Beware of seafood poisoning
A study conducted by Tygerberg Poisons Information Centre found that there is an increase in seafood poisoning calls in autumn (March to May). In South Africa, red tides usually occur in late summer and autumn. One possible reason for the relatively high occurrence of scombroid poisoning might be linked to the uniquely South African tradition of serving pickled fish on Good Friday, which usually occurs during autumn. The increase in demand for fish during this period could relate to a break in the cold chain from vendors, and improper refrigeration on the user’s side.
Scombroid poisoning (also known as histamine food poisoning) is caused by the consumption of ‘spoiled fish’. Inadequately stored fish could contribute to the high levels of histamine formed by bacteria that break down endogenous histidine to histamine. Many of the fish that cause histamine poisoning are large pelagic species that continuously swim at a high speed.
The Cape yellowtail is an example of a red-muscled fish and most commonly the fish responsible for scombroid poisoning in South Africa. The ‘scombrotoxins’ and histamine are heat stable and scombroid poisoning will develop after ingestion of cooked, smoked or canned fish. The onset of scombroid poisoning is rapid.
Skin manifestations are the most prominent and appear in minutes and usually do not last for more than six hours. Patients experience a hot, blotchy, flushing skin with well-demarcated borders, especially in the face, neck and upper chest area. Diarrhoea may be prominent and usually appears within six hours. Other non-skin features include palpitations, headache, vomiting and abdominal cramps. A tingling sensation around the mouth and in the legs and a scratchy feeling in the throat may occur in up to 20% to 40% of patients. Initially, a peppery taste may be experienced. Patients with a history of asthma or allergies may develop difficulty in breathing or shortness of breath. Many of these symptoms and signs resemble that of a food allergy and patients are often incorrectly told that they have a ‘seafood allergy’ and inappropriately informed to refrain from eating seafood.
During the last 25 years, two different types of shellfish poisonings were managed by the Tygerberg Poisons Information Centre:
- Paralytic shellfish poisoning: Within 30 minutes to two hours after ingestion of the contaminated shellfish, patients present with a tingling sensation and spreading numbness, starting around the lips to the face and neck. A prickly sensation develops in the fingertips and toes. Visual disturbances, vertigo, dizziness, ataxia, headache, a floating or gliding sensation, nystagmus, dysphagia and dysarthria are common symptoms. In severe cases, progressive muscular paralysis with difficulty in breathing develops. Deaths have been reported within two to 24 hours post ingestion.
- Diarrhetic shellfish poisoning: This results in severe gastroenteritis and fluid loss. The patient presents with nausea, vomiting, diarrhoea and abdominal pain within four hours after consumption of contaminated shellfish.
Shellfish and scombroid toxins are heat stable and will not be destroyed by normal cooking processes. A serious complication of paralytic shellfish poisoning is respiratory failure.
Who to contact:
The Western Cape Poison Information Helpline (0861 555 777) in South Africa should be contacted for free telephonic advice on local marine envenomation and poisoning.