Decreased Prevalence of -Positive Methicillin-Resistant in Hospitalized Patients in Tokyo, Japan.

Presence of methicillin-resistant (MRSA) strains carrying plasmid-borne multidrug efflux pump-encoding gene, , is a serious issue for infection control in hospitals, because they can survive hand hygiene. The genes are divided into five subtypes: , , , , and . The aim of this study was to investigate the prevalence and risk factors of hospitalized patients infected by respective -positive MRSA strains between 2010 and 2016 in Tokyo, Japan. Of the 600 total MRSA strains observed, the -positive strains constituted 19.8% (199 isolates), of which 56.8% (113 isolates), 28.6% (57 isolates), and 14.6% (29 isolates) were classified as , , and -positive strains, respectively. The prevalence of -positive MRSA strains significantly decreased from July 2010 to June 2011 (34.0%) to July 2015 to May 2016 (5.3%) ( < 0.05). When staphylococcal cassette chromosome (SCC) types of the respective -positive strains were determined, 81.4% of the -positive strains were classified into SCC type II, which has recently been decreasing in hospital-acquired MRSA in Japan. Risk factor analysis showed that there were no specific clinical departments associated with the presence of -positive strains. Our findings suggest that change in the MRSA clonal lineages impact to decrease the prevalence of -positive strains in Japanese hospitals.