A pesky toxin found in barracuda and other tropical fish has been sickening more people than previously thought, according to a study published Monday by the American Journal of Tropical Medicine and Hygiene.

Ciguatera can't be cooked or frozen out of infected fish. You can't smell it or see it with the naked eye, either. And while some who eat infected fish don't develop any symptoms, many people do get sick with symptoms that can last for weeks and even months, researchers said. Side effects range from severe vomiting and diarrhea to tingling in the mouth. Some people even experience "temperature reversal," in which touching hot things feels cold and vice-versa, the study notes.

The small fish that nibble on coral reef algae, which contains the ciguatera toxin,  then get eaten by larger fish, such as barracudas. "It gets concentrated as it moves up. That's why eating the big fish is the most dangerous," said lead author Elizabeth Radke, an epidemiologist  at the University of Florida's Emerging Pathogens Institute.

Hispanics are among the most at risk of getting food poisoning from the toxin, and researchers write that it might be because they are more likely to eat barracuda than other demographic groups. Other fish known to sicken people include grouper, amberjack, hogfish, and to a lesser extent, snapper, mackerel and mahi mahi.

"We definitely caution against eating barracuda," Radke said.

While Radke didn't say people should swear off other tropical reef fish, she added: "It's important to know that if you eat one of these large, carnivorous fish from tropical or subtropical areas, including South Florida, there is a risk. And if you get sick after eating them, you should see a doctor and let them know you've eaten saltwater fish."

Most of the fish are found in the tropical waters of southern Florida and the Caribbean, although infected fish have sickened people as far north as North Carolina. "It's possible to see things move further north over time, with warmer sea water temperatures, but for the most part we're talking about fish caught in tropical or subtropical areas," Radke said.

Researchers combed through 291 Florida cases from 2000 to 2011 and also surveyed by e-mail more than 5,000 licensed recreational saltwater fishers. They estimated that the dangerous and rare toxin results in 5.6 cases per 100,000 people, which is much higher than the previous estimate of 0.2 cases per 100,000 people. In Miami-Dade County alone, the study estimate — 28 cases per 100,000 people — is 28 times higher than state health records.

Radke said poisonings may be underreported for a number of reasons; some who are sickened may not go to the doctor, or doctors might miss the diagnosis (there is no lab test that can show someone is infected), or doctors may not know that they have to report the cases to the state health agency.

While not finding evidence that cases are on the rise, the data provide a baseline for future research to track the toxin, and whether the problem could increase, with fish carrying the toxin migrating to more northern waters, Radke said.

The Florida State Health Department, whose researchers also worked on the study, plans to boost awareness around ciguatera, according to a release. Radke said the higher poisoning rate among Hispanics presents an opportunity for targeted public health outreach.

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