Carbapenem-resistant Enterobacteriaceae and the correlation between carbapenem and fluoroquinolone usage and resistance in the US military health system

• In the health care system, carbapenem and quinolone use increased.
• Incidences of carbapenem resistant Enterobacteriaceae increased and then decreased.
• Inpatient consumption of fluoroquinolones correlated with carbapenem resistance.
• Incidences of resistance and drug consumption may be too low for correlation.
• This is the largest such use/resistance correlation study in the United States to date.

Whether carbapenem or fluoroquinolone usage is correlated with carbapenem-resistant Enterobacteriaceae (CRE) has not been investigated at the level of an entire US nationwide managed health care system. We analyzed 75 million person-years of surveillance and 1,969,315 cultures from all 266 hospitals in the geographically dispersed US military health system. Incidences of CRE remained under 1 case per 100,000 person-years. Incidences of CRE increased relative to 2005 baseline levels in 3 of 7 subsequent years, then decreased in 2012 (P < 0.05). Incident proportions of carbapenem resistance (CR) differed significantly among years, geographical regions, and bacterial species. Although use and resistance strongly correlated (R > 0.80) for several “drug-bug” combinations, none were significant at the national or facility level. One exception was that inpatient consumption of fluoroquinolones was significantly correlated (P = 0.0007) with CR in Escherichia coli when data from the major referral centers of the Southern and Northern regions were combined.