Increasing burden of urinary tract infections due to intrinsic colistin-resistant bacteria in hospitals in Marseille, France

• We investigated whether use of colistin affected the prevalence of infections due to intrinsic colistin-resistant bacteria (CRB) in the university hospitals of Marseille (France).
• Increasing use of colistin aerosol forms was correlated with the increasing number of infections due to CRB in intensive care units and units of long-term healthcare.
• We also identified an increasing number of CRB in emergency and short-term healthcare units.
• Surveillance is warranted to better understand this intriguing epidemiological change.

The emergence of multidrug-resistant (MDR) Gram-negative bacteria has become a major public health problem, eliciting renewed interest in colistin, an old antibiotic that is now routinely used to treat MDR bacterial infections. Here we investigated whether colistin use has affected the prevalence of infections due to intrinsic colistin-resistant bacteria (CRB) in university hospitals in Marseille (France) over a 5-year period. All data from patients infected by intrinsic CRB were compiled from January 2009 to December 2013. Escherichia coli infections were used for comparison. Colistin consumption data were also collected from pharmacy records from 2008 to 2013. A total of 4847 intrinsic CRB infections, including 3150 Proteus spp., 847 Morganella spp., 704 Serratia spp. and 146 Providencia spp., were collected between 2009 and 2013. During this period, the annual incidence rate of hospital-acquired CRB infections increased from 220 per 1000 patients to 230 per 1000 patients and that of community-acquired CRB infections increased from 100 per 1000 patients to 140 per 1000 patients. In parallel, colistin consumption increased 2.2-fold from 2008 to 2013, mainly because of an increase in the use of colistin aerosol forms (from 50 unitary doses to 2926 unitary doses; P < 10−5) that was significantly correlated with an increase in the number of patients positive for CRB admitted to ICUs and units of long-term care between 2009 and 2013 (r = 0.91; P = 0.03). The global rise in infections due to intrinsic CRB is worrying and surveillance is warranted to better characterise this intriguing epidemiological change.