Risk factors for and impact of infection or colonization with aztreonam-resistant Pseudomonas aeruginosa

OBJECTIVE. To identify risk factors for infection or colonization with aztreonam-resistant Pseudomonas aeruginosa and examine the impact of this organism on mortality. DESIGN. A case-control study was performed to identify risk factors for infection or colonization with aztreonam-resistant P. aeruginosa. A cohort study was subsequently performed to examine the impact of aztreonam resistance on outcomes. SETTING. A tertiary referral center in southeastern Pennsylvania. PARTICIPANTS. Inpatients with a clinical culture positive for P. aeruginosa between January 1, 1999, and December 31, 2000. RESULTS. Of 720 P. aeruginosa. isolates, 183 ( 25.4%) were aztreonam-resistant and 537 ( 74.6%) were aztreonam susceptible. In a multivariable model, prior fluoroquinolone use ( adjusted odds ratio [ aOR], 1.81 [ 95% confidence interval {CI}, 1.17-2.80]), prior use of an antianaerobic agent ( aOR, 1.56 [ 95% CI, 1.06-2.29]), and renal insufficiency ( aOR, 1.59 [ 95% CI, 1.10-2.29]) were associated with infection or colonization with aztreonam-resistant P. aeruginosa, while older age ( aOR, 0.98 [ 95% CI, 0.97-0.99] per year of age) was negatively associated with infection or colonization with this organism. In-hospital mortality was higher among subjects infected or colonized with aztreonam-resistant P. aeruginosa, compared with those who were infected or colonized with aztreonam-susceptible P. aeruginosa ( 25.7% vs 16.8%; P = .009), but in multivariable analysis, no significant association was found between infection or colonization with aztreonam-resistant P. aeruginosa and mortality. CONCLUSIONS. Curbing the use of fluoroquinolones and antimicrobials with antianaerobic activity may be an effective strategy to limit the emergence of aztreonam-resistant P. aeruginosa.