Molecular epidemiological surveillance of methicillin-resistant Staphylococcus aureus in a Hiroshima community hospital in 2002.

*Corresponding author: Fax: +81-3-3202-7181, E-mail: tkirikae@ ri.imcj.go.jp Methicillin-resistant Staphylococcus aureus (MRSA) is a major hospital-acquired pathogen in institutions including community hospitals with relatively small numbers of beds (1,2). Molecular epidemiological surveillance using restriction fragment-length polymorphisms of genomic DNA employing pulsed-field gel electrophoresis (PFGE) is essential for assessment of hospital infection controls (3). The present surveillance was conducted in a hospital in Hiroshima. The hospital had two wards totaling 120 beds. The subjects included 100 inpatients and 111 medical staff members present in the hospital in February 2002. A total of 39 MRSA isolates were obtained from five patients’ sputa, one patient’s bedsore, and nasal swabs of ten patients and three nurses in ward I; five patients’ sputa, two patient’s urine, nasal swabs of eight patients and three nursing staff members including one nurse and two assistant nurses in ward II; and nasal swabs of one doctor and one nurse in charge of outpatients. Carriage rates of MRSA were 31% for inpatients and 9% for medical staff members. The isolates were tested for chromosomal DNA typing by using a contour-clamped homogeneous electric field system (CHEF Mapper: BioRad Laboratories, Hercules, Calif., USA), enterotoxin serotyping (SET-RPLA: Denka Seiken Co., Tokyo), toxic shock syndrome toxin-1 (TSST-1) production (TST-RPLA: Denka Seiken), and coagulase serotyping (Denka Seiken). Twenty-two different PFGE patterns of SmaI DNA digests were detected (Fig. 1). A band-based cluster analysis (Molecular Analyst: Bio-Rad), in which PFGE-band similarity exceeding 70% was used as the criterion of cluster formation, revealed 7 cluster patterns: A, G, H, C, I, E, and J (Fig. 2A). The frequency distribution of MRSA of these different PFGE patterns is shown in Fig. 2B. The most frequent pattern (A11) and the second-most frequent one (A1) represented 29% and 19% of the total isolates, respectively. Distribution of MRSA isolates in the wards is shown in Table 1. The isolates belonging to PFGE patterns A11 and A1 were the most