A case control study evaluated the patterns of the intestinal microbiome prior to the development of NEC in 12 infants and compared these with the patterns in 26 control infants without NEC. Fecal samples were collected from all these infants periodically from birth until 60 postnatal days or until discharge. All infants were less than 32 weeks gestation. A longitudinal analysis of the 16S rRNA genes was conducted on 312 samples. The researchers found that the microbiome undergoes dynamic development during the first two months of life. The pattern of progression with microbiota colonization was different between cases and controls. A clear separation was noted in the colonization patterns between early-onset (22 days or less) NEC cases and their controls. This separation was less clear for late-onset NEC versus controls. The specific infectious agent associated with NEC may vary by the age of the infant at disease onset. Another finding in this study was that intravenous antibiotics may have an impact on microbial diversity.