Doctors removing a young man's appendix were surprised when the real cause of his pain wriggled into view - a 2-inch-long red worm he had eaten with his homemade sushi.

When the patient came to the hospital in pain, doctors assumed he had appendicitis. But his appendix looked normal during sugery, and as they were about to sew him up, the worm slithered out of his abdominal cavity and onto the surgical drapes.After he awoke, the man remembered eating raw fish the night before at a friend's home in New York City.

"There is a clear danger involved in eating raw fish. This underscores that danger," said Dr. Murray Wittner, a parasitologist at Albert Einstein College of Medicine who was sent the worm by the surgeons.

While worms have been a long-recognized hazard of eating raw fish, experts say most cases of worm infection occur when people prepare it at home. At restaurants, sharp-eyed sushi chefs are probably adept at keeping wormy fish from reaching customers.

In the latest case, described in the New England Journal of Medicine, doctors identified the culprit as a larval nematode known as eustrongylides. The adult form of this creature is a parasite of fish-eating birds, while the larvae are found in the flesh of fish that live in brackish and fresh water.

In an editorial in the journal, Dr. Peter M. Schantz of the U.S. Centers for Disease Control noted that only four previous cases of human infection with this nematode have been reported. All were fishermen who swallowed bait minnows whole - "a practice not likely to be widely imitated."

The victim in the latest case recovered uneventfully after the doctors plucked the worm from his incision.

The worms most commonly acquired from raw seafood are larvae of the family Anisakidae. Twenty-five to 50 U.S. cases have been documented, but experts believe most cases are not recognized or reported.

Often the worms pass harmlessly through the digestive system or are coughed up a few hours after the meal. Doctors have even described a condition known as "tingling throat syndrome," which occurs when the worms get stuck in the back of the throat.

Sometimes, however, the worms burrow into the wall of the stomach or the intestines. They must be removed with a tube pushed down the victim's throat.