Lower perinatal exposure to Proteobacteria is an independent predictor of early childhood wheezing

We postulated that perinatal risk factors for asthma would be associated with early exposure to bacteria or bacterial products. To evaluate this hypothesis, we assessed circulating-free bacterial DNA (cfbDNA) in umbilical cord blood from mother-child pairs (see Table E1 in this article's Online Repository at www.jacionline.org) from Project Viva, a longitudinal study from birth through childhood.1 To assess cfbDNA, we used 16s rRNA sequencing of the V1-3 region from circulating DNA isolated from umbilical cord blood serum.