Factors Associated with Relative Rates of Antibiotic Resistance in Pseudomonas aeruginosa Isolates Tested in Clinical Laboratories in the United States from 1999 to 2002

ABSTRACT For the period from 1999 to 2002 in the United States, the in vitro susceptibilities of 52,637 Pseudomonas aeruginosa isolates to 10 antimicrobial agents were evaluated. The isolates were from 29 laboratories, 11 of which participated in The Surveillance Network for four consecutive years. Isolates were collected from adult patients (≥18 years of age) in intensive care units (ICU), non-ICU inpatients, nursing home patients, and outpatients; data were analyzed to evaluate factors, such as year of isolation, patient age group, isolate specimen source, and patient type (hospitalized patients [ICU, non-ICU, or nursing home] or outpatients). Rates of resistance for the 4-year period were highest for isolates from patients in ICU and 18- to 39-year-old patients and for isolates from the lower respiratory tract. Resistance decreased with age. Resistance was lowest in isolates from outpatients, in isolates from ≥70-year-old patients, and from specimens from the upper respiratory tract. Multidrug resistance (MDR) (resistance to three or more antimicrobial agents) accounted for 24.9% of all isolates. The MDR rate was highest in isolates from patients in nursing homes (29.9%) and ICU (29.5%).