Case Study: Outbreak Response

EHA consulted on a small outbreak of food poisoning which, at first look, appeared to be straightforward. Restaurant patrons had ordered and consumed what they believed to be Rockfish, then presented gastrointestinal as well as neurological symptoms. Laboratory analysis determined the illnesses to be Ciguatera toxin poisoning.

Ciguatera is a foodborne illness caused by eating carnivorous predatory species of fish which have fed on herbivorous species of reef fish, the flesh of which is contaminated with varietal toxins produced by dinoflagellates living in tropical and subtropical waters. Gambierdiscus toxicus is the primary dinoflagellate responsible for the production of toxins which include ciguatoxin, maitotoxin, scaritoxin and palytoxin, any of which may lead to ciguatera. The toxins are produced during harmful algae blooms known as “red tides”. Dinoflagellates adhere to coral, algae and seaweed and are eaten by herbivorous fish, which, in turn, are eaten by larger carnivorous fish. In this manner, the toxins move up the food chain and threaten human food safety. Notably, ciguatera-causing toxins are heat-resistant and, therefore, cannot be rendered harmless or neutralized by conventional cooking of the fish that carry them.

Predator species most likely to carry these toxins live and are fished in tropical and subtropical waters and include barracuda, snapper, moray eel, parrotfish, grouper, triggerfish and amberjack.

Based on the aforementioned facts, local officials were stymied in that the affected patrons stated that they had ordered and (they thought) consumed Rockfish, an expensive fish which doesn’t fit the profile of the previously described carnivorous, predatory reef fish.

EHA experts found it curious that Rockfish was a menu offering in a mid-Atlantic restaurant not far from the Chesapeake Bay, considering the fact that Rockfish is an overfished, controlled species most notably sourced from the west coast of the United States and Canada and, thus, expensive in relation to the other offerings at the involved restaurant. Rockfish can be legally marketed or identified as snapper or Pacific Snapper, but only in the state where it was harvested.

The combination of disconnects identified during this outbreak led EHA experts to dig deeper and widen their investigation. EHA subsequently uncovered the fact that the restaurant had indeed offered Rockfish on its menu, but had run out that day and substituted Grouper, a species which perfectly fits the risk profile for carrying ciguatoxins.

Healthcare professionals unfamiliar with ciguatoxins have at times misinterpreted the neurological symptoms occurring from ciguatera, leading to misdiagnoses such as multiple sclerosis. Base on this and other factors, EHA intervened to assist affected persons in getting proper medical attention and post-event guidance.