Pathogen-Specific Clustering of Nosocomial Blood Stream Infections in Very Preterm Infants

BACKGROUND AND OBJECTIVES: Nosocomial infections in NICUs tend to cluster, sometimes as devastating outbreaks, but pathogen-specific transmission probabilities are unknown. We aimed to quantify the pathogen-specific risk of a blood stream infection (BSI) in preterm infants after an index case with that pathogen in the same department. METHODS: Data of 44 818 infants below 1500 g birth weight of the German NICU surveillance system (2000–2011) were used to calculate the probability of a BSI in the presence or absence of another infant in the same unit with a same-pathogen BSI. RESULTS: The relative risk was similar for the more common pathogens, Enterococcus spp (4.3; 95% confidence interval: 2.7–6.9; n = 243), Enterobacter spp (7.9, 5.4–11.4; n = 246), Escherichia coli (7.9; 5.1–12.1; n = 210), Candida albicans (8.7; 5.0–15.4; n = 138), Staphylococcus aureus (9.5; 7.6–12.1; n = 407) and Klebsiella spp (13.1; 9.0–19.1; n = 190) but markedly elevated for Serratia spp (77.5; 41.1–146.1; n = 58) and Pseudomonas aeruginosa (64.5; 25.7–162.1; n = 38). Rates of BSI per 100 exposed infants ranged between 2.21 ( Enterococcus ) and 8.15 ( Serratia ). The same pattern emerged after adjustments were made for patients’ characteristics or when the analysis was restricted to positive blood cultures during the preceding 30 days. CONCLUSIONS: Although BSIs with P aeruginosa or Serratia spp in preterm infants are rare, they are associated with a markedly elevated risk of secondary same-pathogen BSI and should prompt intensified active surveillance and infection control measures.