Necrotizing soft-tissue infections can be divided into two types: type I (polymicrobial) and type II (monomicrobial). Approximately 70% of infections are type I; type II infections usually involve group A streptococci. The incidence of necrotizing fasciitis is difficult to determine, since the classification and coding of these infections is poor; a conservative estimate is 1500 severe cases per year in the United States.
Risk factors for the development of these infections include diabetes, renal failure, liver failure, advanced age, behavior risks (e.g., intravenous drug abuse), and obesity. However, more than 20% of cases have no known risk factors. The patient in the case had recently given birth by means of a surgical procedure, and the wound could have been contaminated by organisms from the patient's skin or from a health care worker.
New England Journal of Medicine - Vol. 361, No. 17, October 22, 2009