Background: Our retrospective investigation of methicillin-resistant Staphylococcus aureus (MRSA) infection at a hospital in Japan around 2007 suggested dissemination of community-associated MRSA (CA-MRSA) strains among healthy students in a Japanese boarding school, which frequently caused skin disease and exhibited the same antibiogram patterns. Methods: Active surveillance of skin diseases for 6 months after May 2008, examination of MRSA carriage in selected high-risk groups, and investigation of their life circumstances, including environmental cultures, were conducted in the school. Furthermore, we strengthened hygiene practices and improved recognized risk factors from November 2008 and observed the occurrence of skin diseases and MRSA carriage rate for the evaluation of infection controls. Results: We identified 21 patients with skin diseases in whom MRSA strains were isolated. MRSA colonization rates in 3 selected groups ranged from 7.6% to 36.6%. The rates of both skin disease and MRSA carriage decreased significantly after infection controls were introduced. Genetic analysis revealed a main dissemination of a PVL-positive SCCmec IVc clone (41/47 isolates in total), presenting as a different pulsed-field type than USA300. Conclusion: This first report of a PVL-positive CA-MRSA outbreak in Japan demonstrates systematic management of dissemination by conducting surveillance in a closed community.
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