Probiotics are beneficial bacteria that modify the intestinal flora. Breastfed infants have a decreased rate of infectious diarrhea compared with formula-fed infants, a difference thought to be caused by proliferation of pro-biotic bacteria in the intestines of breastfed infants. In this study, probiotic-enriched formula was used in infants attending child care centers to determine whether this intervention would decrease the rate of respiratory and gastrointestinal infections.

Healthy infants who were exclusively formula-fed and were four to 10 months of age were recruited from 14 child care centers. Infants were randomized to a control group (formula without probiotic supplementation), to a formula supplemented with Bifidobacterium lactis, or to formula with Lactobacillus reuteri. Growth parameters were monitored at baseline and at four, eight, and 12 weeks. Parents of the participants kept track of respiratory and gastrointestinal symptoms, as well as fever, absences from the centers, clinic visits, and medication prescriptions. Ill children were examined daily by a research team pediatrician. Outcome measures were fever and gastrointestinal or respiratory symptoms. Day care absences, physician visits, and antibiotic medications also were measured.

Of 201 enrollees, 60 infants were in the control group, 73 were in the B. lactis group, and 68 were in the L. reuteri group. No significant differences were noted among the groups in terms of physical parameters, parental smoking, family size, or formula volume. Infants in the control group had significantly more febrile episodes and more frequent and longer-lasting diarrhea than did infants in the probiotic groups. The L. reuteri group had significantly fewer febrile days, clinic visits, child care absences, and antibiotic prescriptions than the other two groups. Respiratory illnesses did not differ among groups, and no adverse effects were noted in any of the groups.

The authors conclude that of the two commonly used probiotics, L. reuteri was particularly effective in reducing gastrointestinal symptoms in infants attending child care. However, differences were less than one day’s duration. Also, little is known about tailoring the various available probiotic species to different indications.