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Botulism after eating smoked fish

16/2000, 10.08.2000

Joint press release by the Robert Koch Institute and the Federal Institute for Health Protection of Consumers and Veterinary Medicine

In Europe there are repeatedly cases of poisonings caused by foods contaminated with Clostridium botulinum germs. In North Rhine-Westphalia three people recently fell ill after eating vacuum-packed smoked trout caused by botulism. The Federal Institute for Health Protection of Consumers and Veterinary Medicine recommends to manufacturers and consumers that vacuum-packed smoked fish should always be stored at temperatures below 7 degrees Celsius, if possible below 3 degrees Celsius as this is the only way of preventing the multiplication of clostridia. Major increases in temperature during transport and sale are to be avoided.

Botulism is the name given to the disease which is triggered by the neurotoxin (a substance which damages nervous tissue) of the bacteria Clostridium botulinum. In the case of a foodborne botulism infection, symptoms occur between 12 and 36 hours after intake. They include nausea, diarrhoea or constipation and also neurological symptoms. Depending on the amount of toxin taken in, there may be dryness of the mouth, optic dysfunction (double images, blurred vision, photophobia), dysphagia, acute ocular muscle paralysis and also rapidly progressing, symmetrical descending atonic paralysis. The patients are fully conscious. Botulism antitoxins should be administered as soon as possible and supporting intensive medical care treatment given. There is no evidence of a transmission of Clostridium botulinum from one human being to another.

Clostridia are widespread in soil and in coastal waters. Cases of illness occurred in the past following the consumption of tinned vegetables, meat, fish and fruit products. Home preserves are thought to be particularly critical as the temperatures reached during bottling are normally not sufficient to kill the spores. For 1999 up to now 19 cases of disease have been reported to the Robert Koch Institute, two of them with a fatal outcome. According to § 3 Federal Epidemics Act cases of suspicious of botulism, disease and deaths are notifiable.

Given the widespread occurrence of Clostridium botulinum, it is not possible to completely avoid the natural contamination of fish and other foods. During processing and storage, handling must be undertaken in a very cautious and hygienic manner so as to avoid a multiplication of the germs and the formation of toxins. Fish should be gutted immediately after being caught and washed immediately prior to any processing. This reduces the spore burden and increases the effectiveness of all further preserving methods.

The risk of botulism from fresh fish and other raw, untreated foods is extremely low. When using preserving methods like pickling, smoking or marinating, clostridia may multiply under certain circumstances when the methods are used "non-aggressively" and only low salt and smoke or high humidity contents are reached. If in addition a product is vacuum-packed, this can increase the risk further. Particular attention and care should be paid to preserving methods and also during the home production of smoked goods. Ongoing refrigeration is the most reliable protection against clostridia in all smoked products.

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