Statistical analysis of clinical characteristics was performed as described previously.22 Before analysis, normal distribution and homogeneity of the variances were tested. Values were represented as means and standard deviations. The groups were specified a priori. For selected parameters, data were shown and analyzed as lowest and highest quartiles. Paired 2-tailed Student t test was used to compare baseline to exit characteristics, and significance level was set at P < 0.05. For each sample and taxon, relative abundance was calculated by dividing the absolute number of sequences by the rarefied number of sequences for each sample (6280 sequences). At the exit, differences in microbiota taxonomic abundance were tested using Kruskal–Wallis nonparametric test. False discovery rate–corrected P values were estimated as described by Benjamini and Hochberg 31 for all taxa comparisons. The significance was set at P < 0.05 for Kruskal–Wallis test. For false discovery rate, significance was determined at P < 0.05 (5% false positive allowed), and tendency for significance was at P < 0.1 (10% false positive allowed). The unpaired student's t test was used to compare Shannon's diversity index (P < 0.05). All statistical analyses were performed using SAS 9.2 statistical software.