Typically, the infection enters the body through a break in the skin such as a cut or burn. Risk factors include poor immune function such as from diabetes or cancer, obesity, alcoholism, intravenous drug use, and peripheral artery disease. It is not typically spread between people. The disease is classified into four types, depending on the infecting organism. Between 55 and 80% of cases involve more than one type of bacteria. Methicillin-resistant "Staphylococcus aureus" (MRSA) is involved in up to a third of cases. Medical imaging is often helpful to confirm the diagnosis.