ObjectiveTo assess the effects ofBifidobacterium longumsubsp.infantisEVC001 (B infantisEVC001) administration on the incidence of necrotizing enterocolitis (NEC) in preterm infants in a single level IV neonatal intensive care unit (NICU).Study designNonconcurrent retrospective analysis of 2 cohorts of very low birth weight (VLBW) infants not exposed and exposed toB infantisEVC001 probiotic at Oregon Health & Science University from 2014 to 2020. Outcomes included NEC incidence and NEC-associated mortality, including subgroup analysis of extremely low birth weight (ELBW) infants. Log-binomial regression models were used to compare the incidence and risk of NEC-associated outcomes between the unexposed and exposed cohorts.ResultsThe cumulative incidence of NEC diagnoses decreased from 11.0% (n = 301) in the no EVC001 (unexposed) cohort to 2.7% (n = 182) in the EVC001 (exposed) cohort (P< .01). The EVC001 cohort had a 73% risk reduction of NEC compared with the no EVC001 cohort (adjusted risk ratio, 0.27; 95% CI, 0.094–0.614;P< .01) resulting in an adjusted number needed to treat of 13 (95% CI, 10.0–23.5) forB infantisEVC001. NEC-associated mortality decreased from 2.7% in the no EVC001 cohort to 0% in the EVC001 cohort (P= .03). There were similar reductions in NEC incidence and risk for ELBW infants (19.2% vs 5.3% [P< .01]; adjusted risk ratio, 0.28; 95% CI, 0.085–0.698 [P= .02]) and mortality (5.6% vs 0%;P< .05) in the 2 cohorts.ConclusionsIn this observational study of 483 VLBW infants,B infantisEVC001 administration was associated with significant reductions in the risk of NEC and NEC-related mortality.B infantisEVC001 supplementation may be considered safe and effective for reducing morbidity and mortality in the NICU.