ANALYSIS OF AN OUTBREAK OF NON-PHAGE-TYPABLE METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS BY USING A RANDOMLY AMPLIFIED POLYMORPHIC DNA ASSAY

A cluster of methicillin-resistant Staphylococcus aureus (MRSA) infect ions among patients on an intensive care unit (ICU) was detected by ro utine infection control surveillance, In the period from 5 January to 22 June 1995, 10 patients on the ICU and a further 6 patients (5 on on e ward that had received colonized patients transferred from the ICU) were affected by MRSA strains with the same antibiotic susceptibility patterns, Seven (44%) of these 16 colonized patients developed MRSA ba cteremia, MRSA isolates with the same characteristics were also found on the hands of one member of the ICU staff, The, isolates were untype able by phage typing, but 15 of 17 outbreak strains analyzed genetical ly had identical randomly amplified polymorphic DNA (RAPD) and pulsed- field gel electrophoresis (PFGE) profiles, A single strain of MRSA tha t was nontypeable by phage typing and that was isolated on the ICU on 1 January and six nontypeable and epidemiologically unrelated MRSA iso lates all had RAPD profiles distinct from that of the outbreak strain, Implementation of strict infection control measures stopped the furth er spread of MRSA on the ICU, the affected general ward, and seven oth er wards that received MRSA carriers from the ICU, Although nontypeabl e by phage typing and not previously recognized as an epidemic strain, this strain of MRSA was readily transmissible and highly virulent. RA PD typing was found to be a simple, rapid, and effective method for th e epidemiological investigation of this outbreak, and performance of t yping by this method was simpler and less time-consuming than that of typing by PFGE, RAPD typing may have more general application for the study of S. aureus infections in hospitals.