Outbreak caused by tobramycin-resistant Pseudomonas aeruginosa in a bone marrow transplantation unit

Between May and August 1995, 5 patients in a bone marrow transplantation (B MT) ward developed bacteremia caused by Pseudomonas aeruginosa resistant to tobramycin (TRPA). Previously, isolates of TRPA had been limited to patien ts who were treated in 1 intensive care unit (ICU) of this tertiary care te aching hospital in Helsinki, Finland. To study whether the outbreak was cau sed by a single or multiple strains of P. aeruginosa, 102 isolates of TRPA from clinical samples obtained from different hospital units and 22 isolate s obtained from the hospital environment were characterized by pulsed-field gel electrophoresis. All isolates from hematological patients produced 1 u nique fragment pattern, which was also isolated from 3 ICU patients before the BMT ward outbreak began as web as from 5 shower heads in the BMT ward. The outbreak in the BMT ward was successfully controlled by eradicating the probable environmental source - contaminated hand showers - but the endemi c infections continued in the ICU.