Consumption of Chlorhexidine and Mupirocin Across the Health System of the US Department of Defense (DOD) and the Incidence of the qacA/B and mupA Genes in the DOD Facilities of the National Capital Region

To the Editor – Despite heightened concern for increased resistance to mupirocin and chlorhexidine [1–4], reports that assess the relationship between consumption of the agents and genotypic resistance are scarce. We sought to determine if there were any significant trends in mupirocin and chlorhexidine consumption in the nationwide healthcare system of the US Department of Defense (DOD) and in a subset of DOD hospitals in the National Capital Region (DODNCR) that also conduct active surveillance for mupA and qacA/B. All consecutive methicillin-resistant Staphylococcus aureus (MRSA) isolated from clinical cultures in the DODNCR from 1 June 2014 to 31 December 2015 were prospectively included. Deduplication was based on 1 isolate per patient (the first). Isolates were tested for mupA and qacA/B and 4 virulence-related genes using a multiplex polymerase chain reaction (PCR) assay, as previously described [5, 6]. Milliliters of chlorhexidine and mupirocin were tabulated for the DOD-NCR and the entire DOD as previously described [7]. Chlorhexidine consumption included liquid soaps and prescriptions for medicated wash cloths but not for oral rinse. Trend analysis was performed using generalized linear regression on SAS, version 12, adjusting for any seasonal variation in the data. A total of 458 unique MRSA isolates (monthly average = 47) were obtained from the DOD-NCR. Of these, 95.0% (435) were from infections (sterile sites or active wounds), with the remainder being colonizing (surface swabs of nares or intact skin). Twenty-five (5.5%) were positive for mupA. The monthly fraction of mupA-positive isolates ranged from 0% to 25%, with a mean of 7.2%. We found only 3 positive qacA/B isolates (0.6%). The monthly fraction of qacA/B-positive isolates ranged from 0% to 11.1%, with a mean of 0.9%. The frequency of mupA or qacA/B positivity did not significantly increase over the observation period. Twenty-three isolates carried the sep gene (5.0%) and 305 (67%) carried the pvl gene. Cfr and etA genes were not detected. Consumption trends varied by patient location (inpatient or ambulatory), stratification (nationwide or region), and hospital type (community hospital or tertiary care referral hospital; Table 1). To our knowledge, we are the first to assess the relationships between genotypic resistance and consumptions of mupirocin and chlorhexidine, both locally–regionally and across a nationwide managed healthcare system. That such resistance did not increase despite increased consumption of mupirocin and chlorhexidine should not be taken as reassurance or a reason for relaxed vigilance of escalating resistance for several reasons. First, like most hospitals, the facilities in this study use PCR for most surveillance to detect colonization. Therefore, very few C O R R E S P O N D E N C E