Nosocomial colonization due to imipenem-resistant Pseudomonas aeruginosa epidemiologically linked to breast milk feeding in a neonatal intensive care unit.

Aim: We describe a one-year investigation of colonization by imipenemresistant,metallo-β-lactamase (MBL) producing Pseudomonas aeruginosa ina neonatal intensive care unit (NICU) of the University Hospital of Palermo,Italy. Methods: A prospective epidemiological investigation was conductedin the period 2003 January to 2004 January. Rectal swabs were collectedtwice a week from all neonates throughout their NICU stay. MBL productionby imipenem-resistant strains of P aeruginosa was detected by phenotypicand molecular methods. Pulsed field gel electrophoresis (PFGE) was carriedout on all isolates of P aeruginosa. The association between risk factors andcolonization by imipenem-resistant, imipenem-susceptible P aeruginosa isolatesand other multidrug-resistant Gram negative (MDRGN) organisms was analyzedfor variables present at admission and during the NICU stay. Data analysis wascarried out by the Cox proportional hazards regression model. Results: Twentytwoof 210 neonates were colonized with imipenem-resistant, MBL-producingP aeruginosa isolates and 14 by imipenem-susceptible P aeruginosa isolates.A single pulsotype, named A, was shared by all imipenem-resistant isolates.Colonization by P aeruginosa of pulsotype A was positively correlated withbreast milk feeding and administration of ampicillin-sulbactam, and inverselycorrelated with exclusive feeding by formula. In the Cox proportional hazardsregression model, birthweight of more than 2500 g and breast milk feedingwere independently associated with an increased risk of colonization by MBLproducingP aeruginosa. Conclusion: The results strongly support an associationbetween colonization by a well-defined imipenem-resistant, MBL producing Paeruginosa strain and breast milk feeding. Such a study may highlight the needfor implementation of strategies to prevent expressed breast milk from becominga vehicle of health care-associated infections.