I have recently taken care of a person with necrotizing fasciitis. I didn't know at the time what I was dealing with, and I am concerned about how careful I was. Just how contagious is necrotizing fasciitis?

P.P.

Necrotizing fasciitis is a severe infection of the skin and deeper tissues. It has received a lot of press in recent years and has been termed the "flesh-eating" infection. There are occasionally rumors, usually false, of various causes of this infection, including most recently, a false report regarding imported bananas.

Necrotizing fasciitis may start like any simple skin infection, with redness and mild pain. We usually call this form of simple skin infection, the kind that surrounds minor cuts, "cellulitis." In typical cellulitis, the infection progresses slowly and does not destroy the tissue. The more serious cases may require antibiotics, but there is little risk of death or loss of limb.

Necrotizing fasciitis, by contrast, spreads rapidly, involving large areas of skin and underlying tissue. Patients typically have severe pain, out of proportion to the appearance of the skin. There is extensive necrosis (cellular death) of the tissues. The bacteria often enter the bloodstream, causing signs of severe infection, shock and, without treatment, eventual death. Surgery is required to remove the dead, infected tissue for any reasonable chance of recovery.

Streptococcus pyogenes, or "strep," is the most common cause of this infection. (Sometimes, multiple bacteria can cause a very similar infection. This is common in groin and rectal-area infections.) In streptococcal disease, the legs are the most common sites of infection. Apparently, strep enters the deep layers of the skin through minor cuts or lacerations. The bacterium can also enter through a surgical incision. Some experts theorize that, at least in some cases, strep enters the bloodstream from the throat and then lodges in the skin. Once in the skin, the strep evades the normal defenses of the immune system and sets up the serious infection.

Blood-vessel disease and diabetes mellitus are risk factors for some forms of the infection, but they are not necessary factors in the development of streptococcal necrotizing fasciitis. Many patients were quite healthy before they developed the condition. One of the most important factors in determining whether a streptococcal skin infection turns into necrotizing fasciitis is the virulence (strength) of the strain of strep. Certain strains are much more likely to cause a serious infection.

If you were taking care of someone with necrotizing fasciitis, it would be important to know whether the person's disease was due to strep or if it was a mixed infection. If it was due to strep, then I hope you used standard precautions in caring for someone with an open wound. You should have worn gloves and washed your hands after touching the person. However, even if you did come in contact with a virulent strain of strep, you are not at that much risk. Most people who become colonized with these "hot" strains do not develop any serious disease. You may develop a minor infection such as strep throat or cellulitis, but necrotizing fasciitis developing in health-care workers caring for patients is rather uncommon.