350. A comparison of Staphylococcus aureus incident nosocomial clinical culture rates among methicillin-resistant S. aureus carriers and non-carriers in the Veterans Affairs
Session: Poster Abstract Session: MRSA, MSSA, Enterococci
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C


It is unclear whether methicillin-resistant Staphylococcus aureus (MRSA) adds to or replaces the burden of disease caused by methicillin-susceptible strains (MSSA). Since the Veterans Affairs (VA) performed active surveillance testing for MRSA nasal carriage, we examined nosocomial MRSA and MSSA disease in two populations: MRSA surveillance test positive and negative on admission [MRSA(+) and MRSA(-)].


We used data from the Veterans Informatics and Computing Infrastructure to identify MRSA and MSSA clinical and surveillance isolates among acute care admissions screened for MRSA from Oct, 2007 through Sept, 2010. Admissions were included if a nares surveillance test was obtained within 12 hours of admission. An incident nosocomial clinical culture (INCC) was a positive clinical culture which occurred after the second calendar day of admission without preceding clinical isolation of the same organism within the past year. The INCC rate was denominated by appropriate patient days at risk (pd) for the outcome.


Data from 111 hospitals were analyzed. The MSSA overall INCC rate was 1.1/1000pd and declined from 1.2 to 1.0 between the first and last years of the study, respectively (-9.8%, p=0.001). When divided into MRSA(+) and (-) groups, there were non-significant declines in both groups (-11.2%, p=0.16; -4.7%, p=0.10; respectively). The overall MRSA INCC rate was 1.8/1000pd and declined from 2.0 to 1.5 (-23.0%, p<0.001). There was a non-significant decline in the MRSA(+) group (-5.4%, p=0.12) but a significant decline in the MRSA(-) group (-32.9% p<0.001). The Spearman's correlation of MRSA and MSSA INCC rates between facilities was 0.16 (p=0.09).


Our findings are consistent with the burden of MRSA being added to that of MSSA. Reasons for the apparent lack of anticipated competition between the two could be due to antibiotic use patterns or confounding. The significant decline in MRSA INCC rates among MRSA(-) individuals suggests decreased MRSA transmission through recent, VA-wide MRSA-targeted infection control efforts. The decline in MSSA INCC rates are also of interest and suggest a role for infection control and/or antibiotic use, although further investigation is necessary to elucidate the reasons.

Makoto Jones, MD, MS1, Jose Campo, MD1, Benedikt Huttner, MD, MS2, Karim Khader, PhD3, Christopher Nielson, MD, MPH4, Michael Rubin, MD, PhD5, Frederick Adler, PhD6 and Matthew Samore, MD7, (1)IDEAS Center, VA Salt Lake City Health Care System, Salt Lake City, UT, (2)Infection Control Program, Geneva University Hospitals, Geneva, Switzerland, (3)VA Salt Lake City Healthcare System, Salt Lake City, UT, (4)Office of Patient Care Services, Veterans Healthcare System, Reno, NV, (5)Internal Medicine, University of Utah School of Medicine, Salt Lake City, UT, (6)Mathematics, University of Utah, Salt Lake City, UT, (7)University of Utah School of Medicine, Salt Lake City, UT


M. Jones, None

J. Campo, None

B. Huttner, None

K. Khader, None

C. Nielson, None

M. Rubin, None

F. Adler, None

M. Samore, None

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