Regional outbreak of community-associated methicillin-resistant Staphylococcus aureus ST834 in Japanese children.

BACKGROUND: Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has recently become a challenging problem worldwide and in Japan. We experienced 10 pediatric patients infected with CA-MRSA and hospitalized from 2011 to 2014 in a tertiary care hospital in Saitama, Japan, and assessed the characteristic of the strains using a whole genome sequencing (WGS)-based approach. METHODS: CA-MRSA strains isolated from infected patients who required hospitalization for treatment were evaluated in this study. Antimicrobial susceptibility tests, molecular typing by PCR and pulse-field gel electrophoresis (PFGE) were performed to characterize MRSA strains. WGS was performed for detailed genetic analysis. RESULTS: A total of 582 MRSA strains (35.2%) were identified among 1625 S. aureus strains collected during the study period. Ten MRSA strains (1.7%) were defined as CA-MRSA clinically, and all were isolated from pediatric patients. All strains mainly caused purulent lymphadenitis, were susceptible to fluoroquinolone and tetracycline, exhibited sequence type (ST) 834 or its single-locus variants and contained staphylococcal cassette chromosome mec (SCCmec) type IVc. Phylogenic analysis by PFGE and WGS revealed close relatedness of all strains, with the number of single nucleotide polymorphisms ranging from 35 to 119 by WGS. Out of the ten strains, nine possessed the genomic island SaPISaitama2 containing tst, sec and sel genes. SaPISaitama2 comprises a mosaic of genomic islands SaPIm4 and SaPIm1 harbored by a hospital-associated MRSA strain Mu50. CONCLUSIONS: This study describes a regional outbreak of ST834-related CA-MRSA in children with a unique pathogenicity island in Japan. Pediatric patient tropism of this clone could be enhanced by susceptibility to fluoroquinolones and tetracyclines, which cannot be prescribed to children.

Characteristics of Clostridium difficile colonization in Japanese children.

In children, asymptomatic colonization with Clostridium difficile is well known, but its prevalence in Japanese children is not fully understood. The objective of this study was to determine the colonization rate of C. difficile and to identify the risk factors for C. difficile colonization in Japanese children. Single fecal samples were prospectively collected from children hospitalized in Saitama City Hospital between August 1, 2012, and March 31, 2013. Samples were obtained from neonates, at 4-14 days after birth, and from non-neonatal children, principally within 2 days after admission, to determine community-associated colonization. The fecal samples were cultured for C. difficile, and isolated strains were tested for production of Clostridial toxins A/B. In 95 neonates, the colonization rate of C. difficile was 0%. The 251 non-neonatal children were divided into two subgroups, depending on the presence or absence of underlying disease. In the subgroup without underlying disease, the colonization rates of C. difficile and toxin-positive C. difficile were 21.6% and 9.0%, respectively, while in the subgroup with underlying disease, values were 30.8% and 23.1%, respectively. The proportion of toxin-positive C. difficile in all of the culture-isolated strains from the latter subgroup (75.0%) was statistically higher than that from the former subgroup (41.9%) (P = 0.049). Multivariate logistic regression analysis indicated an association of tube feeding with significantly higher colonization rates of C. difficile (Odds Ratio(OR) = 24.28; 95% confidence interval(CI)[4.70-125.34]; P < 0.001) and toxin-positive C. difficile (OR = 8.29; 95%CI[1.87-36.84]; P = 0.005). Further evaluations are recommended to assess the epidemiology and the role of C. difficile in Japanese children.