Acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically ill medical patients: role of colonization pressure and antibiotic exposure.
BACKGROUND
The objective of this work was 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
We conducted a 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 hours of admission and thrice weekly thereafter. During the study, a policy of consecutive mixing and cycling periods of three classes of antipseudomonal antibiotics was followed in the unit.


RESULTS
Of 850 patients admitted for ≥ 3 days, 751 (88.3%) received an antibiotic, 562 of which (66.1%) were antipseudomonal antibiotics. A total of 68 patients (8%) carried P. aeruginosa upon admission, and among the remaining 782, 104 (13%) acquired at least one strain of P. aeruginosa during their stay. Multivariate analysis selected shock (odds ratio (OR) = 2.1; 95% confidence interval (CI), 1.2 to 3.7), intubation (OR = 3.6; 95% CI, 1.7 to 7.5), enteral nutrition (OR = 3.6; 95% CI, 1.8 to 7.6), parenteral nutrition (OR = 3.9; 95% CI, 1.6 to 9.6), tracheostomy (OR = 4.4; 95% CI, 2.3 to 8.3) and colonization pressure >0.43 (OR = 4; 95% CI, 1.2 to 5) as independently associated with the acquisition of P. aeruginosa, whereas exposure to fluoroquinolones for >3 days (OR = 0.4; 95% CI, 0.2 to 0.8) was protective. In the whole series, prior exposure to carbapenems was independently associated with carbapenem resistance, and prior amikacin use predicted piperacillin-tazobactam, fluoroquinolone 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, whereas fluoroquinolones may actually decrease its likelihood. For the acquisition of strains resistant to piperacillin-tazobactam, fluoroquinolones and multiple drugs, exposure to amikacin may be more relevant than previously recognized.
Department of Infectious Diseases, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. fncobos@clinic.ub.es.
Nazaret
N
Cobos-Trigueros
ISGlobal, Barcelona Center for International Health Research (CRESIB), Hospital Clínic, University of Barcelona, Barcelona, Spain. marsole04@gmail.com.
Mar
M
Solé
Medical Intensive Care Unit, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. pcastro@clinic.ub.es.
Pedro
P
Castro
Department of Internal Medicine, University Hospital of Salamanca, Institute of Biomedical Research of Salamanca (IBSAL), Salamanca, Spain. jltorrest@gmail.com.
Jorge Luis
JL
Torres
Medical Intensive Care Unit, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. chernan1@clinic.ub.es.
Cristina
C
Hernández
Medical Intensive Care Unit, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. marianorinaudo@gmail.com.
Mariano
M
Rinaudo
Medical Intensive Care Unit, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. sfernanm@clinic.ub.es.
Sara
S
Fernández
Department of Infectious Diseases, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. asoriano@clinic.ub.es.
Álex
Á
Soriano
Medical Intensive Care Unit, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. nicolas@clinic.ub.es.
José María
JM
Nicolás
Department of Infectious Diseases, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. jmensa@clinic.ub.es.
Josep
J
Mensa
ISGlobal, Barcelona Center for International Health Research (CRESIB), Hospital Clínic, University of Barcelona, Barcelona, Spain. jvila@clinic.ub.es.|Department of Clinical Microbiology, Hospital Clinic, School of Medicine, University of Barcelona, Barcelona, Spain. jvila@clinic.ub.es.
Jordi
J
Vila
Department of Infectious Diseases, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), University of Barcelona, Barcelona, Spain. jamarti@clinic.ub.es.
José Antonio
JA
Martínez
D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D015331:Cohort Studies; D015169:Colony Count, Microbial / Q000379:methods; D003422:Critical Care / Q000639:trends; D016638:Critical Illness / Q000628:therapy; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects*; D005260:Female; D006801:Humans; D007362:Intensive Care Units / Q000639:trends; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D011446:Prospective Studies; D011552:Pseudomonas Infections / Q000175:diagnosis / Q000188:drug therapy; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000302:isolation & purification*
D000900:Anti-Bacterial Agents