A severe, life-threatening infection caused by bacteria that attack the soft tissue beneath the top layers of skin, including the fibrous tissue that covers the muscles. Necrotizing fasciitis group A is usually caused by group A Streptococcus and other bacteria that enter the body via an infection or minor cut or lesion on the surface of the skin. It occurs most commonly on the arms and legs, but may also affect the perineum (the tissue between the external genitalia and the anus). The infection is sometimes a complication of surgery. People with diabetes mellitus may be particularly susceptible to necrotizing fasciitis group A, but it also affects people who are otherwise in good health.