Late-onset sepsis frequently complicates prematurity, contributing to morbidity and mortality. Probiotics may reduce mortality and necrotizing enterocolitis (NEC) in preterm infants, with unclear effect on late-onset sepsis. This study aimed to determine the effect of administering a specific combination of probiotics to very preterm infants on culture-proven late-onset sepsis.


A prospective multicenter, double-blinded, placebo-controlled, randomized trial compared daily administration of a probiotic combination (Bifidobacterium infantis, Streptococcus thermophilus, and Bifidobacterium lactis, containing 1 × 109 total organisms) with placebo (maltodextrin) in infants born before 32 completed weeks’ gestation weighing <1500 g. The primary outcome was at least 1 episode of definite late-onset sepsis.


Between October 2007 and November 2011, 1099 very preterm infants from Australia and New Zealand were randomized. Rates of definite late-onset sepsis (16.2%), NEC of Bell stage 2 or more (4.4%), and mortality (5.1%) were low in controls, with high breast milk feeding rates (96.9%). No significant difference in definite late-onset sepsis or all-cause mortality was found, but this probiotic combination reduced NEC of Bell stage 2 or more (2.0% versus 4.4%; relative risk 0.46, 95% confidence interval 0.23 to 0.93, P = .03; number needed to treat 43, 95% confidence interval 23 to 333).


The probiotics B infantis, S thermophilus, and B lactis significantly reduced NEC of Bell stage 2 or more in very preterm infants, but not definite late-onset sepsis or mortality. Treatment with this combination of probiotics appears to be safe.

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