Extensive intra-hospital spread of a methicillin-resistant Staphylococcal clone

Objective: Infection by antibiotic-resistant bacteria can pose serious complications to the therapy of cancer patients. The authors introduced DNA fingerprinting techniques for tracking methicillin-resistant Staphylococcus aureus (MRSA) clones recovered at a central cancer hospital of Lisbon (Instituto Portugues de Oncologia) with the purpose of making an inventory of the MRSA clones endemic during 1995, and compared them with the outbreak- related clones of 1993. Design: A small group (6 strains) of epidemiologically related MRSA isolated during a suspected outbreak in 1993 and all consecutive single-patient isolates of MRSA (34 strains) recovered between January and November of 1995 from infected patients and health care personnel were characterized using DNA probes and pulsed-field gel electrophoresis. Results: The six 1993 strains and more than half of all 1995 isolates, including those recovered from the health care personnel, showed DNA fingerprints characteristic of the 'Iberian MRSA,' a multiresistant clone widespread in Portuguese and Spanish hospitals. Four patients were infected by another MRSA clone previously seen only in hospitals in Brazil. Conclusion: The epidemic Iberian clone was among the index cases involved with the MRSA outbreak in 1993, and this was found to be endemic in a follow- up survey conducted in 1995, colonizing health care personnel and spreading to most hospital wards. A few isolates of another epidemic clone, the Brazilian MRSA, also were detected among 1995 isolates. A better understanding of the mechanism(s) of epidemicity of these rapidly spreading clones is urgently needed.