Characteristics of polyclonal endemicity of Pseudomonas aeruginosa colonization in intensive care units - Implications for infection control

We investigated the endemicity of Pseudomonas aeruginosa in intensive care units (ICUs) through analyses of surveillance cultures (from the rectum, st omach, oropharynx, and trachea; n = 1,089), and clinical cultures (n = 2,39 3) from 297 consecutive patients. Multiple isolates of P. aeruginosa (n = 3 53) were genotyped. Variables associated with acquisition of respiratory tr act colonization (RTC) were tested in a risk factor analysis. The mean dail y prevalence of colonization was 34%. On admission, 22 patients had intesti nal colonization and 13 had RIG. Twenty patients acquired colonization in t he intestinal and 24 in the respiratory tract. Forty-four different genotyp es were found; 38 (86%) were isolated from individual patients only. In all , 37 patients had RTC with a total of 38 genotypes: 13 (34%) were colonized on admission, 9 (24%) acquired RTC with a novel genotype during a stay in the ICU, five (13%) acquired colonization from their intestinal tract and t hree (8%) were colonized via cross-acquisition. In eight patients (21%), no route could be demonstrated for colonization. Antibiotics providing P. aer uginosa with a selective growth advantage were associated with acquired RTC . Endemicity of colonization with P. aeruginosa is characterized by polyclo nality, and seems to be maintained by continuous admittance of colonized pa tients and selection pressure from antibiotics rather than by cross-acquisi tion.