Assessment of bacterial cross-transmission as a cause of infections in patients in intensive care units.

The prevalence of possible cross-transmission of selected bacteria (Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas aeruginosa, Staphylococcus aureus, and enterococci) among infected patients was evaluated in five intensive care units (ICUs) over 6 months. A total of 284 isolates from clinical specimens were typed by plasmid profile analysis (E. coli, K. pneumoniae, and E. cloacae), restriction endonuclease analysis of plasmid DNA (S. aureus), and/or pulse-field gel electrophoresis of chromosomal DNA (P. aeruginosa, enterococci, S. aureus, and other bacteria without plasmid DNA). By typing criteria, only 13% of the 177 isolates obtained after > 2 days in an ICU were classified as possibly cross-transmitted. Many patients whose cultures yielded bacteria of an identical type may have been the sources rather than the recipients of these organisms. Episodes of possible cross-transmission were scattered among all ICUs, usually affected only two patients, and were associated with most bacterial species. These data suggest that endemic bacterial cross-transmission in ICUs is relatively infrequent and that cross-transmitted bacteria are not common causes of endemic ICU-related nosocomial infections.