Fishy Reaction
Nurses need to be alert to scombroid poisoning, a unique toxic reaction caused by eating certain seafood that requires a specific regimen of care

By Maureen G. Sullivan-Tevault, RN, CEN
March 28, 2005

This afternoon, you’re seeing your middle-age patient Stanley* on an emergency basis. He has symptoms of an allergic reaction — he’s covered with a bright red, itchy rash — though there are no visible wheals. You ask what he may have eaten recently, and Stanley says he just had lunch with his wife at a local seafood restaurant, ordering grilled mahi-mahi. But before he finished the meal, he felt flushed, and his heart was racing.

For several minutes, you’re stumped. Stanley has no allergy to anything that you’re aware of. In fact, he’s the least likely of your patients to have a food reaction: Stanley’s diet rarely strays from the straight and narrow — basically, as he once said, he’s a meat-and-potatoes man.

You ask Stanley about the mahi-mahi, and he replies that his wife talked him into trying the dolphin, “just for something different.” Different it was — the fish had an unpleasant, rather acrid taste. “Next time,” he says, “I’m getting the steak!”

That’s when you realize what ails him — scombroid poisoning — and you order the antihistamine medication standard for an allergic reaction.

The real culprit

But though treatment resembles what practitioners administer to counteract an allergy, scombroid poisoning (or histamine poisoning) is just that: a toxic reaction that can occur after eating certain inadequately preserved fish. Originally, it was associated with the suborder Scom­ broidea, which includes such fish as tuna, mackerel, and butterfly kingfish. Nowadays, however, nonscombroid fish like dolphin and amberjack are thought to be the major vectors.

According to the Centers for Disease Control and Prevention, scombroid poisoning is the leading food-borne disease in the United States that’s caused by a chemical agent. It accounts for about 5% of food-borne outbreaks reported each year, but since health care providers are not required to report these illnesses, the actual number of poisonings may be far higher.¹

Scombroid fish contains a chemical called histadine. Bacteria multiply in fish stored in a warm environment and convert histadine into scombrotoxin. The main component of scombrotoxin is histamine, which is the cause of symptoms associated with scombroid poisoning.² Cooking, smoking, curing, canning, or freezing the fish does not reduce histamine levels, even though the causative bacteria may have been destroyed.³

It’s important to note that the amount of histamine can vary with the type or size of the fish, so not everyone eating the same food may be affected by histamine poisoning.² Although there’s no test for this toxin that’s 100% reliable, many who’ve ingested the sus­ pect fish say it has a
distinctive peppery, bitter taste.⁴

That said, the diagnosis is usually made clinically based on presenting symptoms, and treatment consists of both H1 and H2 histamine blockers, in addition to supportive care — acetaminophen for headache, for example, or antiemetics for nausea.

When ingested in significant amounts, histamine causes a classic allergic response, usually within 30 minutes. Flushing, palpitation, headache, nausea, and diarrhea are the most common symptoms, but the patient may also experience tachycardia, wheezing, and fluctuation in blood pressure. A distinctive rash — described as bright red, hot, and itchy — develops on the face, neck, chest, and back, but unlike an allergic reaction, there is no whealing.² Symptoms usually persist for about three hours, but the patient may take longer to recover in severe cases — up to eight hours.

Treatment options include the following:

• Administration of diphenhydramine (Benadryl) 50mg IV/IM/PO every six hours as directed⁵
• Possible administration of an H2 receptor blocker, such as ranitidine or cimetidine, twice daily to reduce stomach acidity
• Possible emesis, especially in severe cases⁴
• Administration of supportive care (ECGs for tachycardiac patients, chest x-rays for related respiratory discomfort, and supplemental oxygen for any associated shortness of breath)

In severe cases, it may be necessary to continue antihistamines for several days. Options to consider include cetirizine, loratadine, and fexofenadine.²

Also, activated charcoal may be beneficial if given early or if the patient has eaten a great deal of fish.

Oral antihistamines are quite effective in most scombroid poisoning cases since symptoms tend to resolve quickly — within 10 to 15 minutes of taking a quick-acting antihistamine tablet.²

The importance of obtaining a thorough patient history cannot be overstated. While most scombroid poisoning occurs within minutes after ingestion, some reactions have been documented as far out as two hours following the meal. Obviously, it’s important to find out the patients’ food intake over the course of several hours, as well as the source of the food — local
fisheries, restaurants, or the patient’s own freezer or refrigerator.

Symptoms may be more severe in patients taking certain medications that retard the liver’s breakdown of histamine, such as isoniazide and doxycycline.¹ In general, people with weakened immune systems or liver problems should not eat raw seafood because of the higher risk of toxic infection. Patients with comorbid illnesses like coronary artery disease risk acute coronary syndromes caused by the tachycardia and hypotension associated with severe cases of scombroid poisoning.⁶

Remember: Scombroid poisoning is not an allergic reaction (anaphylaxis). Thus, it does not require the traditional adrenaline injections or corticosteroid dose packs. Nor is scombroid poisoning an infection; antibiotics therefore have no effect on symptoms. As noted earlier, most episodes are successfully treated with quick-acting conventional antihistamine tablets.

What the patient needs to know

Patient education should emphasize that if freshly caught fish won’t be frozen soon after being caught, it should immediately be refrigerated and eaten the same day. What’s more, patients should be taught that while affected fish may have a peppery taste, a normal taste does not guarantee safety.²

With fish bought at a supermarket or butcher, all purchases should be kept on ice or refrigerated at colder than 38 F to prevent spoilage.¹ Patients should also be told to avoid eating finfish or shellfish sold as bait, since such products aren’t required to meet the same food safety
regulations as seafood for human consumption. Additionally, it’s wise to urge patients to check with local health officials before collecting shellfish and look for any state or local health department advisories posted at fishing supply stores.

Get the word out

It’s important that health care staff notify the proper authorities of any suspected marine toxin cases so that officials may investigate whether a restaurant, oyster bed, or fishing area has posed a recurrent problem.

And while the health department can report issues and activities specific to your area, the Centers for Disease Control and Prevention in Atlanta is an invaluable source for information — the agency publishes the Morbidity and Mortality Weekly Report, which can be viewed at www.cdc.gov/mmwr.

Patients also need education regarding food consumed while traveling outside the country. They should be advised to avoid cooked food that has been kept at room temperature for several hours — and then only if food has been thoroughly cooked and is still hot when brought to the table. They should always avoid food bought from street vendors. It’s also wise to get information from local health agencies about any concerns over fish-related biotoxin occurrences in their area.⁷

A final cautionary note: Scombroid poisoning in most cases is likely to be less a hazard than an inconvenience, one that is quickly and easily treated with an antihistamine and, in some cases, activated charcoal. But for those with a compromised immune system or liver disease, the risks are much more severe. Making sure that such patients understand those risks is every nurse’s responsibility.

*Composite patient.

Maureen G. Sullivan-Tevault, RN, CEN, works in the pain management department at the VA Medical Center in Bay Pines, Fla.

References

1. Marine Toxins. Centers for Disease Control and Prevention Website. Available at: www.cdc.gov/ncidod/dbmd/diseaseinfo. Accessed January 17, 2005

2. New Zealand Dermatological Society Incorporated. Scombroid Fish Poisoning. Available at: http://dermnetnz.org/reactions/scombroid.html. Accessed January 17, 2005.

3. Otwell WS. Scombroid Poisoning. Available at: www.tidewater foodservice.com. Accessed January 18, 2005.

4. Plantz SH.Wilderness: Scombroid Poisoning. Available at: www.emedicinehealth.com/articles/27938-6.asp. Accessed January 18, 2005.

5. Moses S. Scombroid Fish Poisoning. Available at: www.fpnotebook.com/ER46.htm. Accessed January 18, 2005.

6. Noltkamper D. Toxicity, Marine–Histamine in Fish. Available at: www.emedicine.com/ped/topic1012.html. Accessed January 18, 2005.