Are probiotics safe?

The answer seems to be "yes," even for immuno-compromised populations, such as premature neonates. But rare reports of systemic infections involving lactobacilli and bifidobacteria have caused some to question their safety.

The authors of a scientific review appearing in a recent issue of the British Medical Journal point out that while anecdotal cases of Lactobacillus infection do exist, most have occurred in elderly patients or infants, most have been linked to Lactobacillus rhamnosus GG or Lactobacillus casei, and only one was attributable to a probiotic supplement. In addition, sepsis due to Lactobacillus has not been reported in a single prospective randomized study involving probiotics. And systemic infection with Bifidobacterium is even more rare than that with Lactobacillus.

In addition, they explain that in evaluating the safety of agents, one must weigh the risk of sepsis due to Lactobacillus against that of sepsis due to more pathologic species of bacteria and against diseases that probiotic therapy is meant to prevent, such as necrotizing enterocolitis.

Hammerman C, Bin-Nun A, Kaplan M. Safety of probiotics: comparison of two popular strains. BMJ. 2006;333:1006-1008.