Pseudomonas aeruginosa, Staphylococcus aureus, & Fluoroquinolone
Few long-term multicenter investigations have evaluated the relationships between aggregate antimicrobial drug use in hospitals and bacterial resistance. We measured fluoroquinolone use from 1999 through 2003 in a network of US hospitals. The percentages of fluoroquinolone-resistant Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) were obtained from yearly antibiograms at each hospital. Univariate linear regression showed significant associations between a hospital's volume of fluoroquinolone use and percent resistance in most individual study years (1999–2001 for P. aeruginosa, 1999–2002 for S. aureus). When the method of generalized estimating equations was used, a population-averaged longitudinal model incorporating total fluoroquinolone use and the previous year's resistance (to account for autocorrelation) did not show a significant effect of fluoroquinolone use on percent resistance for most drug-organism combinations, except for the relationship between levofloxacin use and percent MRSA. Theecologic relationship between fluoroquinolone use and resistance is complex and requires further study.

Antimicrobial drug resistance in bacterial pathogens is of national and international concern . Although use of antimicrobial agents is accepted as a major driving force behind the spread of resistance,the nature of this relationship is complex . Two problematic nosocomial pathogens are Pseudomonas aeruginosa and Staphylococcus aureus; both often express multidrug resistance. A number of case-control studies at individual hospitals have identified fluoroquinolone use asa risk factor for acquisition of fluoroquinolone-resistant P. aeruginosa and methicillin-resistant S. aureus (MRSA). While outcomes for individual patients are most important from a clinical point of view, an ecologic perspective is also useful to assess the relationship of aggregate antimicrobial drug use to aggregate measures of bacterial resistance. Ecologic investigations across multiple hospitals have reported significant correlations between fluoroquinolone use and percent resistance for MRSA and P. aeruginosa . However, these studies have primarily focused on teaching institutions,used drug expenditure data rather than hospital billing records as a measure of use, or were conducted over a limited time span. We measured fluoroquinolone use as well as the percentages of MRSA and fluoroquinolone-resistant P.aeruginosa across 24 US hospitals during a 5-year period. The Purpose of this observational study was to determine if volume of aggregate fluoroquinolone use in individual hospitals and bacterial resistance in individual years and during the entire study period are associated.