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508 The Changing Epidemiology of Methicillin-resistant Staphylococcus aureus (MRSA) over 3 years in an Acute Hospital

Saturday, March 20, 2010
Grand Hall (Hyatt Regency Atlanta)
Eilish Creamer, MSc , Royal College of Surgeons in Ireland, Dublin, Ireland
Anthony Dolan, BSc , Royal College of Surgeons in Ireland, Dublin, Ireland
Orla Sherlock, PhD , Royal College of Surgeons in Ireland, Dublin, Ireland
Deirdre Fitzgerald-Hughes, PhD , Royal College of Surgeons in Ireland, Dublin, Ireland
Anna Shore, PhD , School of Dental Science and Dublin Dental Hospital, TCD, Dublin, Ireland
Derek Sullivan, PhD , School of Dental Science and Dublin Dental Hospital, TCD, Dublin, Ireland
Peter Kinnevey , School of Dental Science and Dublin Dental Hospital, TCD, Dublin, Ireland
Angela S. Rossney, PhD , National MRSA Reference Laboratory, Dublin, Ireland
Piaras O'Lorcain, PhD , Health Protection Surveillance Centre, Dublin, Ireland
Robert Cunney, MD , Health Protection Surveillance Centre, Dublin, Ireland
David Coleman, PhD , School of Dental Science and Dublin Dental Hospital, TCD, Dublin, Ireland
Hilary Humphreys, MB, MRCPath , Royal College of Surgeons in Ireland, Dublin, Ireland
Background: MRSA is a problem in many countries including Ireland. A four-year translational research grant was awarded to study the true prevalence of MRSA in patients on four study wards and to evaluate initiatives to reduce MRSA. Following a baseline survey in 2007/08, a prevalence survey was conducted in 2009 on the 4 study wards, plus 4 other wards to assess the changing trends in MRSA rates.

Objective: To determine the prevalence of MRSA in 2009 on the 4 study wards and compare with 4 other wards and also to compare with the rates in 2007-2008.
Methods: All consenting patients in a 700-bed acute tertiary hospital, admitted to 8 wards, 2 medical and 2 surgical study wards, and 2 medical and 2 surgical other wards were screened within 72 hours of admission (‘admission’ patients). In-patients hospitalised for longer than 72 hours were also screened to establish the extent of the MRSA reservoir (‘reservoir’ patients). Specimens were cultured using salt broth enrichment with subsequent subculture onto MRSA-selective chromogenic agar (MRSA-Select, Bio-rad). Environmetal sampling was undertaken to investigate the MRSA burden in the environment. Molecular typing of isolates was undertaken with PFGE, spa and dru typing.
Results: MRSA was isolated from 9/136 (7%) of patients; 1/21 (5%) of ‘admission’ patients and 7% (8/115) of ‘reservoir’ patients.  Comparison of the 4 study and 4 other wards, showed little difference, 5/73 (7%) vs.  4/63 (6%), respectively. Comparison of similar study periods, Week 1 in 2007/08 with 2009, showed a decrease in ‘admission’ patients, 9/45 (20%) vs. 1/21 (5%), and in ‘reservoir’ patients, 24/112 (21%) vs. 8/115 (7%), (p=0.006). Molecular typing of 90 MRSA isolates from 2007/08, revealed that 3/31 (10%) clones accounted for 42/90 (47%), patient isolates. Seven per cent (79/1021) of environmental screenings were MRSA-positive in 2007/08 vs. 21/555 (4%) in 2009. In 2007/08, mattresses, 26/231 (16%) and air samples (patient locker settle plates), 13/126 (10%) were more frequently contaminated by MRSA than in 2009, 11/99 (11%) and 4/99 (4%), respectively.

Conclusions: MRSA screening in 2009 revealed that MRSA rates had decreased since 2007/08, in both ‘admission’ and ‘reservoir’ patients and also in the environment. Three clones accounted for half the patient isolates. The factors responsible for the decrease in MRSA are being investigated as well as the necessity for universal MRSA screening.