Acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically-ill medical patients: role of colonization pressure and antibiotic exposure (Critical Care)

IntroductionThe objective of this work is to investigate the risk factors for the acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically-ill patients taking into account colonization pressure. Methods: Prospective cohort study in an 8-bed medical intensive care unit during a 35-month period. Nasopharyngeal and rectal swabs and respiratory secretions were obtained within 48 h of admission and thrice weekly thereafter. During the study, a policy of consecutive mixing-cycling periods of three classes of antipseudomonals was operative in the unit. Results: Out of 850 patients admitted for ≥3 d, 751 (88.3%) received an antibiotic of which 562 (66.1%) was an antipseudomonal. Sixty-eight (8%) patients carried P. aeruginosa on admission and from the remaining 782, 104 (13%) acquired at least one strain of P. aeruginosa during their stay. Multivariate analysis selected shock (OR 2.1; 1.2-3.7), intubation (OR 3.6; 1.7-7.5), enteral nutrition (OR 3.6;1.8-7.6), parenteral nutrition (OR 3.9; 1.6- 9.6), tracheostomy (OR 4.4; 2.3-8.3) and colonization pressure >0.43 (OR 4; 1.2-5) as independently associated with the acquisition of P. aeruginosa while exposure to fluoroquinolones for >3 days (OR 0.4; 0.2-0.8) was protective. In the whole series, prior exposure to carbapenems was independently associated with carbapenem resistance while prior amikacin predicted piperacillin-tazobactam, fluroroquinolone and multiple-drug resistance. Conclusions: In critical care settings with a high rate of antibiotic use, colonization pressure and non-antibiotic exposures may be the crucial factors for P. aeruginosa acquisition while fluoroquinolones may actually decrease it. For the acquisition of strains resistant to piperacillin-tazobactam, fluroquinolones and multiple drugs, exposure to amikacin may be more relevant than previously recognized.