Transmission of colistin-resistant Pseudomonas aeruginosa between patients attending a pediatric cystic fibrosis center

We report on an outbreak of colistin-resistant Pseudomonas aeruginosa (CRPA) that occurred in a United Kingdom pediatric cystic fibrosis (CF) unit and involved six children over a period of 5 years. All CRPA-positive children had received aerosolized colistin therapy before first isolation of resistant organisms (mean duration, 3.1 years). Four of the 6 had also received courses of intravenous colistin in the year before the first isolation of CRPA. No impact of CRPA acquisition on respiratory function, clinical condition, or radiological parameters could be demonstrated. Four of the 6 children carried isolates of CRPA indistinguishable on genotyping. Two of these 4 children were sisters. The other 2 were on the same ward together at time of first isolation, and subsequently shared overlapping admissions with one of the sisters. While there is no conclusive evidence for the route of transmission, the frequency of overlapping in-patient admissions between 3 of these patients is suggestive of patient-to-patient transfer in the nosocomial setting. CF clinicians should be aware that colistin resistance can occur in P. aeruginosa, and some of these strains are capable of spread within CF units.