Say what? 'Flesh-eating bacteria' explained

It sounds like something out of a horror film - a micro-organism that enters through an open wound and begins to consume your body from the inside out.

Unfortunately flesh-eating bacteria, or necrotizing fasciitis, isn't fiction. Aimee Copeland, a 24-year-old graduate student from Georgia, is fighting for her life in an Augusta hospital after contracting one type known as aeromonas hydrophila during a zip line adventure.

Aeromonas hydrophila is found in most, if not all, freshwater or brackish water environments (water that contains salt but is not saltwater), according to the Food and Drug Administration's "Bad Bug Book."

It is sometimes swallowed by swimmers, causing stomach or intestinal problems such as vomiting and diarrhea. It can also be found in fish and shellfish. The severity of the gastrointestinal infection depends on your immune system's ability to fight it off, according to the Mayo Clinic.

Aeromonas hydrophila can also enter the body through an open wound, as happened in the Copeland case. When that occurs the flesh-eating bacteria quickly reproduces, giving off toxins that destroy skin and soft tissue. Such bacteria is adept at hiding from the body's immune system, according to the National Necrotizing Fasciitis Foundation.

If necrotizing fasciitis is detected early, only skin or fat may need to be removed. But if the infection is detected later, amputation may be necessary to stop the spread of the bacteria.

Dr. William Schaffner, president of the National Foundation for Infectious Diseases, says when Aeromonas hydrophila enters through an open wound, early diagnosis is difficult. The bacteria does its damage deep in the tissue and doesn't manifest itself on the skin's surface.

Patients should pay attention to any pain coming from a closed wound, as well as redness or drainage, he told CNN.

The frequency of Aeromonas hydrophilia infections is unknown, the FDA notes, because researchers only recently began trying to collect numbers.

The Centers for Disease Control and Prevention estimates that each year there are about 10,000 U.S. cases of group A streptococcus, a collection of bacteria that includes necrotizing fasciitis. Approximately 20% of the cases of necrotizing fasciitis are fatal, according to the CDC.