Background: The standardized antimicrobial administration ratio (SAAR) compares each hospitals observed to predicted days of antimicrobial therapy. However, confusion exists about how hospital-level, seasonal, and hospital-peer-based variations in antibiotic use might impact an institutions SAAR. We characterized the impact of each of these 3 types of variation on predicted SAARs utilizing local NHSN data.
Methods: Analysis of antibiotic consumption data from an academic medical center in Chicago, IL was conducted. SAAR and antimicrobial days per 1000 days present (AD/1000DP) were compiled in monthly increments from 2014 to 2016. Antimicrobial consumption was aggregated and classified into agent categories according to NHSN criteria. Month-to-month changes in both the SAAR and AD/1000DP were evaluated. Azithromycin AD/1000DP from 2012 through 2017 were explored for seasonal variation as defined as >20% increase in AD/1000DP from each quarter to the overall mean AD/1000DP for all months. A simulation was performed to explore the potential effect of seasonality on the SAAR. Demographic covariates within the SAAR model were altered while holding constant observed antibiotic use; thus we were able to observe the potential impact of demographics. Finally, a simulation explored the effect of altered consumption at other hospitals on a local institutions SAAR.
Results: Across all antibiotic agent categories for both ICU (n=4) and general wards (n=4), the average matched-month percent change in AD/1000DP was highly predicted and correlated with the corresponding change in SAAR (Figure 1, Pearsons r = 0.99). The monthly mean±SD AD/1000DP was 235.0 (range 47.2-661.5), and the mean±SD SAAR was 1.09±0.26 (range 0.79-1.09) across the NHSN antibiotic agent categories. Five quarters were found to have seasonal variation in AD/1000DP for azithromycin (Figure 2). Simulations demonstrated that changing antimicrobial usage at comparator hospitals does not impact the local SAAR, and seasonal variation may cause fluctuating SAARs.
Conclusion: Month-to-month changes in the SAAR mirror monthly changes in an institutions AD/1000DP. Seasonal variation can impact the SAAR, and the effect changing peer hospital antibiotic consumption is not currently captured by the SAAR methodology.
J. Liu, Merck: Grant fund from Merck , Research grant .
D. Aljefri, None
M. Postelnick, None
S. Sutton, None
T. Zembower, None
D. Martin, Syneos Health: Employee , Salary . GlaxoSmithKline: Independent Contractor , Salary .
G. Pais, None
C. Cruce, None
M. H. Scheetz, Merck & Co., Inc.: Grant Investigator , Grant recipient . Bayer: Consultant , Consulting fee .
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