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

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.

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.

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.

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.