Epidemiology of necrotizing infection caused by Staphylococcus aureus and Streptococcus pyogenes at an Iowa hospital

The present study was performed to characterize the epidemiology of necrotizing soft tissue infection caused by Streptococcus pyogenes (n=14) and Staphylococcus aureus (n=14) isolates collected at the University of Iowa Hospitals and Clinics. An additional 9 S. pyogenes isolates were collected from patients being treated for mild respiratory infections and served as a comparison sample in the analysis. Patient data corresponding to the isolates (n=37) were also collected in order to identify risk factors or comorbid conditions possibly correlated with necrotizing fasciitis (NF). The prevalence of methicillin-resistant S. aureus among the study isolates was 35.7% (5/14), and the prevalence of the Panton-Valentine leukocidin (PVL) gene was 57% (8/14). The S. pyogenes NF (wound) isolates (n=14) belonged to 10 different emm types, none of which appeared to be associated with more severe disease when compared to the milder infection (throat) samples (n=9). Comorbid conditions such as diabetes and cardiovascular disease were significantly associated with NF. The results indicate that there may be a high prevalence of the PVL virulence factor in NF infections and that spa type t008 may be responsible for the increasing incidence of S. aureus NF infections in Iowa.