title: Whole-genome sequencing shows that patient-to-patient transmission rarely accounts for acquisition of Staphylococcus aureus in an intensive care unit.
abstract: BACKGROUND
  Strategies to prevent Staphylococcus aureus infection in hospitals focus on patient-to-patient transmission. We used whole-genome sequencing to investigate the role of colonized patients as the source of new S. aureus acquisitions, and the reliability of identifying patient-to-patient transmission using the conventional approach of spa typing and overlapping patient stay.
  
  
  METHODS
  Over 14 months, all unselected patients admitted to an adult intensive care unit (ICU) were serially screened for S. aureus. All available isolates (n = 275) were spa typed and underwent whole-genome sequencing to investigate their relatedness at high resolution.
  
  
  RESULTS
  Staphylococcus aureus was carried by 185 of 1109 patients sampled within 24 hours of ICU admission (16.7%); 59 (5.3%) patients carried methicillin-resistant S. aureus (MRSA). Forty-four S. aureus (22 MRSA) acquisitions while on ICU were detected. Isolates were available for genetic analysis from 37 acquisitions. Whole-genome sequencing indicated that 7 of these 37 (18.9%) were transmissions from other colonized patients. Conventional methods (spa typing combined with overlapping patient stay) falsely identified 3 patient-to-patient transmissions (all MRSA) and failed to detect 2 acquisitions and 4 transmissions (2 MRSA).
  
  
  CONCLUSIONS
  Only a minority of S. aureus acquisitions can be explained by patient-to-patient transmission. Whole-genome sequencing provides the resolution to disprove transmission events indicated by conventional methods and also to reveal otherwise unsuspected transmission events. Whole-genome sequencing should replace conventional methods for detection of nosocomial S. aureus transmission.
authors: Department of Microbiology and Infection, Royal Sussex County Hospital, Brighton.
authors: James R
authors: JR
authors: Price
authors: Tanya
authors: T
authors: Golubchik
authors: Kevin
authors: K
authors: Cole
authors: Daniel J
authors: DJ
authors: Wilson
authors: Derrick W
authors: DW
authors: Crook
authors: Guy E
authors: GE
authors: Thwaites
authors: Rory
authors: R
authors: Bowden
authors: A Sarah
authors: AS
authors: Walker
authors: Timothy E A
authors: TE
authors: Peto
authors: John
authors: J
authors: Paul
authors: Martin J
authors: MJ
authors: Llewelyn
mesh_terms: D000328:Adult; D000368:Aged; D003428:Cross Infection / Q000382:microbiology / Q000635:transmission*; D005260:Female; D016680:Genome, Bacterial; D015894:Genome, Human; D006801:Humans; D008297:Male; D008875:Middle Aged; D017720:Molecular Epidemiology; D058889:Molecular Typing; D017422:Sequence Analysis, DNA; D013203:Staphylococcal Infections / Q000382:microbiology / Q000635:transmission*; D013211:Staphylococcus aureus / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification
keywords: Staphylococcus aureus transmission; adult; intensive care unit; spa typing; whole-genome sequencing