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.