Subtyping of Shigella sonnei for tracing nosocomial transmission.

Nosocomial transfer of Shigella spp. occurred between two patients sharing the patient room and toilet in a ward for internal medicine. Both patients had travelled abroad shortly before the onset of illness. Based on the epidemiology of Shigella sonnei strains imported into Finland, nosocomial infection was strongly suspected. The isolates of S. sonnei were subtyped using ribotyping, plasmid analysis and antibiotic resistance patterns. The greatest discrimination between the strains was achieved by ribotyping. The results of the typing scheme confirmed the nosocomial transmission of S. sonnei. The outbreak did not spread further within the ward. The importance of isolation of a patient with diarrhoea in a hospital setting is emphasized.