Molecular epidemiology and pathogenicity analysis of community-acquired MRSA in Japanese children with a severe or recurrent infection.

Reports of severe infections caused by Panton-Valentine leukocidin (PVL)-positive community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are increasing. Pediatric infections caused by CA-MRSA, including in children without known risk factors, are on the rise worldwide. In recent years, PVL-producing USA300-related clones and ST22-PT clones producing both PVL and toxic shock syndrome toxin-1 (TSST-1) have been identified, which suggests an emerging threat. We treated 10 pediatric patients with severe or recurrent MRSA infections between 2021 and 2024. These included four cases of recurrent subcutaneous abscesses, two cases of necrotizing pneumonia, and one case each of bacteremia, suppurative osteomyelitis, cellulitis, and infective endocarditis. Four patients had underlying medical conditions. Molecular analysis revealed that all of the isolates carried SCCmec type IV, 50% were PVL-positive, and 30% produced TSST-1. Multilocus sequence typing showed that 60% of isolates belonged to sequence type (ST) 8 clones suspected to be USA300-related variants. Furthermore, one isolate belonged to the ST22-PT clone. These findings revealed that CA-MRSA accounts for the majority of MRSA infections even in pediatric patients, with severe cases caused by PVL or TSST-1 positive strains. CA-MRSA has also spread within healthcare settings and could pose a significant risk to pediatric patients with underlying conditions. Furthermore, the results suggest that severe infections caused by USA300-related clone and ST22-PT could increase in the future. Ongoing molecular surveillance is essential to guide effective treatment and infection-control strategies.