1542. Measurement and Variation in MRSA Acquisition Rates in Nursing Homes
Session: Poster Abstract Session: Infections in Non-Acute Healthcare Settings
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
Background: Nursing homes (NHs) represent ideal environments for spread of methicillin-resistant Staphylococcus aureus (MRSA).  However, the frequency of MRSA acquisition within NHs remains poorly understood.

Methods: 439 residents in 6 Wisconsin NHs were serially screened for MRSA for up to year. Recovered MRSA isolates were sub-typed using pulsed-field gel electrophoresis. MRSA acquisition incidence density rates (IDRs) were calculated using three different event definitions based on a resident’s prior MRSA status (Event 1:  resident converting from MRSA[-] to MRSA[+]) and the genetic diversity of the recovered strain (a >4-band [Event 2] or ≥6-band [Event 3] difference between the resident's current and previously recovered MRSA strain). Correlation between a facility’s baseline prevalence of MRSA and acquisition IDR was calculated using the Spearman rank correlation coefficient.

Results: 149 of 439 (34%) subjects were identified as MRSA(+) during the study. The absolute number of MRSA acquisitions in study facilities varied substantially based on the event definition employed (range, 52 – 77 acquisition events); the aquisition IDR was 0.88 (Event 1 criteria), 0.84 (Event 2 criteria), and 0.67 (Event 3 criteria) events per 1,000 resident-days, respectively. Risk of MRSA acquisition varied substantially across the 6 NHs (range, 0.57 to 1.35 acquisition events per 1,000 resident-days), regardless of the criterion used to establish an acquisition event. Residents in the two NHs with the highest prevalence of MRSA at baseline experienced the highest risk of MRSA acquisition (1.23 and 1.35 events per 1,000 resident-days) but the overall correlation between a facility’s baseline prevalence of MRSA and risk of acquisition was poor (spearman rank = 0.49, P = 0.33).

Conclusion: A large number of NH residents are colonized with MRSA and substantial numbers of acquisitions occur in these facilities. While risk of MRSA acquisition appeared to be higher in NHs with a very high prevalence of MRSA, there was poor overall correlation between these measures in our study suggesting that other facility characteristics contribute to the spread of MRSA in this setting. Subsequent studies should seek to better understand determinants of MRSA transmission in NHs.

Christopher Crnich, MD, PhD1,2,3, April Zehm, MD4, Simone Warrack, BS4, Megan Duster, BS MT (ASCP)4, Paul Drinka, MD5 and David Zimmerman, PhD6, (1)Division Of Infectious Diseases, University of Wisconsin School of Medicine and Public Health, Madison, WI, (2)William S. Middleton VA Hospital, Madison, WI, (3)Division Of Geriatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, (4)Division of Infectious Diseases, University of Wisconsin School of Medicine and Public Health, Madison, WI, (5)Division of Geriatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI, (6)Systems and Industrial Engineering, University of Wisconsin, Madison, WI

Disclosures:

C. Crnich, None

A. Zehm, None

S. Warrack, None

M. Duster, None

P. Drinka, None

D. Zimmerman, None

Findings in the abstracts are embargoed until 12:01 a.m. PST, Oct. 2nd with the exception of research findings presented at the IDWeek press conferences.