Four people have fallen ill with food poisoning believed to have been caused by fish containing ciguatoxin.

On November 19 a 35-year-old woman and a four-year-old girl suffered numbness and diarrhoea after eating grouper in an Eastern District restaurant. The woman was admitted to Pamela Youde Nethersole Eastern Hospital in stable condition and the girl did not need hospitalisation.

The second case occurred on the same day and involved a 48-year-old woman and an 11-year-old boy. They developed similar symptoms after consuming grouper in the same restaurant. Neither required hospitalisation.

Ciguatera poisoning is mainly associated with the consumption of a big coral reef fish which has accumulated the toxin in its body, particularly the internal organs. It is not easy to tell from the appearance of the fish if it contains the toxin, which cannot be destroyed by cooking.

People affected may show symptoms of numbness of the mouth and the limbs, vomiting, diarrhoea and pain of the joints and muscles. Most recover without long-term health effects. However, if excessive toxin is consumed, the circulatory and nervous systems can be affected.

To prevent ciguatera poisoning:

* coral reef fish should be purchased from reputable and licensed seafood shops. Do not buy it when the source is doubtful;

* eat less coral reef fish, especially fish weighing over three catties;

* eat small amounts of coral reef fish at any one meal;

* avoid eating the head, skin, intestines and roe of coral reef fish which usually have a higher concentration of toxin;

* when eating coral reef fish avoid consuming alcohol, peanuts or beans as they may aggravate the poisoning; and,

* seek medical treatment immediately should symptoms of ciguatoxin fish poisoning appear.