Nosocomial diarrhea is any diarrhea that a patient contracts in a health-care institution. In children, it is commonly caused by enteric pathogens, especially rotavirus. The reported incidence ranges from 4.5 to 22.6 episodes per 100 admissions. Nosocomial diarrhea may prolong the hospital stay and increase medical costs. One of the potential strategies for the prevention of nosocomial infections is the use of probiotics. The number of studies have shown the efficacy of Lactobacillus reuteri (DSM 17938) in the treatment of acute diarrhea. However, there are no data on the efficacy of L. reuteri in the prevention of nosocomial diarrhea. The investigators, therefore, plan to perform the study with the aim of evaluating the role of Lactobacillus reuteri DSM 17938 administration in the prevention of nosocomial gastroenteritis in a pediatric hospital setting.