Biological Contamination

As you learned, a foodborne intoxication occurs when a person eats food containing toxins. The toxin may have been produced by pathogens found on the food or may be the result of a chemical contamination. The toxin could also come from a plant or animal that was eaten. Toxins in seafood, plants, and mushrooms are responsible for many cases of foodborne illness in the United States each year. Most of these biological toxins occur naturally and are not caused by the presence of microorganisms. Some occur in animals as a result of their diet.

Seafood Toxins

The ciguatera toxin occurs in certain predatory tropical reef fish, such as amberjack, barracuda, grouper, and snapper. Ciguatera accumulates in the tissue of these large, predatory fish after they eat smaller fish that have fed upon certain species of toxic algae. When a person eats fish containing this toxin, an illness may result, requiring weeks or months of recovery. Symptoms of ciguatera poisoning include vomiting, severe itching, nausea, dizziness, hot and cold flashes, temporary blindness, and, sometimes, hallucinations. Because the ciguatera toxin cannot be smelled or tasted and it is not destroyed by cooking, it is very important to purchase predatory tropical reef fish only from approved suppliers.

Shellfish may contain toxins that occur because of the algae upon which they feed. Illnesses caused by shellfish poisoning vary and are specific to the type of toxin consumed. Paralytic shellfish poisoning (PSP), the most serious type, may lead to respiratory failure and even death if respiratory support is not provided. PSP is generally associated with mussels, clams, cockles, and scallops. Since cooking may not destroy shellfish toxins, it is important to purchase shellfish from approved suppliers who can certify that the shellfish have been harvested from safe waters.

Scombroid poisoning is one of the more common forms of illness caused by fish toxins in the United States. It occurs when scombroid species of fish—such as tuna, mackerel, bluefish, skipjack, swordfish, and bonito - are time-temperature abused. Under these conditions, bacteria associated with the fish produce the toxin histamine. This odorless, tasteless chemical causes scombroid intoxication when consumed. Symptoms of the illness include flushing and sweating, a burning, peppery taste in the mouth, dizziness, nausea, and headache. Sometimes a facial rash, hives, edema, diarrhea, and abdominal cramps will follow. Scombroid poisoning, also known as histamine poisoning, has been associated with other fish species as well, such as mahi-mahi, marlin, and sardines. Histamine is not destroyed by cooking or freezing. Since time-temperature abuse during the harvesting process may cause scombroid fish to become unsafe, it is important to purchase these fish from reputable suppliers who practice strict time-temperature controls.

Some fish toxins are systemic: that is, they occur as a natural part of the fish. An example of a potentially toxic fish is puffer fish, which contains tetrodotoxin in its liver, skin, and other organs. Consuming the toxin in this fish can produce rapid and violent death. Few cases of this type of poisoning have been reported in the United States. Cooking may not destroy systemic fish toxins. Puffer fish should be eaten only if they are handled and prepared by a trained and licensed chef.

The following general procedures should be practiced to guard against a seafood-specific foodborne illness.

Purchase fish from reputable suppliers who maintain strict time-temperature controls.

Refuse fish that has been thawed and refrozen.

Check temperature. The temperature of fresh fish must be 4l °F (5 °C) or lower upon arrival. However, this temperature standard will not prevent a scombroid poisoning if the fish has been temperature-abused during the harvesting process or prior to being received. This is why it is critical to purchase fish from reputable suppliers.

Thaw frozen fish at refrigerator temperatures of 4l °F (5 °C) or lower.

Remember that toxins are not living organisms, so cooking or freezing may not destroy them. Therefore, most of the preventive measures taken against biological toxins in seafood must be implemented when purchasing and receiving.

Plant Toxins

Plant toxins are another form of biological contamination. Most poisonings caused by plants result when toxic plants have been used in medicinal home remedies. Foodborne illnesses have occurred after people have consumed rhubarb leaves, jimsonweed, and the root of water hemlock. Some illnesses have occurred after animals have eaten toxic plants and people have consumed the byproducts of those animals. For example, people have become ill after consuming milk from cows that had eaten snakeroot. People have also become ill from consuming honey produced by bees that had gathered nectar from mountain laurel or rhododendrons.

Some plants may be toxic in their raw state but safe when properly cooked. For example, fava beans and red kidney beans may be unsafe if eaten when raw or undercooked. In general, toxic plant species and products prepared with them should be avoided. Only commercially processed honey and properly cooked beans should be used.

Mushroom Toxins

Foodborne-illness outbreaks associated with mushrooms are almost always caused by the consumption of wild mushrooms collected by amateur mushroom hunters. Most cases occur when toxic mushroom species are confused with edible species. The symptoms of intoxication vary depending upon the species consumed. Some mushroom toxins will destroy internal organs; others cause convulsions, hallucinations, and coma; still others produce nausea, vomiting, abdominal cramping, and diarrhea.

Cooking or freezing will not destroy the toxins produced by toxic wild mushrooms. Establishments should not use wild mushrooms or products made with them. All mushrooms should be purchased from approved suppliers.

Chemical Contaminants are responsible for many cases of foodborne illness. Contamination can come from a variety of substances normally found in restaurant and foodservice establishments. These include toxic metals, pesticides, and chemicals.

Toxic Metals

Utensils and equipment that contain toxic metals - such as lead, copper, brass, zinc, antimony, and cadmium - can cause a toxic metal poisoning.

If acidic food is stored in or prepared with this type of equipment, it can leach these metals from the item and become contaminated. For example, storing tomato sauce in a copper pot or lemonade in a pewter pitcher could lead to a foodborne illness. Only food-grade utensils and equipment should be used to prepare and store food.

Improperly installed carbonated-beverage dispensers can also create a hazard. If carbonated water is allowed to flow back into the copper supply lines, it could leach copper from the line and contaminate the beverage. Beverage-dispensing systems should be installed and maintained only by professionals who will ensure that a proper backflow-prevention device is installed.

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