Risk factors and molecular analysis of Panton-Valentine leukocidin-positive methicillin-susceptible Staphylococcus aureus colonization and infection in children.

BACKGROUND AND PURPOSE Limited information is available regarding the role Panton-Valentine leukocidin (PVL) plays in methicillin-susceptible Staphylococcus aureus (MSSA). In this study, we compared the frequency of the PVL gene between MSSA strains isolated from patients with MSSA infections and MSSA strains isolated from patients with evidence of MSSA nasal colonization. We also explored the role that the PVL toxin plays in the ability of MSSA to cause disease as well as the phylogenetic relationship between these S aureus strains. METHODS The presence of MSSA strains was screened among children aged <18 years during routine health maintenance visits and among children aged <7 years at daycare centers or kindergartens during the 2003 to 2008 period. At the same time, clinical MSSA isolates were recovered from patients with various types of bacterial infections. Polymerase chain reaction was applied to detect the presence of the PVL and SEB genes in these strains. The strains were also subjected to pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) studies. Clinical features were compared between patients with PVL-positive and those with PVL-negative isolates. RESULTS A total of 495 colonizing MSSA and 71 clinical MSSA isolates were used. The prevalence of PVL-positive S aureus was significantly higher among clinical isolates than among colonizing isolates (14/71, 19.7%; 5/495, 1.0%; p < 0.05). In addition, we found that patients with PVL-positive MSSA infections had a significantly longer duration of fever and tended to have higher C-reactive protein levels than patients with PVL-negative MSSA infections. MLST typing of the 19 PVL-positive MSSA isolates revealed ST59, a strain that is similar to the MLST type of community-associated methicillin-resistant Staphylococcus aureus found in Taiwan. The PFGE typing of PVL-positive/ST59 MSSA isolates revealed multiple pulsotypes. CONCLUSION The prevalence of the PVL gene was significantly higher among clinical strains of MSSA (19.7%) than among colonizing strains (1.0%). In addition, patients infected with PVL-positive MSSA strains had fever for a significantly longer duration and tended to have higher C-reactive protein levels than patients with PVL-negative MSSA infections. Our findings imply that PVL may play an important role in the pathogenesis of S aureus infection.