title: Meticillin-resistant Staphylococcus aureus in elderly residents of care homes: colonization rates and molecular epidemiology.
abstract: BACKGROUND
  Meticillin-resistant Staphylococcus aureus (MRSA) is a significant cause of mortality and morbidity in healthcare and community settings; however, there is a paucity of large-scale, longitudinal studies monitoring the occurrence of MRSA in the care home setting.
  
  
  OBJECTIVE
  To determine the molecular epidemiology of MRSA colonizing elderly residents of care homes.
  
  
  METHODS
  Residents in 65 care homes in Leeds, UK, were screened for MRSA nasal colonization in four consecutive years (2006-2009). Isolates were characterized using antibiotic susceptibility testing, detection of the Panton-Valentine leucocidin (PVL) locus, accessory gene regulator allotyping, characterization of the staphylococcal cassette chromosome mec element, spa-typing and pulsed-field gel electrophoresis.
  
  
  RESULTS
  MRSA was recovered from 888 nasal swabs of 2492 residents and prevalence was similar (19-22%) throughout the study. Resistance to ≥3 antibiotic classes was common (34%), but resistance to only β-lactam agents was rare (3%); no PVL-positive isolates were identified. Most isolates were related to healthcare-associated epidemic-MRSA type 15 (EMRSA-15, ST22-IV); such isolates decreased in prevalence during the study (86-72%; P < 0.0001, χ(2)-test). The remainder belonged to five different multi-locus sequence type clonal complexes (CC). Most notably, CC59 strains increased in prevalence (10-25%; P < 0.0001, χ(2)-test) and were associated with high-level mupirocin resistance.
  
  
  CONCLUSIONS
  The molecular epidemiology of MRSA in care homes is complex and dynamic. There was a high, consistent prevalence of MRSA nasal colonization, dominated by healthcare-associated strains. Vigilance is recommended; however, as high-level mupirocin resistance was associated with a single clonal group (CC59) that significantly increased in prevalence during the study.
authors: Leeds Teaching Hospitals NHS Trust, Department of Microbiology, Old Medical School, Leeds, UK. carolyne.horner@leedsth.nhs.uk
authors: C
authors: C
authors: Horner
authors: P
authors: P
authors: Parnell
authors: D
authors: D
authors: Hall
authors: A
authors: A
authors: Kearns
authors: J
authors: J
authors: Heritage
authors: M
authors: M
authors: Wilcox
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D005838:Genotype; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D058889:Molecular Typing; D009735:Nursing Homes; D015995:Prevalence; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D006113:United Kingdom / Q000453:epidemiology; D037521:Virulence Factors / Q000235:genetics
chemical_list: D037521:Virulence Factors