Case-control analysis of endemic Serratia marcescens bacteremia in a neonatal intensive care unit.

Background: Serratia marcescens is an opportunistic gram-negative rod which typically infects compromised hosts.
Objectives: To identify risk factors, signs, and outcomes associated with non-epidemic S marcescens bacteremia in a neonatal intensive care unit (NICU).
Methods: The records of infants with S marcescens bacteremia while in the Yale-New Haven Hospital NICU from 1980-2004 were reviewed. A matched case-control study was performed by comparing each case of S marcescens to 2 uninfected controls and 2 cases of Escherichia coli bacteremia.
Results: Twenty-five sporadic cases of S marcescens bacteremia were identified. Eleven available isolates were determined to be different strains by pulse field gel electrophoresis. Infants with S marcescens bacteremia had median gestational age and birth weight of 28 weeks and 1235 grams, respectively. Compared to matched, uninfected controls, infants with S marcescens bacteremia were more likely to have had a central vascular catheter (OR = 4.33; 95% CI (1.41 to 13.36)) and surgery (OR = 5.67; 95% CI (1.81 to 17.37)), and had a higher overall mortality (44% vs 2%; OR = 38.50; 95% CI (4.57 to 324.47)). Compared to E coli matched controls, infants with S marcescens bacteremia had later onset of infection (median of 33 days of life vs 10; p<0.001), prolonged intubation (OR = 5.76; 95% CI (1.80 to 18.42)), and a higher rate of CVC (OR = 7.77; 95% CI (2.48 to 24.31)) use at the time of infection. A higher rate of meningitis (24% vs 7%; OR = 3.98; 95% CI (1.09 to 14.50)) was observed with S marcescens bacteremia compared to E coli.
Conclusions: S marcescens bacteremia occurs sporadically in the NICU, primarily in premature infants requiring support apparatus late in their hospital course. Associated meningitis is common and mortality high.