Emergence of a predominant clone of community-acquired Staphylococcus aureus among children in Houston, Texas.

Background: Community-acquired (CA), methicillin-resistant Staphylococcus aureus (MRSA) infections among children are increasing in the United States. At Texas Children's Hospital (TCH), surveillance has been in place since August 2001. The objectives of this study were to describe the distribution of CA S. aureus among patients at TCH and to study genomic relationships of isolates collected between August 2001 and July 2003.

Methods: Genomic relationships were determined with repetitive element-polymerase chain reaction (PCR). Multilocus sequence typing was performed for selected strains representing major clones. Molecular characterization of CA-MRSA was performed with PCR, including staphylococcal cassette chromosome (SCCmec), pvl (lukS-PV plus lukF-PV), hla, hlb and selected microbial surface components recognizing adhesive matrix molecule genes, ie, cna, clfA, fnbA and fnbB.

Results: A 62% increase was observed in CA S. aureus infections from year 1 (2001-2002) to year 2 (2002-2003), whereas the annual number of hospital admissions was unchanged. CA methicillin-sensitive S. aureus isolates were more likely to be associated with invasive infections than were CA-MRSA isolates (P < 0.01). TCH clone A, sequence type (ST) 8, was responsible for approximately 94% of all CA-MRSA isolated from children in the greater Houston area. Clone A differed from clones B (ST30) and C (ST1) by lacking the cna gene while carrying the fnbB gene.

Conclusions: One CA-MRSA clone, TCH clone A, has become the predominant cause of CA S. aureus infections among children in the Houston area. It causes a wide spectrum of diseases, including complicated pneumonia.