title: Impact of combined low-level mupirocin and genotypic chlorhexidine resistance on persistent methicillin-resistant Staphylococcus aureus carriage after decolonization therapy: a case-control study.
abstract: BACKGROUND
  The clinical importance of low-level mupirocin resistance and genotypic chlorhexidine resistance remains unclear. We aimed to determine whether resistance to these agents increases the risk of persistent methicillin-resistant Staphylococcus aureus (MRSA) carriage after their use for topical decolonization therapy.
  
  
  METHODS
  A nested case-control study was conducted of MRSA carriers who received decolonization therapy from 2001 through 2008. Cases, patients who remained colonized, were matched by year to controls, those in whom MRSA was eradicated (follow-up, 2 years). Baseline MRSA isolates were tested for mupirocin resistance by Etest and chlorhexidine resistance by qacA/B polymerase chain reaction. MRSA carriers with high-level mupirocin resistance were excluded. The effect of the primary exposure of interest, low-level mupirocin and genotypic chlorhexidine resistance, was evaluated with multivariate conditional logistic regression analysis.
  
  
  RESULTS
  The 75 case patients and 75 control patients were similar except that those persistently colonized were older (P = .007) with longer lengths of hospital stay (P = .001). After multivariate analysis, carriage of combined low-level mupirocin and genotypic chlorhexidine resistance before decolonization independently predicted persistent MRSA carriage (odds ratio [OR], 3.4 [95% confidence interval {CI}, 1.5-7.8]). Other risk factors were older age (OR, 1.04 [95% CI, 1.02-1.1]), previous hospitalization (OR, 2.4 [95% CI, 1.1-5.7]), presence of a skin wound (OR, 5.7 [95% CI, 1.8-17.6]), recent antibiotic use (OR, 3.1 [95% CI, 1.3-7.2]), and central venous catheterization (OR, 5.7 [95% CI, 1.4-23.9]).
  
  
  CONCLUSIONS
  Combined low-level mupirocin and genotypic chlorhexidine resistance significantly increases the risk of persistent MRSA carriage after decolonization therapy. Institutions with widespread use of these agents should monitor for resistance and loss of clinical effectiveness.
authors.affiliation: Infection Control Program, Department of Infectious Diseases and Microbiology, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Andie S
authors.initials: AS
authors.lastname: Lee
authors.forename: Marina
authors.initials: M
authors.lastname: Macedo-Vinas
authors.forename: Patrice
authors.initials: P
authors.lastname: François
authors.forename: Gesuele
authors.initials: G
authors.lastname: Renzi
authors.forename: Jacques
authors.initials: J
authors.lastname: Schrenzel
authors.forename: Nathalie
authors.initials: N
authors.lastname: Vernaz
authors.forename: Didier
authors.initials: D
authors.lastname: Pittet
authors.forename: Stephan
authors.initials: S
authors.lastname: Harbarth
mesh_terms: D000287:Administration, Topical; D000368:Aged; D000369:Aged, 80 and over; D000891:Anti-Infective Agents, Local / Q000008:administration & dosage / Q000494:pharmacology*; D002353:Carrier State / Q000188:drug therapy* / Q000382:microbiology; D016022:Case-Control Studies; D002710:Chlorhexidine / Q000008:administration & dosage / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005260:Female; D005798:Genes, Bacterial; D005838:Genotype; D006801:Humans; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000302:isolation & purification*; D008875:Middle Aged; D016712:Mupirocin / Q000008:administration & dosage / Q000494:pharmacology*; D016133:Polymerase Chain Reaction / Q000379:methods; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D016896:Treatment Outcome
chemical_list: D000891:Anti-Infective Agents, Local; D004269:DNA, Bacterial; D016712:Mupirocin; D002710:Chlorhexidine