Probiotics have been extensively studied over the past several years in the prevention and, to a larger extent, in the treatment of diarrheal diseases, especially in pediatric populations. Diarrhea is a symptom, and not a disease. This review will not address chronic disorders associated with diarrhea, or Clostridium difficile-induced diarrhea. Rather it will focus on published clinical trials performed on acute-onset, likely infectious diarrhea occurring in the settings of day-care centers, in the community, acquired in the hospital, antibiotic-associated diarrhea, and treatment of acute infectious diarrhea. For prevention of diarrhea acquired in day-care centers, 9 randomized and placebo-controlled trials have been published, conducted in different parts of the world. Probiotics tested were Lactobacillus GG, Bifidobacterium lactis (alone or in combination with Streptococcus thermophilus, and Lactobacillus reuteri, Lactobacillus rhamnosus (not GG), and Lactobacillus acidophilus, in various trials either alone or in comparison with each other. The evidence of their efficacy in these settings is only modest for the prevention of diarrhea, although somewhat better for prevention of upper respiratory infections. In the community, new trails conducted in underprivileged areas of India, again with modest efficacy. Previous trials that examined the potential role of probiotics in preventing the spreading of diarrhea in hospitalized children had yielded conflicting results. More recently, a large trial in Poland showed, however, rather good evidence of efficacy for Lactobacillus GG. The prevention of antibiotic-associated diarrhea has been the subject of many investigations, both in children and in adults. Most commonly used probiotics were Lactobacillus GG, Lactobacillus acidophilus, Lactobacillus casei, Bifidobacterium ssp, Streptococcus ssp, and the yeast Saccharomyces boulardii. In general, most of these trials do show clear evidence of efficacy, with the 2 most effective strains being Lactobacillus GG and S. boulardii. Evidence is also emerging on the importance of the dose in reducing the incidence of this type of diarrhea, and the incidence of Clostridium difficile-associated postantibiotic diarrhea. As for treatment, a large body of data is available, especially in children, on the effect of several strains of probiotics in treating sporadic infectious diarrhea. The vast majority of the published trials show a statistically significant benefit and moderate clinical benefit of a few, well-identified probiotic strains-mostly Lactobacillus GG and S. boulardii-in the treatment of acute watery diarrhea, and particularly those due to rotavirus. Such a beneficial effect results, on average, in a reduction of diarrhea duration of approximately 1 day. The effect is strain-dependent and dose-dependent.

This review focuses on the efficacy of probiotics for diarrhea in children in different settings: day-care centers, diarrhea acquired in the hospital, antibiotic-associated diarrhea, and treatment of acute infectious diarrhea. For prevention of diarrhea acquired in day-care centers, 5 randomized and placebo-controlled trials have been published. Probiotics tested were Lactobacillus GG, Bifidobacterium lactis (alone or in combination with Streptococcus thermophilus), and Lactobacillus reuteri. The evidence of their efficacy in these settings is only modest: statistically significant for some strains only and in any case of minimal to mild clinical importance. Few trials have examined the potential role of probiotics in preventing the spread of diarrhea in hospitalized children, an event most commonly due to either rotavirus or Clostridium difficile, and they have yielded conflicting results. Overall, these studies provide only weak evidence on the efficacy of probiotics. On the other hand, a large number of trials on the role of probiotics in preventing the onset of antibiotic-associated diarrhea have been published. Most commonly employed probiotics were Lactobacillus GG, Bifidobacterium spp., Streptococcus spp., and the yeast Saccharomyces boulardii. In general, these trials do show clear evidence of efficacy, with the 2 most effective strains being Lactobacillus GG and S. boulardii. Today, we have a large number of published clinical trials on the role of probiotics in treating sporadic infectious diarrhea in children, and many of them are randomized, blinded, and controlled. They consistently show a statistically significant benefit and moderate clinical benefit of a few, well-identified probiotic strains-mostly Lactobacillus GG and S. boulardii, but also L. reuteri-in the treatment of acute watery diarrhea, primarily rotaviral, in infants and young children of developed countries. Such a beneficial effect seems to result in a reduction of diarrhea duration of little more than 1 day, and to be exerted mostly on diarrhea due to rotavirus. The effect is not only strain-dependent, but also dose-dependent, with doses of at least 10 billion/d being necessary.

The use of probiotics in diarrheal diseases of children is increasing. Probiotics, mostly lactic acid bacteria such as Lactobacilli and Bifidobacteria, but also the yeast Saccharomyces boulardii, have been tried in many double-blinded, randomized, placebo-controlled studies, and several well-conducted meta-analyses are now available. There is some evidence of efficacy in the prevention of community-acquired and nosocomial diarrhea. More solid evidence of efficacy is found in the treatment of sporadic, infectious diarrhea, where several probiotics, and especially Lactobacillus GG, have been found capable of reducing by approximately 1 day the duration of diarrhea, shorten the initial phase of watery stools, and reducing hospital stay in developed countries. The effect is best documented in viral diarrheas. Although there are valid conceptual premises for probiotics to be helpful in inflammatory bowel diseases, only 1 trial has been published in children, showing Lactobacillus GG not to be superior to placebo in maintaining remission of Crohn disease. All considered, more research is needed for a better understanding of the role of probiotics in gastrointestinal diseases of children, addressing issues such as pharmacokinetics, mechanism of action, and role of specific probiotics, alone or in combination, in different disorders.