This excellent recent paper from Sarma et al brings focus on what the target level of quinolone use should be in order to have an impact on quinolone resistance in Enterobacteriaceae.  It describes the situation across a region of England (9 hospitals and other facilities) where quite stringent control of cephalosporin use was already in place (from August 2007).  A two phase approach to quinolone use control commenced in 2009 and achieved substantial reduction in use from a baseline of 100-150 DDD /1000 patient-days to around 50 DDD/1000 patient-days and then, after the main intervention (administrative controls), below 20 DDD/ 1000 patient-days.  An interrupted time-series analysis documented a highly significant change in quinolone resistance in both community and hospital-associated urinary ESBL (extend-spectrum betalactamase producing- i.e. ceftriaxone resistant) isolates coincident with second phase of usage reduction.  Quinolone resistance also fell in E. coli bloodstream isolates and other urinary Enterobacteriaceae.   Ctx-m-15 ESBLs continued to circulate and a sample of quinolone susceptible versus resistant isolates indicated that the existing prevalent clone had become susceptible.

Comment –  This paper adds to existing evidence as to the dynamic nature of quinolone usage and resistance. It implies that quinolone resistance brings a fitness cost to the organism and that resistance will recede rapidly once selective pressure is reduced.  Furthermore, it is apparent that to have a sustained ecological impact within a hospital, reductions of usage to below 20 DDD / 1000 patient-days are required – this is quite low and will generally require some sort of restrictive administrative measure.  The recommended class substitution that occurred in this study was from quinolones to tigecycline and piperacillin+tazobactam, again interesting to consider.  The influence of prevalent cephalosporin restriction on the study outcomes is uncertain.

Reference – Sarma et al.  J Hosp Infect. 2015 Sep;91(1):68-73.  Effects of fluoroquinolone restriction (from 2007 to 2012) on resistance in Enterobacteriaceae: interrupted time-series analysis.