title: Rapid, highly discriminatory binary genotyping to demonstrate methicillin-resistant Staphylococcus aureus transmission in a tertiary care intensive care unit.
abstract: OBJECTIVE
  No previous studies of methicillin-resistant Staphylococcus aureus (MRSA) epidemiology in adult intensive care units (ICUs) have assessed the utility of rapid, highly discriminatory strain typing in the investigation of transmission events.
  
  
  METHODS
  Observational.
  
  
  METHODS
  A 22-bed medical-surgical adult ICU. Patients Those admissions MRSA-positive on initial screening and all admissions <48 hours in duration were excluded, leaving a cohort of 653 patients (median age, 61 years; APACHE-II, 19).
  
  
  METHODS
  We conducted this study of MRSA transmission over 1 year (August 1, 2011 to July 31, 2012) using a multiplex PCR-based reverse line blot (mPCR/RLB) assay to genotype isolates from surveillance swabs obtained at admission and twice weekly during ICU stays. MRSA prevalence and incidence rates were calculated and transmission events were identified using strain matching. Colonization pressure was calculated daily by summation of all MRSA cases.
  
  
  RESULTS
  Of 1,030 admissions to ICU during the study period, 349 patients were excluded. MRSA acquisition occurred during 31 of 681 (4.6%) remaining admissions; 19 of 31(61%) acquisitions were genotype-confirmed, including 7 (37%) due to the most commonly transmitted strain. Moving averages of MRSA patient numbers on the days prior to a documented event were used in a Poisson regression model. A significant association was found between transmission and colonization pressure when the average absolute colonization pressure on the previous day was ≥3 (χ2=7.41, P=0.01).
  
  
  CONCLUSIONS
  mPCR/RLB characterizes MRSA isolates within a clinically useful time frame for identification of single-source clusters within the ICU. High MRSA colonization pressure (≥3 MRSA-positive patients) on a given day is associated with an increased likelihood of a transmission event.
authors: 1Junior Medical Officer,Royal Adelaide Hospital,Adelaide,Australia.
authors: C W
authors: CW
authors: Sadler
authors: 2Intensive Care Unit,Westmead Hospital,Sydney,Australia.
authors: V
authors: V
authors: Nayyar
authors: 2Intensive Care Unit,Westmead Hospital,Sydney,Australia.
authors: E R
authors: ER
authors: Stachowski
authors: 3Centre for Infectious Diseases and Microbiology,Westmead Hospital,Sydney,Australia.
authors: M V N
authors: MV
authors: O'Sullivan
authors: 3Centre for Infectious Diseases and Microbiology,Westmead Hospital,Sydney,Australia.
authors: G L
authors: GL
authors: Gilbert
authors: 4University of Sydney,Australia.
authors: K
authors: K
authors: Byth
mesh_terms: D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D060005:Genotyping Techniques; D006801:Humans; D015994:Incidence; D007362:Intensive Care Units; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics* / Q000302:isolation & purification; D008875:Middle Aged; D060885:Multiplex Polymerase Chain Reaction; D015995:Prevalence; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission*; D062606:Tertiary Care Centers