Pulsed-Field Gel Electrophoresis is a Useful Tool in the Monitoring of Methicillin-Resistant Staphylococcus Aureus Epidemic Outbreaks in the Intensive Care Unit

Abstract

We wished to determine how pulsed-field gel electrophoresis may be of use in monitoring methicillin-resistant Staphylococcus aureus (MRSA) outbreaks in the intensive care unit (ICU). A retrospective epidemiological analysis was conducted. All 27 ICU patients and 11 patients from other hospital wards from whom MRSA was isolated over a one year period were included in the study. Seventeen of the 27 ICU MRSA isolates were analysed by pulsed-field gel electrophoresis for clonality and compared with the 11 other hospital isolates genotypes over the same period. During three MRSA outbreaks, five MRSA genotypes were identified in ICU whilst the same five genotypes and three additional were found in the rest of the hospital. Pulsed-field gel electrophoresis analysis was useful in identifying clonality of ICU MRSA infections and establishing that they were imported from hospital wards, rather than arising de novo in ICU. We were further able to identify clonal clusters within the unit linked by temporal and geographical proximity, suggestive of cross-infection. Pulsed-field gel electrophoresis typing might be additionally useful in tracing the source of human and/or environmental factors if a genotype were persistently identified.