Genotypes, intrafamilial transmission, and virulence potential of nasal methicillin-resistant Staphylococcus aureus from children in the community

Pediatric outpatients and healthy children in the community were examined for nasal methicillin-resistant Staphylococcus aureus (MRSA) in Japan. MRSA isolation frequencies were 0.7% (3/426) and 3.7% (5/136), respectively, in pediatric outpatients and healthy children in the community (overall frequency, 1.4%). The frequency of MRSA isolation was higher in children 5–9 years of age compared with the other age groups. All eight MRSA strains isolated were Panton-Valentine leukocidin-negative. Of these, three with the genotype multilocus sequence type (ST) 8/ spa 606/SCC mec IV (2 cases) and ST88/ spa 999/SCC mec IV/exfoliative toxin A gene ( eta ) were identical or similar to MRSA from bullous impetigo, determined by pulsed-field gel electrophoresis. One strain with ST764 (ST5 variant)/ spa 2/SCC mec II/staphylococcal enterotoxin B gene seb2 ( seb variant) was similar to MRSA from bacteremia, and one with ST5/ spa 2/SCC mec II was the Pandemic New York/Japan clone. The remaining three strains, with ST22/ spa 998/SCC mec I, ST380/ spa 799/SCC mec IV, and ST857/ spa 416/SCC mec II, have not been identified. All MRSA strains were resistant to one or more non-β-lactam antibiotics, and the ST5 and ST764 strains were multidrugresistant. Family analysis demonstrated parent-to-child transmission (for ST8 and ST764), as well as acquisition from outside the family (for ST8 and ST380). The data suggest that young school-age children have a higher carriage rate of nasal MRSA than children of other ages, and that not only community-acquired MRSA strains but also MRSA strains with characteristics of hospital-acquired MRSA are spreading in the community.