209 - Measuring Empiric Antibiotic Spectrum Patterns Across Space and Time

Background: Quantitative evaluation of antibiotic spectrum is an important, under-utilized metric in measuring antibiotic use (AU) and may assist antimicrobial stewards in identifying targets and strategy for intervention. We aimed to evaluate the spectrum of initial antibiotic choices by hospital location, day of the week, and time of day to understand if these factors may be associated with broad spectrum antibiotic choices.

Methods: We identified all admissions with antibiotic exposure in medical and surgical wards and critical care units in a tertiary academic medical center between July 1, 2014 and July 1, 2019. The antibiotic spectrum index (ASI), proposed by Gerber et al., is a numeric score based on the number of pathogens covered by a particular agent. We defined ASI for initial antibiotic choice as follows: ASI for each unique antibiotic administered within 24 hours of the first antibiotic administration was summed and assigned to the administration time of the first dose. We categorized time into four distinct categories: weekday days (Mon-Fri, 7AM-7PM), weekday nights, weekend days, and weekend nights. Weekend time was started 7pm Friday and ended 7AM Monday. We constructed heatmaps stratified by hospital location. Mann Whitney U tests were applied to evaluate differences in the distributions of ASI using weekday days as reference.

Results: Data included 90,455 unique antibiotic admissions with initial antibiotic starts in medical and surgical wards and critical care units. Patterns of ASI for initial antibiotic choice varied between unit locations and time (Figure 1 and 2). Mean and median ASIs for initial antibiotic choices were higher for medical ward and medical ICUs compared with surgical wards and surgical ICUs. Initial antibiotic choices had higher ASI during overnight hours for all units except the surgical ICU. Notable differences in ASI were identified between weekday and weekend prescribing for surgical units, while medical units had less extreme differences.

Conclusion: We observed a “weekend effect” across hospital units, most extreme in surgical wards. This observation may be due to differences in patient volume and rounding patterns. For example, hospitalist and critical care units have 7-day schedules while surgical wards are highly influenced by operating room schedules. Antimicrobial stewardship teams may use these data to identify strategies targeting the most opportune time and place to intervene on the spectrum of initial antibiotic choice