Food poisoning due to bacteria

Organism Food poisoning can either be due to bacteria, viruses, organic or inorganic poisons (Table 9.1). The most common poisoning is that produced by bacteria. The main types of bacterial food poisoning are due to Salmonella, Staphylococcus or Clostridia.

Clinical features Due to the similarity of presentation, it is more convenient to consider them as a group, rather than individually. Onset is sudden with fever, generally vomiting and/or diarrhoea in a family or group of persons who have shared the same meal. Sometimes, a sub-normal temperature or lowered blood pressure is the presenting symptom. The incubation period is very short and sufficiently precise for the type of food poisoning to be suspected by the length of time since the food item was eaten.

Incubation period With staphylococcal food poisoning, it is between 1 and 6 h; Salmonella over 6h, usually 12-36 h, and for Clostridia, 12-24 h or several days. Less commonly, food poisoning can be due to Bacillus cereus (1-12 h) and Vibrio parahae-molyticus (12-48 h).

Transmission is through the consumption of food contaminated with the bacteria or its toxins. Infection can sometimes result from a contaminated water supply and via milk that has not been pasteurized. Salmonella generally infects the food in the living state, such as cattle, poultry or eggs, but unhygienic practice in the slaughtering of animals or preparation of foodstuffs can also be responsible. The bacteria are killed by proper cooking and no toxins are produced; so examination of the meal should reveal an improperly cooked source.

Staphylococcal food poisoning results from toxin produced by the bacteria so the

Table 9.1. Food poisoning.

Agent

Period of onset (h) Symptoms

Types of food

Bacterial food poisoning

Staphylococcal 1-6

B. cereus 1-12 Salmonella 12-36

C. perfringens 9-24

C. botulinum 9-24

V. parahaemolyticus 12-48

Fish poisoning

Ciguatera 1-30

Scombroid 1-12

Tetraodontoxins 0.5-3

Shellfish, paralytic 0.5-3

Shellfish, diarrhetic 0.5-3

Plant foods

Akee (Blighia sapida) 2-3

Cassava (Cyanide) Hours

Contaminants

Triorthocresyl- Days phosphate

Sudden, vomiting more than diarrhoea Vomiting, diarrhoea and fever Abdominal cramps, diarrhoea, shock Ptosis, dry mouth, paralysis Abdominal pain, diarrhoea and fever

Parathesiae, malaise, sweating, diarrhoea and vomiting Burning sensation, nausea, vomiting Hypersalivation, vomiting, parasthesiae, vertigo, pains

Parasthesiae and paralysis Diarrhoea and vomiting

Vomiting, convulsions, death Vomiting, diarrhoea, abdominal pain, headache, coma

Neuropathy

Stored food

Improperly cooked meat, eggs and milk produce Cooked meat, especially pig

Preserved foods Undercooked or raw fish

Barracudas, snappers, sea bass, groupers

Tuna, mackerel, salmon or cheeses Puffer fish

Clams and mussels Clams, scallops, etc.

Unripe fruit

Improperly processed root Cooking oil food may be adequately cooked and no bacteria isolated from the suspected food source. It is commonly transmitted by food handlers with an infected lesion or unhygienic habits, such as transferring bacteria from the nose. V. parahaemolyticus is particularly associated with seafood or food that has been washed with contaminated seawater.

Clostridia food poisoning can be caused by several types of organisms. C. botulinum infection results in a severe disease, botulism, which is characteristic of home-preserved foods (see further Section 18.5). C. perfringens generally produces a mild dis ease of short duration, but in New Guinea and the Western Pacific Islands, it is responsible for enteritis necroticans or pigbel, in which there is an acute necrosis of the small and large intestines with a high fatality rate. This is associated with feasting, generally of pig meat, but also from other animals such as cattle. Children, particularly boys, are mainly affected. The disease is probably accentuated by a protease inhibitor contained in sweet potato, preventing breakdown of the toxin.

Clostridia have resistant spores, which can remain in the soil for long periods, and their contamination of partly cooked and re-heated food allows multiplication and production of the toxin.

There is often a seasonality of food poisoning, Salmonella in the summer months and C. jejuni in spring and autumn. C. perfringens occurs throughout the year.

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