ROCKVILLE, Md., Mar 13, 2001 (United Press International via COMTEX) -- More Americans are eating tuna, especially tuna burgers, but as the popularity of tuna grows so does the risk of histamine poisoning, according to a new study by CDC epidemiologists.

Histamine poisoning is usually nonfatal but does cause vomiting, diarrhea, cramping, headaches and facial flushing --symptoms unpleasant enough to send most victims to hospital emergency rooms, said Dr. Karen Becker, lead author of the study, which appears in tomorrow's Journal of the American Medical Association.

People who have a case of histamine poisoning usually, "just think they have had an allergic reaction to fish," Becker said. She said that more cases of histamine poisoning, also called scombroid poisoning, are being seen because more Americans are eating fish more often. Case in point: last fall the winning burger recipe in Sutter Home Wineries' "Build a Better Burger" contest was a tuna burger with "Wowee Maui Salsa."

Becker studied histamine poisoning in North Carolina. She said that from 1994 to 1997 there were only four reported cases of histamine poisoning in the state but from July 1998 to February 1999 a total of 22 cases were reported, "a significant increase."

Becker, a CDC researcher in Rockville, Md., said that -- unlike bacterial contamination of meat and poultry -- histamine poisoning cannot be avoided by careful preparation and cooking.

Walter Staruszkiewicz, the histamine expert at the Food and Drug Administration's Washington, D.C. Seafood Laboratory, explained, "you can't cook histamine poisoning out of fish. Once it is there, it stays." Staruszkiewicz was not involved in Becker's study.

Histamine is created when histidine C5H9N3, a chemical compound found in most fish, breaks down as the fish dies. The only way to stop the process -- and prevent histamine from contaminating the fish -- is to freeze the fish within 6 hours of capture, said Staruszkiewicz.

Although histamine contamination has been detected in several varieties of saltwater fish, tuna are especially susceptible because they "heat up as they die, the internal temperature can increase by as much as 10 degrees Celsius, which increases the risk for histamine formation," Staruszkiewicz said. Moreover, two of the most popular tuna varieties, yellow fin and skip jack, are caught in warm waters, which again increases the risk, he said. The risk is slightly lower with albacore, which is fished in colder waters.

The FDA considers a "safe" level of histamine to be no more than 50 ppm or parts per million. In the study by Becker the tuna that caused poisonings had from 213 to 3245 ppm, she said. "Eighteen people ate tuna burgers served in restaurants in North Carolina, two people ate tuna salad and two ate tuna filets," she says. Especially disturbing was the finding that "twenty-one cases involved tuna served at a very upscale, fancy restaurant."

Staruszkiewicz said he isn't surprised that contaminated fish end up on the menu of an upscale restaurant. He said that identifying histamine-contaminated fish is very difficult because the "fish don't smell particularly bad and they don't look very different from non-contaminated fish," he said. He said the FDA has three experts who can sniff out histamine but said that he doesn't have the ability to pick up by odor alone. For those who get a chance to examine a "fresh catch before it is butchered or shipped across country" he said there are a few visual signs of contamination: brown instead of red inside the gills and cloudy versus clear eyes. But once the fish has been butchered or cleaned, it is virtually impossible to spot contamination, he said.

Becker said another test involves, "poking the fish to see if it bounces back or the indentation remains. If it doesn't bounce back, don't buy the fish."

Staruszkiewicz said the FDA has also received reports of histamine poisoning associated with canned fish products, but those reports have decreased as the large canning operations have perfected the use of refrigeration and freezing on commercial fishing vessels.

(Reported by Peggy Peck in Cleveland, Ohio.)

By UPI Science News

Copyright 2001 by United Press International.

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