Outbreak of Pseudomonas aeruginosa infections in a surgical intensive care unit: probable transmission via hands of a health care worker.

Pseudomonas aeruginosa was isolated from nine patients (16.2 isolations/1,000 patient-days) in a surgical intensive care unit during an outbreak in November 1990; this rate of isolation was three times higher than that noted previously on this unit. Three patients were infected with the same strain, as defined by identical serotypes, pyocin types, and contour-clamped homogeneous electric field (CHEF) electrophoresis patterns of digested genomic DNA. The hands of 80 health care workers were cultured, and a strain of P. aeruginosa identical to that infecting the three patients was isolated from the hands of a nurse providing care to all three. Environmental surfaces, medical devices, and ward stock supplies were cultured; none of these cultures yielded this strain. No clusters of infection with this strain or other strains of P. aeruginosa were observed after compliance with hand-washing and universal precautions was reemphasized. Thus this outbreak was linked to the carriage of P. aeruginosa on the hands of a health care worker. It could not be determined definitively whether this carriage was the source of the cluster or a consequence of it. However, the geographic and temporal clustering of carriage with an outbreak due to a strain of an apparently identical molecular type underlines the importance of routine hand washing between contacts with different patients.