2. STATISTICS ON SEAFOOD-BORNE DISEASES

The true incidence of diseases transmitted by foods is not known. There are many reasons for this. In most countries there is no obligation to report on food borne diseases to public health authorities. In the few countries which have a reporting system there is severe underreporting. It has been estimated that as few as 1% of the actual cases of food borne diseases are recorded (Mossel 1982). This is because neither the victim nor the physician are aware of the etiological role of foods. Furthermore, the food responsible is often not available for analysis and the true vehicle for the disease agent is not identified. The statistics below are therefore only for identifying trends and areas of concern.

Between 1973 and 1987 a total of 7,458 foodborne disease outbreaks involving 237,545 cases were reported in the United States (Bean and Griffin 1990). A specific food vehicle was identified in only 3699 (50%) of the outbreaks. Of these food items seafood was the food most frequently associated with disease as shown in Table 2.1.

1) An incident is an outbreak (2 or morepersons become ill) or a single caseinvolving one person.
2) Data from Bean and Griffin (1990)
3) Data from Todd (1989a)
4) Data from Beckers (1986)
5) Total of incidents for whichvehicles were identified

In the 2-year period (1980–1981) 8.7% of all outbreaks in the Netherlands were seafood-borne (Beckers 1986). However, Turnbull and Gilbert (1982) pointed out that specific foods are frequently not identified in food-poisoning incidents, but where they have been, fish and shellfish are implicated in less than 3% of all the general and family outbreaks reported in Britain. The incidence rates reported above should be evaluated in the light of total food consumption. Thus, in the same period in the U.S.A., the meat consumption was approx. 10 times that of fish and consumption of poultry approx. 5 times that of fish (Valdimarsson 1989).

The etiological agents associated with the large number of foodborne disease outbreaks reported in the USA in the period 1973–1987 are shown in Table 2.2.

In the majority of outbreaks (62% of total) the disease agent was not identified. One reason for this could be lack of proper technique for identification of e.g. virus. When identification of the etiological agent has been successful, pathogenic bacteria are by far the most frequent disease agent identified.

Diseases associated with various types of seafood over the period 1970–84 have been analyzed by Bryan (1980, 1987). He found that “fish” was most frequently involved followed by bivalve molluscan shellfish and crustaceans. Unfortunately, the reports available do not include information on the type of seafood products which were vehicles for the disease outbreaks. Knowledge of the preservation principles involved (a_w, pH, smoke, preservatives etc.), packaging and preparation before eating (cooking) would have been very useful in evaluation of the hazards related to the various types of seafood.

A considerable number (18%) of disease outbreaks related to “fish” recorded in the U.S. were of unknown etiology (see Figure 2.1). Most common were intoxications related to biotoxins (ciguatera) and histamine, which accounted for two thirds of all recorded outbreaks. The rest (18%) were caused by various bacteria, parasites, virus and chemicals.

1) This group includes: Staphylococcal intoxication Shiegellosis Anisakiasis C. porfringens gastroenteritis Salmonellosis Strept. pyogenes infection Fish tae worm Cholera Typhoid fever Pufferfish poisoning V.parahaem. gastroenteritis Hepatitis Non-B Chemical poisoning

Figure 2.1. Diseases transmitted by fish in the United States from 1970 to 1984. (No. of outbreaks; %). Data from Bryan (1980) and Bryan (1987).

A total of 157 outbreaks of seafood borne diseases in the U.S. were related to consumption of molluscs. The great majority of them were of unknown etiology (see Figure 2.2). This fact should be viewed in the light of the great difficulties in diagnosing some of the viral diseases. Although only a few of the outbreaks recorded in Figure 2.2 are related to virus, there is no doubt that most illness associated with molluscs is mainly of viral origin.

Crustaceans were implicated as vehicle in a total of 63 outbreaks in U.S. during 1970– 1984. More than one third of the outbreaks were of unknown etiology, but when the disease agent was identified, it was always a pathogenic bacterium (see Figure 2.3).

In a later study, Bean and Griffin (1990) analyzed the etiologic agents and food vehicles associated with 7,458 outbreaks (involving 237,545 cases) of foodborne diseases reported to Center for Disease Control, U.S.A. between 1973 and 1987. The disease agent was identified in only 2,841 outbreaks as shown in Table 2.2.

2) This group includes: Staphylococcal intoxication Shigellosis Hepatitis A Salmonellosis Streptococcal infection E. coli gastroenteritis Cholera A.hydrophilaie B. cereus gastroenteritis Hepatitis Non-B

Figure 2.2. Diseases transmitted by molluscs in the United States from 1970 to 1984. (No. of outbreaks; %). Data from Bryan (1980) and Bryan (1987).

3) This group includes: Shigellosis A. hydrophila Salmonellosis C. perfringens gastroenteritis Cholera non-01 gastroenteritis B. cereus gastroenteritis

Figure 2.3. Diseases transmitted by crustaceans in the United States from 1970 to 1987. (No. of outbreaks; %). Data from Bryan (1980) and Bryan (1987).

The data in Table 2.3 confirm that seafood borne diseases transmitted by finfish first of all are related to biotoxins and bacterial pathogens, while in the majority of shellfish transmitted diseases the disease agent has not been identified, but are probably viral.