Background: Gram-negative bacilli (GNB) cause as many as 20% of episodes of late-onset sepsis among very low birth weight (VLBW, birth weight < or =1500 g) infants in the neonatal intensive care unit. As the gastrointestinal (GI) tract can serve as a reservoir for GNB, we hypothesized that VLBW infants with prior GI tract colonization with gentamicin-susceptible GNB who developed bloodstream infections (BSI) would do so with gentamicin-susceptible GNB.

Methods: A prospective cohort study of VLBW infants was performed in 2 level III neonatal intensive care units from September 2004 to October 2007. GI tract surveillance cultures were obtained weekly. Risk factors for GNB BSI and for GI tract colonization with GNB were assessed.

Results: Fifty-one (7.3%) of 698 subjects experienced 59 GNB BSIs of which 34 occurred by 6 weeks of life and 625 (90%) of 698 subjects were colonized with GNB. Overall, 25% of BSI and 16% of GI tract isolates were nonsusceptible to gentamicin and colonization with the same species and same gentamicin susceptibility profile preceded 98% of GNB BSIs. Vaginal delivery, birth weight < or =750 g, GI tract pathology, increased use of central venous catheters, use of vancomycin, mechanical ventilation, and H2 blockers/proton pump inhibitors were associated with GNB BSI. Vaginal delivery, birth weight >1000 g, and treatment with carbapenem agents were associated with GNB colonization.

Conclusions: These data support the use of empiric gentamicin to treat late-onset sepsis in infants colonized with gentamicin-susceptible GNB. Targeted GI tract surveillance cultures of infants with specific risk factors during weeks 2 to 6 of life could be used to guide empiric therapy for late-onset sepsis.