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 (DOD-NCR) that also conduct active surveillance for mupA and qacA/B.

All consecutive methicillin-resistant Staphylococcus aureus (MRSA) isolated from clinical cultures in the DOD-NCR 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).

Table 1.

Average Monthly Change in Mupirocin and Chlorhexidine Consumption in the Department of Defense (DOD) Healthcare System and the DOD National Capital Region Using Generalized Linear Regression

	Mupirocin		Chlorhexidine
	Average Monthly Change	P Value	AverageMonthly Change	P Value
DOD: All Hospitals in DOD including the DOD-NCRa (n = 280)
Inpatient
g	18.18	<.0001
mL			51.33	.08
Prescription for cloths			2.84	.09
Outpatient
g	894.55	.13
mL			704.07	.04
Tertiary Care Referral Hospitals in DOD-NCR (n = 1)
Inpatient
g	–3.90	<.0001
mL			0.09	.15
Outpatient
g	26.53	.06
mL			25.55	.07
Community Hospitals and Ambulatory Clinics in DOD-NCR (n = 6)
Inpatient
g	–0.01	.88
mL			–0.81	.22
Outpatient
g	16.38	.13
mL			20.90	.03

A negative value indicates that the amount used decreased. Values in bold type are statistically significant.

Abbreviations: DOD, Department of Defense; DOD-NCR, DOD National Capital Region.

aAll tertiary care referral hospitals and community hospitals and/or ambulatory clinics in the DOD combined.

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 cultured surveillance/colonizing isolates are available for analysis. As mupirocin and chlorhexidine are used topically, the prevalence of mupA and qacA/B in the subgroup of colonizing isolates is likely higher. Although the DOD and DOD-NCR treat patients of all ages and races (including neonates and elderly), is widely geographically dispersed, and no close-quarter housing units (barracks) are used in the DOD-NCR, these findings may not be generalizable to other populations. Finally although mupirocin and chlorhexidine resistance did not increase in our study or the REDUCE-MRSA trial [4], there is new concern that exposure to chlorhexidine might be associated with colistin resistance [8].