Tuna burgers may be a health hazard, according to a government study that traced food-poisoning outbreaks in North Carolina to the relatively new menu item. Made with ground tuna, the burgers may be especially susceptible to contamination with histamine, a chemical produced by bacteria. The grinding process can mix bacteria into the fish or increase the tuna's temperature through friction, the researchers reported in the Journal of the American Medical Assn. Contaminated fish may appear and smell normal, and cooking does not destroy the toxicity. Symptoms may include a tingling sensation in the mouth, an upper-body rash, vomiting and heart palpitations.