Background: In the spring of 2013,a novel avian-origin influenza A (H7N9) virus emerged and spread among humans in Eastern China.Treatment with antiviral drugs was initiated in patients at a median of 7 days after the onset of illness.Prophylactic treatment with antibiotics and probiotics for secondary infection is as important as antiviral treatment.This study aims to assess the ability of probiotic treatment to reduce the risk of secondaryinfections resulting from infection with the H7N9 virus.Methods: Between April 1 and May 10,2003,113 stool,sputum,and blood specimens were collected and analyzed by denaturing gradient gel electrophoresis (DGGE) to determine the composition of the patient microbiomes.Levels of C-reactive protein (CRP) in the blood of each patient were also monitored in real time to identify any potential inflammatory response.Cluster analysis of DGGE pattem profiles was employed to create a phylogenetic tree for each patient,and multidimensional scaling (MDS) and principal component analysis (PCA) were performed to visualize relationships between individual lanes.Microbial diversity was calculated using Gel-Pro analyzer and Past software.Results: Five patients had secondary bacterial infections,including Klebsiella pneumonia,Acinetobacter baumanii and Candida albicans infection.A trend toward decreased CRP levels in H7N9 patients was observed,indicating a lack of a proinflammatory response.Shannons diversity index and species richness were moderately lower in all treated patient groups compared to the control group.The DGGE profiles of fecal samples obtained at different time points from the same individual were clearly different,particularly for patients with secondary infections.Conclusion: H7N9 infection can cause perturbation of the intestinal microbiota in humans,leading to secondary infection.C.butyricum administration may promote partial recovery of the microbiota composition after antibiotic cessation,and B.subtilis and E.faecium may also play a role in preventing secondary infections in these patients.