By David Beasley

ATLANTA (Reuters) - A Georgia college student was in critical condition on Thursday suffering with a rare, flesh-eating bacterial infection following a zip line accident last week.

Aimee Copeland, 24, was kayaking and zip-lining along the Little Tallapoosa River near Carrollton, Georgia, on May 1 when the line broke and she suffered a cut to her calf, her father, Andy Copeland, wrote in a Facebook posting.

Emergency room doctors closed the wound with 22 staples and released the woman, a graduate student at West Georgia University, her father wrote.

The next day, Copeland complained of severe pain and returned to the emergency room where she was given a prescription pain killer. The pain continued and the following day she went to a doctor who gave her a prescription for antibiotics. The doctor also ordered a magnetic resonance imaging test which was negative, her father said.

Last Friday, Copeland was pale and weak and went to a hospital where doctors diagnosed her with necrotizing fasciitis, a rare flesh-eating bacterial infection.

She was transferred to a burn center in Augusta where doctors amputated most of one leg, Andy Copeland wrote, describing his daughter's condition as "without a doubt the most horrific situation that a parent can possibly imagine."

Necrotizing fasciitis is often initially overlooked by doctors because it invades tissue deep inside the wound while the outer wound appears to be healing normally, Dr. William Schaffner of the Vanderbilt University Medical School told Reuters.

"This often is a very subtle infection initially," he said. "These bacteria lodge in the deeper layers of the wound. The organism is deep in the tissues and that's where it's causing its mischief."

On Thursday, Copeland was still listed in critical condition, said Barclay Bishop, spokeswoman for Doctors Hospital in Augusta.

"Aimee is awake, understands everything and is nodding her head to questions!" a posting on her university blog said Thursday. "Aimee is still on her life support, and we are waiting to hear more about how she is doing today."

(Editing By Tom Brown and Bill Trott)