AN OUTBREAK OF AN UNUSUAL STRAIN OF SERRATIA-MARCESCENS IN 2 DUBLIN HOSPITALS

We describe a serious outbreak of infection caused by a strain of Serr atia marcescens in two Dublin hospitals which occurred over an 11 week period and affected a total of 15 patients. A contaminated bed-pan ma cerater in the Intensive Care Unit of one hospital was identified as t he possible source of infection and spread of the organism probably oc curred via hand transmission by hospital personnel and via patient tra nsfer to a second hospital. All isolates of S. marcescens involved in the outbreak had the same antimicrobial susceptibility pattern, with r educed susceptibility to gentamicin, cefotaxime and ciprofloxacin. Epi demiological typing revealed that the strains of S. marcescens isolate d in the outbreak were of an uncommon serotype, O21:K14, and using pul sed-field gel electrophoresis, XbaI DNA macrorestriction profiles clus tered at 90% similarity. The DNA patterns of the outbreak strain were also highly similar to S. marcescens isolates of the same serotype rec overed from a separate Dublin hospital during the same time period as the outbreak described here. In addition, the isolates clustered at 82 % similarity with strains of the same serotype from a retrospective co llection of S. marcescens isolates from various hospitals in the Dubli n area, indicating that these may be genetic variants of the same stra in. Although the outbreak was brought under control following implemen tation of infection control measures, a significant number of similar O:21 isolates of S. marcescens have since been identified in four Dubl in hospitals. These results suggest the unique spread of a single stra in of S. marcescens in Dublin hospitals.