Does Size Matter? Variation in Antimicrobial Use in the Largest not for Profit Health System in the United States

Background: Inappropriate antimicrobial use is associated with increased cost, significant patient harm, and infection control challenges. We assessed antimicrobial use in a system of 69 hospitals located in 15 states.

Methods: We evaluated systemic antimicrobial acquisition cost of 69 hospitals from 2010 to 2012. In addition to antimicrobial cost per patient day, daily defined dose (DDD) of systemic broad spectrum antimicrobial classes (quinolone, carbapenem, piperacillin/tazobactam, streptogramin, tetracycline, macrolide, lipopeptide, oxazolidinone, 3rd and 4th generation cephalosporins, azole, polyene, echinocandin) were calculated. We also compared hospital volume using annual patient days, case mix index (CMI) and cost categories.

Results: The 3 years included 9,456,762 patient-days, with 4,962,072 DDDs, with a cost of $124,222,245. There were no significant changes for individual hospitals in mean antimicrobial use of targeted broad-spectrum agents (DDD 0.77, 0.74, 0.8) or cost ($14.8, $14.2, $13.8) per patient-days for paired comparisons for 2010, 2011, and 2012 respectively. In 2012, hospitals with less than 50,000 patient-days were more likely to use antimicrobials (DDD>1: 14/41, 34.1%; DDD 1 or less: 27/41, 65.9%) than hospitals with >50,000 patient-days (DDD>1: 2/28, 7.1%; DDD 1 or less: 26/28, 92.9%; p=0.009). Lower antimicrobial cost hospitals tended to have continued cost reduction during the 3 years, in contrast to those with baseline of high cost (Table). In addition, hospitals with CMI 1 or less had higher cost ($17.7±11.3) compared to hospitals with CMI >1 (12.7±5.4; p=0.024).

Conclusion: Our findings suggest that hospitals smaller in size and lower CMI had more antimicrobial use than large hospitals and higher CMI. The analysis provides us with valuable information for further evaluation and process standardization to achieve antimicrobial stewardship across the hospitals within our system.

Table: Comparing mean antimicrobial use of targeted antimicrobial agents and cost for 69 hospitals between 2010 and 2012 (paired T-test).

	2010	2011	P value (2010 to 2011)	2012	P value (2010 to 2012)
Utilization per patient day
DDD 1 or less (n=53)	0.53	0.55	0.73	0.54	0.85
DDD>1 (n=16)	1.57	1.34	0.55	1.65	0.88
Cost per patient-day ($)
<$10 (n=20)	$8.61	$7.96	0.2	$6.85	0.06
$10-20 (n=39)	$16.27	$15.07	0.15	$14.05	0.02
>$20 (n=10)	$21.29	$23.64	0.1	$26.52	0.06