Methods: A retrospective ecological study of P. aeruginosa isolates and carbapenem usage at the VA St. Louis Health Care System (HCS) was conducted. Data on usage of all carbapenems, measured in defined daily doses (DDD), and all non-duplicate Pseudomonal isolates with associated antibiotic susceptibility testing profiles were collected from January 1, 2008 through December 31, 2014. Multidrug resistance was defined as resistance to two or more groups of antibiotics, and MDR rates were compiled and determined based on susceptibilities. The primary outcome was to determine if a correlation between total carbapenem usage at the VA St. Louis HCS and the incidence of MDR Pseudomonal isolates exist. Secondary outcomes included evaluating for correlations between imipenem usage, meropenem usage, total antipseudomonal carbapenem usage, total ertapenem usage, ertapenem treatment use, and ertapenem for surgical prophylaxis and rates of MDR Pseudomonas.
Results: A total of 1268 isolates were evaluated. From 2008 to 2014, the rates of MDR Pseudomonas were 18%, 16%, 17%, 17%, 10%, 13%, and 25% respectively. The total institutional carbapenem use, in DDD, was 634, 733, 1162, 1320, 1159, and 1588 over the same period of time. There was not a significant correlation between DDD of all carbapenems and rates of MDR Pseudomonas (R2= 0.452; P=0.308). Additionally, no significant correlations were observed for the other carbapenem categories.
Conclusion: In this small ecological evaluation, no correlation between institutional carbapenem usage and rates of MDR Pseudomonas were observed.
R. P. Moenster, None