzed using 16 S rRNA sequencing and hierarchical clustering assigned CSTs. Multivariable logistic regression models calculated adjusted odds ratios of CST IV (vs. other CSTs) per interquartile range (IQR) increment of PM_2.5. Race-stratified and mediation analyses were performed.

Higher PM_2.5 exposure was associated with CST IV (aOR 1.39, 95% CI 1.02-1.91). Further adjustment for race/ethnicity attenuated the association (aOR 1.34, 95% CI: 0.97-1.83). Black participants (vs. White) had higher median PM_2.5 exposure (10.6 vs. 9.6 μg/m³, P < 0.001) and higher prevalence of CST IV (47% vs. 11%, P < 0.001). Mediation analysis revealed that higher PM_2.5 exposure may explain 3.9% (P = 0.038) and 3.3% (P = 0.15) of the Black-White disparity in CST IV in unadjusted and adjusted models, respectively.

PM_2.5 was associated with CST IV, a risk factor for sPTB. Additionally, PM_2.5 exposure may partially explain racial differences in the prevalence of CST IV. Further research is warranted to discover how environmental exposures affect microbial composition and perpetuate racial health disparities.