Food poisoning: types and their features

Food poisoning is an acute gastroenteritis caused by ingestion of food and drink contaminated with either living bacteria or their toxins and inorganic chemical substances and poisons derived from plants and animals. The condition is characterized by: (a) history of ingestion of a common food (b) attack of many persons at the same time, and (c) similarity of signs and symptoms in the majority of cases.

Types of food poisoning:

• Non-bacterial: Caused by chemicals such as arsenic, certain plant and sea foods. In recent years, there has been a growing concern about contamination of food by chemicals, e.g., fertilizers, pesticides, cadmium, mercury etc.
• Bacterial: Caused by the ingestion of foods contaminated by living bacteria or their toxins.

Salmonella food poisoning:

An extremely common form of food poisoning. Five reasons have been given for its increase in recent years :
(a) an increase in community feeding (b) increase in international trade in human food (c) a higher incidence of salmonellosis in farm animals (d) widespread use of household detergents interfering with sewage treatment, and (e) wide distribution of “prepared foods”.

AGENT:

The species most often incriminated in human outbreaks are S. typhimurium, S. cholera-suis and S. enteritidis, besides many others.

SOURCE:

Salmonellosis is primarily a disease of animals. Man gets the infection from farm animals and poultry – through contaminated meat, milk and milk products, sausages, custards, egg and egg products.

INCUBATION PERIOD:

12 to 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 2-3 days.

Staphylococcal food poisoning:

It is about as common as salmonella food poisoning.

AGENT:

Enterotoxins of certain strains of coagulase positive Staphylococcus aureus. At least 5 different enterotoxins have been identified.

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:

1-8 hours. The incubation period is short because of “preformed” toxin.

MECHANISM OF FOOD POISONING:

Food poisoning results from ingestion of toxins preformed in the food in which bacteria have grown (“intra-dietetic” toxins) toxin is heat-resistant, it can remain in food after the organisms have died. The toxins act directly on the intestine and CNS. The illness becomes manifest by the sudden onset of vomiting, abdominal cramps and diarrhea. In severe cases, blood and mucus may appear. Unlike salmonella food poisoning, staphylococcal food poisoning rarely causes fever. Death is uncommon.

Botulism:

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, homemade cheese and similar low acid foods.

INCUBATION PERIOD:

18 to 36 hours.

MECHANISM OF FOOD POISONING:

The toxin is preformed in food 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. Patients who recover do
not develop antitoxin in the blood. Since the toxin is thermolabile, 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.

Antitoxin is of considerable value in the prophylaxis of botulism. When a case of botulism has occurred, antitoxin should be given to all individuals partaking of the food. The dose varies from 50,000 to 100,000 units IV. The antitoxin will be of no avail if the toxin is already fixed to the nervous tissue. Guanidine hydrochloride given orally in doses of 15 to 40 mg/kg of body weight has been shown to reverse 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.

Cl. perfringens food poisoning:

AGENT:

Clostridium (Cl.) perfringens (welchii).

SOURCE:

The organism has been found in faeces of humans and animals, and in soil, water and air. The 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 24 hours or more before consumption, and allowed to cool slowly at room temperature and then heated immediately prior to serving.

INCUBATION PERIOD:

6 to 24 hours, with a peak from 10 to 14 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. 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 1 day or less. Recovery is rapid and no deaths have been reported.

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 2 distinct enterotoxins, causing 2 distinct forms of food poisoning. One, the emetic form with a short incubation period (1-6 hours) characterized by predominantly upper gastro-intestinal tract symptoms, rather like staphylococcal food poisoning. The other, the diarrheal form, with a longer incubation period (12-24 hours) characterized by predominantly lower intestinal tract symptoms like Cl. perfringens 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.