428. The Application of Whole Genome Sequencing in Understanding the Role of Patients in the Nosocomial Transmission of Staphylococcus aureus
Session: Poster Abstract Session: Novel Devices and Technologies
Thursday, October 18, 2012
Room: SDCC Poster Hall F-H
Posters
  • James Price (IDSA poster).pdf (773.7 kB)
  • Background: Infection control policies aimed at reducing the burden of Staphylococcus aureus disease focus on identifying and decolonising patients carrying methicillin resistant S.aureus (MRSA). However patients continue to acquire S.aureus particularly in high-dependency settings. Our understanding of S.aureus transmission has been limited by poor resolution of typing methods. We have used whole genome sequencing (WGS) to evaluate the role of patients in S.aureus transmission on an intensive care unit (ICU).

    Methods: Between January 2010 and February 2011 patients admitted to Brighton ICU had admission and weekly, serial swabs for S.aureus. All isolates were spa-typed. Acquisition was defined as isolation of S.aureus following a previous negative swab or change in spa-type. Patient-to-patient transmission was defined as acquisition plus overlapping ICU stay with a patient(s) colonised with the same spa-type. Isolates underwent WGS to further explore their relatedness.

    Results: Of 1123 sampled ICU admissions 161 (14.3%) carried S.aureus at admission (34/161 (21%) MRSA). Acquisition of S.aureus was demonstrated for 39/652 patients who had >1 swab. Of these, only 4 met our definition for patient-to-patient transmission, including 3 in an apparent outbreak of a prevalent, nosocomial MRSA spa-type t032. Isolates from 2 transmission events were genetically distinct by WGS (>40 SNVs), refuting the outbreak and leaving only 2/39 likely true patient-to-patient transmission events. Among 35 acquisitions where epidemiological or spa-type evidence did not indicate direct patient-to-patient transmission, WGS revealed 10 clusters of highly related isolates. However, differences between isolates (15-38 SNVs) suggested that these clusters represented transmission events that pre-dated ICU admission.

    Conclusion: A small minority of apparent S.aureus acquisitions on the ICU are consistent with direct patient-to-patient transmission. WGS has the resolution both to rule-out transmission events suggested by patient contact and spa-typing and to identify otherwise unsuspected transmission events. WGS has the potential to characterise pathways of S.aureus transmission that may be targeted to achieve more effective infection control.

    James Price1, Tanya Golubchik2, Elizabeth Batty, PhD2, Camilla Ip2, Kevin Cole3, Daniel Wilson, DPhil2, Tim Peto, MB BS, DPhil4, Derrick Crook, MB, BCh5, Rory Bowden, PhD2, John Paul3 and Martin Llewelyn1, (1)Brighton and Sussex Medical School, Brighton, United Kingdom, (2)Statistics, University of Oxford, Oxford, United Kingdom, (3)Health Protection Agency, Brighton, United Kingdom, (4)NIHR Oxford Biomedical Research Centre, Oxford, United Kingdom, (5)National Institute for Health Research Oxford Biomedical Research Centre, Oxford, United Kingdom

    Disclosures:

    J. Price, None

    T. Golubchik, None

    E. Batty, None

    C. Ip, None

    K. Cole, None

    D. Wilson, None

    T. Peto, None

    D. Crook, None

    R. Bowden, None

    J. Paul, None

    M. Llewelyn, None

    Findings in the abstracts are embargoed until 12:01 a.m. PST, Oct. 17th with the exception of research findings presented at the IDWeek press conferences.