Question: What is (are) Necrotizing fasciitis ?
Answer: Necrotizing fasciitis is a serious infection of the skin, subcutaneous tissue (tissue just beneath the skin) and fascia. The infection can arise suddenly and spread quickly. Necrotizing fasciitis can be caused by several different types of bacteria. Early signs include flu-like symptoms and redness and pain around the infection site. If the infection is not treated promptly, it can lead to multiple organ failure and death. As a result, prompt diagnosis and treatment is essential. Treatment typically includes intravenous antibiotics and surgery to remove infected and dead tissue.
Source: GARD

Question: What causes Necrotizing fasciitis ?
Answer: What causes necrotizing fasciitis? Bacteria that can cause necrotizing fasciitis (NF) include the following: Klebsiella, Clostridium, and Escherichia coli; group A Streptococcus is the most common cause. Anyone can develop NF. Approximately 50% of necrotizing fasciitis cases caused by streptococcal bacteria occur in young and otherwise healthy individuals. Although necrotizing fasciitis most frequently develops after trauma that causes a break in the skin, it can also develop after minor trauma that occurs without a break in the skin. NF can occur as a complication of a surgical procedure; it can also occur at the site of a relatively minor injury such as an insect bite or an injection. In addition, underlying illnesses which weaken the immune system may increase the risk that a person will develop NF. Studies have even suggested a possible relationship between the use of nonsteroidal anti-inflammatory medications (NSAIDs) during varicella infections and the development of necrotizing fasciitis.
Source: GARD