1143. Effects of initial anti-methicillin-resistant Staphylococcus aureus (MRSA) antibiotics on nosocomial MRSA acquisition and clinical cultures
Session: Poster Abstract Session: MRSA/VRE Epidemiology
Friday, October 9, 2015
Room: Poster Hall
Background: Recent studies of methicillin-resistant Staphylococcus aureus (MRSA) infections have reported decreased incidence in diverse settings around the world, usually in the setting of infection control interventions. Concurrently, vancomycin use has also been increasing. We investigated the possibility that initial anti-MRSA antibiotic (anti-MRSA) use may have direct protective effects on nosocomial MRSA acquisition and infection.

Methods: We used retrospective data from a cohort of patients hospitalized in the Veterans Health Administration from October 2007 through September 2010 who had no MRSA-positive cultures at admission. We used a propensity score-based matching weights analysis to compare patients who received initial anti-MRSA to those who did not with respect to inpatient MRSA acquisition and nosocomial clinical culture outcomes. Anti-MRSA exposure was defined as receipt within the first two days of admission. Hospital and admission characteristics, other antibiotics given at admission, principal diagnostic categories, and comorbidities (>1 ICD-9 code in the past year) were included to adjust for the propensity of exposure. MRSA acquisition was defined as a negative screening test followed by a positive. MRSA culture was defined as a first positive MRSA culture after day 3 of admission. To focus on nosocomial infections as a result of progression, the model for MRSA nosocomial culture was restricted to admissions with positive screens.

Results: The crude odds ratio of MRSA acquisition given anti-MRSA was 1.3 (95%CI 1.2-1.5). The same for MRSA nosocomial culture was 1.2 (95%CI 1.0-1.4). Matching weights resulted in a decrease in the standardized difference to less than 0.1 in all included covariates. The adjusted odds ratios for MRSA acquisition and culture were 1.2 (95%CI 1.0-1.4) and 1.0 (95%CI 0.8-1.3), respectively.

Conclusion: Initial anti-MRSA use does not appear to impact nosocomial MRSA acquisition and late cultures. However, because we did not differentiate between brief or prolonged courses, this analysis was akin to an intention-to-treat analysis on the effects of a strategy of initial anti-MRSA use. Since this tends to dilute estimates of on-anti-MRSA effects, further investigation is necessary to elucidate on-anti-MRSA effects.

Makoto Jones, MD, MS1,2, Jenny Teng, MS3, Benedikt Huttner, MD, MS4, Vanessa Stevens, PhD1, Richard E. Nelson, PhD1, Karim Khader, PhD1, Michael Rubin, MD, PhD, FIDSA5, Christopher Nielson, MD, MPH6, Brian Sauer, PhD5 and Matthew Samore, MD, FSHEA7, (1)Ideas Center, VA Salt Lake City Health Care System, Salt Lake City, UT, (2)Department of Medicine, University of Utah School of Medicine, Salt Lake City, UT, (3)Epidemiology, VA Salt Lake City Health Care System, Salt Lake City, UT, (4)Infection Control Program, Geneva University Hospitals, Geneva, Switzerland, (5)Internal Medicine, University of Utah School of Medicine, Salt Lake City, UT, (6)Office of Patient Care Services, Veterans Healthcare System, Reno, NV, (7)University of Utah School of Medicine, Division of Epidemiology, Salt Lake City, UT


M. Jones, None

J. Teng, None

B. Huttner, None

V. Stevens, None

R. E. Nelson, None

K. Khader, None

M. Rubin, None

C. Nielson, None

B. Sauer, None

M. Samore, None

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