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Types of food poisoning - Staphylococcal food poisoning
Food poisoning
Food poisoning is an acute gastroenteritis caused by ingestion of food or drink contaminated with either living bacteria or their toxins or 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
Food poisoning may be of two types: non-bacterial and bacterial.
(a) 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.
(b) Bacterial: 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. 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 house- hold detergents interfering with sewage treatment, and
- (e) wide distribution of "prepared foods".
(a) AGENT(S): The species most often incriminated in human outbreaks are S. typhimurium, S. cholera-suis and S. enteritidis, besides many others.
(b) 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. Rats and mice are another source; they are often heavily infected and contaminate foodstuffs by their urine and faeces. Temporary human carriers can also contribute to the problem .
(c) INCUBATION PERIOD: 12 to 24 hours commonly.
(d) 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 diarrhoea which usually lasts 2-3 days. Mortality is about 1 per cent. A convalescent carrier state lasting for several weeks may occur. Salmonellosis is described in detail separately.
Staphylococcal food poisoning
It is about as common as salmonella food poisoning.
(a) AGENT: Enterotoxins of certain strains of coagulase- positive Staphylococcus aureus. At least 5 different enterotoxins have been identified, and a sixth may exist. Toxins can be formed at optimum temperatures of 35 deg. to 37 deg. C. These toxins are relatively heat stable and resist boiling for 30 minutes or more.
(b) 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.
(c) 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 ("intradietetic" toxins). Since the 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 diarrhoea. In severe cases, blood and mucus may appear. Unlike salmonella food poisoning, staphylococcal food poisoning rarely causes fever. Death is uncommon.