The Centre for Health Protection is investigating three food poisoning cases involving four people, suspected to be caused by fish containing ciguatoxin.

A 55-year-old man and three women aged five to 37 developed ciguatoxin symptoms, including limb numbness, diarrhoea, abdominal pain and vomiting after eating coral reef fish at home on May 27, May 31 and June 1. None were hospitalised.

The grouper fish was bought from markets in Choi Wan Estate in Ngau Tau Kok and Smithfield Road in Kennedy Town, and from a fish hawker in Kwun Tong.

To prevent ciguatera fish poisoning:

* eat less coral reef fish;

* eat a small amount of coral reef fish at any one meal and avoid having a whole fish feast in which all the dishes come from the same big fish;

* avoid eating fish head, skin, viscera and roe, which usually have higher concentrations of toxin; and,

* when eating coral reef fish, avoid consuming alcohol, peanuts or beans as they can aggravate the poisoning.

Seek medical treatment immediately if symptoms appear.