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Food poisoning may be of the following two types:
Non–bacterial
It is caused by chemicals such as arsenic, certain plant and sea foods, etc. In recent years, there has been a growing concern about contamination of food by chemicals, eg. fertilizers, pesticides, cadmium and mercury.

Bacterial
It is caused by the ingestion of foods contaminated by living bacteria or their toxins. The conventional classification of bacterial food poisoning into toxic and infective types is becoming increasingly blurred with the knowledge that in some types, both multiplication and toxin production are involved.

Bacterial food poisoning may be of the following types:
Salmonella Food Poisoning
An extremely common form of food poisoning. The following reasons have been indicated for its increase in recent years:
An increase in communal feeding.

Source
Salmonellosis is primarily a disease of animals. Humans contract the infection from farm animals and poultry – through contaminated meat, milk and milk products, sausages, custards, egg and egg products. Rats and mice are another source; they are often heavily infected and contaminate foodstuffs by their urine and feces. Temporary human carriers can also contribute to the problem.

Incubation Period
About 12–24 hours, commonly.

Mechanism of Food Poisoning
The causative organisms, on ingestion, multiply in the intestine and give rise to acute enteritis and colitis. The onset is generally sudden with chills, fever, nausea, vomiting, and a profuse watery diarrhea which usually lasts for 2–3 days. The mortality rate is about 1 per cent. A convalescent carrier state lasting for several weeks may occur.



Staphylococcal Food Poisoning
Staphylococcal Food Poisoning
It is about as common as Salmonella food poisoning. The reasons indicated for its occurrence are as follows:

Agent
Enter toxins of certain strains of coagulase–positive Staphylococcus Aureus. At least, 5 different enter toxins have been identified, and a sixth may exist. Toxins can be formed at optimum temperatures of 35 deg. to 37deg. C. These toxins are relatively heat–stable and resist boiling for 30 minutes or more.

Source
Staphylococci are ubiquitous in nature, and are found on the skin and in the nose and throat of men and animals. They are a common agent of boils and pyogenic infections of man and animals. Cows suffering from mastitis have been responsible for outbreaks of food poisoning involving milk and milk products. The foods involved are salads, custards, milk and milk products which get contaminated by staphylococci.

Incubation Period
It’s about 1–6 hours. The incubation period is short because the “Preformed” toxins act directly on the intestine and CNS. The illness becomes manifest by the sudden onset of vomiting. Unlike Salmonella food poisoning, Staphylococcal food poisoning rarely causes fever. Death is uncommon.

Botulism
It is most serious but rare. It kills two–thirds of its victims!

Agent
Exotoxin of Clostridium Botulinum generally Type A, B, or E.

Source
The organism is widely distributed in soil, dust and the intestinal tract of animals and enters food as spores. The foods most frequently responsible for botulism are home preserved foods such as home–canned vegetables, smoked or pickled fish, home–made cheese and similar low acid foods. In fact, botulism derives its name from the Latin word for sausage (botulus).

Incubation Period
About 12–36 hours.

Mechanism of Food Poisoning
The toxin is preformed in food (intradietetic) under suitable anaerobic conditions. It acts on the parasympathetic nervous system. Botulism differs from other forms of food poisoning in that the gastrointestinal symptoms are very slight. The prominent symptoms are dysphagia, diplopia, ptosis, dysarthria, blurring of vision, muscle weakness and even quadriplegia. Fever is generally absent, and consciousness is retained. The condition is frequently fatal, death occurring 4–8 days later due to respiratory or cardiac failure. Since the toxin is thermo labile, the heating of food which may be subjected to 100 deg. C for a few minutes before use will make it quite safe for consumption.

Botulism occurring in infants is called “Infantbotulism”. It is due to infection of the gut by CI Botulinum with subsequent in vivo production of toxin.

Anti–toxin is of considerable value in the prophylaxis of botulism, when a case of botulism has occurred, anti–toxin should be given to all individuals partaking of the food. The dose varies from 50,000 to 1,00,000 units. The anti–toxin will be of no avail if the toxin is already fixed to the nervous tissue. Guanidine Hydrochloride reverses the neuromuscular block of botulism. When combined with good medical and nursing care, the drug can be a useful adjunct in the treatment of botulism. Active immunization with botulinum toxoid to prevent botulism is also available.



CI Perfringens Food Poisoning
CI Perfringens Food Poisoning
Agent
CI Perfringens (Welchii).

Source
The organism has been found in feces of humans and animals, and in soil, water and air. A majority of outbreaks have been associated with the ingestion of meat, meat dishes and poultry. The usual story is that the food has been prepared and cooked for 24 hours or more before consumption, and allowed to cool slowly at room temperature and then heated immediately prior to serving.

Incubation Period
About 6 to 24 hours, with a peak from 10 to14 hours.

Mechanism of Food Poisoning
The spores are able to survive cooking, and if the cooked meat and poultry are not cooled enough, they will germinate. The organisms multiply between 30 deg. C. and 50 deg. C. and produce a variety of toxins, e.g. alpha toxin, theta toxin, etc. Prevention consists either by cooking food just prior to its consumption or, if it has to be stored, by rapid and adequate cooling.

Clinical Symptoms
The most common symptoms are diarrhea, abdominal cramps and little or no fever, occurring 8 to 24 hours after consumption of the food. Nausea and vomiting are rare, illness is usually of short duration, usually one day or less. Recovery is rapid and no deaths have been reported.

B Cereus Food Poisoning
Bacillus Cereus is an aerobic, spore–bearing, motile, gram positive rod. It is ubiquitous in soil, and in raw, dried and processed foods. The spores can survive cooking and germinate and multiply rapidly when the food is held at favorable temperatures. B Cereus has been recognized as a cause of food poisoning with increasing frequency in recent years.

Recent work has shown that B. Cereus produces at least two distinct enter toxins, causing two distinct forms of food poisoning . One, the emetic form with a short incubation period (1–6 hours) characterized by predominant upper gastro–intestinal tract symptoms, rather like Staphylococcal food poisoning, characterized by predominantly lower intestinal tract symptoms like CI Perfiringens food poisoning (diarrhea, abdominal pain, nausea with little or no vomiting and no fever). Recovery within 24 hours is usual. The toxins are preformed and stable. Diagnosis can be confirmed by isolation of 10 deg. of more B. Cereus organisms per gram of epidemiologically incriminated food. Treatment is symptomatic.

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