FOOD-INITIATED OUTBREAK OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS ANALYZED BY PHENOTYPING AND GENOTYPING

An outbreak of methicillin-resistant Staphylococcus aureus (MRSA) invo lving 27 patients and 14 health-care workers (HCW) was studied. The ou tbreak started in the hematology unit of the University Hospital Rotte rdam, Dijkzigt, The Netherlands, and spread to the surgical unit. Twen ty-one patients (77.8%) developed clinical disease, and five died, Sub sequently, MRSA was detected in food and in the throat of one of the H CW who prepared food for hematology patients. Food contaminated by an HCW most likely caused the first case of MRSA septicemia. This route o f transmission has not been described before. The outbreak strain was probably transmitted to the surgical unit by a colonized nurse, where it caused an explosive outbreak Airborne MRSA transmission played an i mportant role in disseminating the organism, The outbreak was controll ed within 6 months by intensifying surveillance, temporarily closing t he affected wards, treating carriers, and instituting an MRSA nard out side the hospital, Phage typing, insertion sequence probing, protein A gene typing, and DNA fingerprinting by PCR revealed that all outbreak -related isolates were identical. By pulsed-field gel electrophoresis, all but one of the outbreak-related isolates were determined to be id entical. Protein A gene typing identified numerous (11) repeat units i n all outbreak-related isolates, which supports the suggestion that th e outbreak strain may have been more virulent and more transmissible t han other MRSA strains, Pheno- and genotyping studies underlined the v alue of DNA fingerprinting methods for investigation of MRSA epidemiol ogy, Optimal discriminatory power was achieved by combining the result s of four genotyping methods.