Recurrent familial furunculosis associated with Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus sublineage of the USA300 clone in Tokyo.

We report a familial case of recurrent furunculosis caused by Panton-Valentine leukocidin (PVL)-positive community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Tokyo. The index case, a 34-year-old female, and her family members (her husband and their 8-month-old son) were also affected, and all recovered after treatment with oral clindamycin, intranasal mupirocin, and hygiene interventions. Whole-genome sequencing revealed that five isolates from skin and nasal swabs belonged to ST8-IVa-t304, carrying ACME type I and PVL genes. All isolates were resistant to levofloxacin but susceptible to other anti-MRSA agents. Genomic analysis showed the absence of the SaPI5 island and the sek/seq genes. Based on phylogenetic analysis, we concluded that these strains represent a unique USA300-like sublineage that diverged from the closest USA300-NAE lineage. The USA300 clone has emerged globally as a dominant CA-MRSA lineage responsible for severe skin and soft tissue infections. In Japan, PVL-positive USA300-related clones have been increasingly identified in recent years, indicating ongoing diversification of community-associated MRSA lineages. This case illustrates the growing presence of USA300-related clones in Japan and the need for genomic surveillance and early intervention to prevent further spread in community settings.