Information Note for
Provisional Legislative Council
Panel on Health Services
9 February 1998
Ciguatera Fish Poisoning
In January 1998, 34 cases of ciguatoxin poisoning, arising from consumption of ciguatera contaminated fish, were reported to Department of Health. A total of 172 people were affected. This paper provides information on this subject.
Cases of Ciguatera Fish Poisoning
2.Ciguatoxin has been known for over a hundred years as a cause of food poisoning and is the third most common cause of such in Hong Kong - after pesticides and bacteria. In the last five years, there were 85 cases with 408 people affected. None of these cases has caused death to the affected. Details are as follow -
3.Ciguatoxin develops naturally and is heat-stable. It is produced by a marine microorganism - the dinoflagellate called Gambierdiscus toxicus - which attaches to dead coral surfaces and algae, and may be passed up the food chain - from small fish to large predatory fish and, finally, to man. The toxin may not always be present in a fish at toxic level, but it can build up over time. Larger reef fish are more likely to contain larger doses. The existence and proliferation of the microorganisms appear to be related to disturbances in the reef environment.
4.Compilation of a comprehensive list of fish that may give rise to ciguatera poisoning is not feasible because it is estimated that over 400 species may be involved. According to past records of ciguatera poisoning cases in Hong Kong, the species of coral reef fish which are more likely to contain ciguatoxin include Black Fin Red Snapper, Mangrove Snapper, Tiger Grouper, Humphead Wrasse, Giant Grouper and Flowery Cod. The larger the reef fish, the more likely it is that it may contain toxic level of ciguatoxin.
5.AFD has advised that of the 28 000 tonnes of live marine fish consumed in 1997, some 80% were cultured in Hong Kong and overseas. Hence, these were ciguatera-free. Reef fish accounted only for some 8% of the 28 000 tonnes. Comparing the number of ciguatera poisoning cases with the quantity of reef fish consumed, it is evident that only a small fraction of reef fish was contaminated. It will not be appropriate to impose a ban on the import of live reef fish.
6.Affected fish cannot be identified by inspection, taste, texture or smell. With current technology, quick and reliable screening testing procedures are not yet available.
7.As for food analysis, the toxin can be recovered from toxic fish through tedious extraction procedures. The mouse test performed with the assistance of Department of Zoology, The University of Hong Kong is a universally accepted method of establishing toxicity in suspected fish. Such a method, however, is time-consuming and not accurate enough to prove the presence of ciguatoxin. However, we have recently learnt that a test kit for rapid screening is being developed in the USA.
8.Manifestations of ciguatoxins in human usually involve a combination of bowel, heart and nerve disorders. Diagnosis is based on symptoms and recent dietary history.
9.In all places where fish forms an important part of the diet, ciguatera poisoning is an issue of public health and economic concerns. However, medical evidence has shown that most cases are self-limited, although in the most serious cases, the toxin level may be sufficient to cause dealth.
10.Avoiding consumption of fish of the types specified in para. 4 is the best way to avoid ciguatera fish poisoning. Other safeguard measures include -
--avoiding certain parts of the fish at which the toxin is concentrated e.g. the head, the liver, the gonads and the roe;
--avoiding intake of alcohol and nuts when consuming reef fish as the former can aggravate the symptoms should intoxication occur; and
--those who have experienced the illness before ought to refrain from consuming reef fish again as recurrence is more likely and symptoms to be more severe.
11.To enhance public awareness of the ciguatera fish poisoning, Department of Health will continue to distribute relevant pamphlets to the seafood trade, seafood importers, owners of restaurants and members of the public, providing them with background information on ciguatera poisoning. The information has also been included in the pre-recorded health education telephone programme. Department of Health will collaborate with Agriculture and Fisheries Department to devise new TV and radio announcements on the same subject.
12.Surveillance of ciguatera poisoning cases by Department of Health will continue with the assistance of Agriculture and Fisheries Department. Timely messages will be disseminated in case of unusual findings. We shall also keep in view the development of the quick field screening test in the USA and when it is available, examine the feasibility of adopting it in Hong Kong.
Health and Welfare Bureau
9 February 1998