Objective. More than 70% of the community-acquired (CA) staphylococcal infections treated at Texas Children's Hospital are caused by methicillin-resistant Staphylococcus aureus (MRSA). Since September 2002, an increase in the number of severely ill patients with S aureus infections has occurred. This study provides a clinical description of severely ill adolescent patients and an analysis of their isolates using molecular methods.

Methods. We identified adolescent patients meeting criteria for severe sepsis requiring admission to the PICU. Patient records were reviewed, and isolates were obtained for susceptibility testing and DNA extraction. Isolates were tested for the presence of virulence genes (cna, tst, lukS-PV, and lukF-PV) and enterotoxin genes (sea, seb, sec, sed, seh, and sej) by polymerase chain reaction. Genomic fingerprints were determined by repetitive-element polymorphism polymerase chain reaction and pulse-field gel electrophoresis. SCCmec cassette type was determined.

Results. Fourteen adolescents with severe CA S aureus infections were identified between August 2002 and January 2004. All were admitted to the PICU with sepsis and coagulopathy. Twelve patients had CA-MRSA infections; 2 had CA methicillin-susceptible Staphylococcus aureus (MSSA) infections. The mean age was 12.9 years (range: 10-15 years). Thirteen patients had pulmonary involvement and/or bone and joint infection; 10 patients had ≥2 bones or joints infected (range: 2-10); 4 patients developed vascular complications (deep venous thrombosis); and 3 patients died. All isolates were identical or closely related to the previously reported predominant clone in Houston, Texas (multilocus sequence type 8, USA300), and carried lukS-PV and lukF-PV genes as well as the SCCmec type IVa cassette (12 MRSA isolates) but did not contain cna or tst. Only 1 strain carried enterotoxin genes (sed and sej).

Conclusions. Severe staphylococcal infections in previously healthy adolescents without predisposing risk factors have presented more frequently at Texas Children's Hospital since September 2002. CA MRSA and clonally related CA MSSA characterized as USA300 and sequence type 8 have been isolated from these patients.

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