Epidemiological study of an outbreak of Serratia marcescens in a haemodialysis unit

Twenty-three isolates of Serratia marcescens were isolated over a 10-month period from the blood and arteriovenous shunt sites of patients undergoing haemodialysis in an artificial kidney unit. Surveillance measures performed on the equipment, sterile materials, environment and personnel of this unit yielded Serratia from the air conditioner and one of the dialysis units. The isolates from the patients and dialyser unit were pigmented and had an identical biochemical profile, antibiograms, phage typing pattern and O serotype. The isolate from the air conditioner, though of the same biotype, had a different phage and serotype. It was concluded that the dialyser was the 'common source' and that the organism was persisting in the machine in spite of recommended sterilization procedures being implemented.