Nosocomial bacteriuria: a prospective study of case clustering and antimicrobial resistance.

To investigate the role of cross-infection in nonepidemic nosocomial bacteriuria in a large, university-affiliated hospital, we identified in adult patients admitted over an 11-week period all cases caused by organisms of the same genus, species, and antimicrobial susceptibility and clustered by date of onset and hospital ward. Further laboratory studies were conducted to verify clustering. Among the 3452 patients studied, 194 cases of nosocomial bacteriuria were identified; 49 appeared clustered by epidemiologic evidence. Additional laboratory tests verified clustering in 30 cases (15.5%). We found that 90% of clustered and 76% of nonclustered cases had had previous urinary catheterization; Pseudomonas aeruginosa, Serratia marcescens, and Citrobacter freundii often caused clustered infection while Escherichia coli predominated in nonclustered cases; and resistance to gentamicin, sulfathiazole, and carbenicillin was significantly greater for pathogens from clustered cases than for nonclustered ones. This increased resistance emphasizes the need to prevent cross-infection, even in the absence of epidemics.