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Chapter: Modern Medical Toxicology: Food Poisons: Food Poisoning

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Staphylococcus aureus - Microbial Food Poisoning

It is said to be the commonest cause of bacterial food poisoning.

Staphylococcus aureus

·              It is said to be the commonest cause of bacterial food poisoning.

Source

·      Previously cooked, proteinaceous food: meat, fish, milk, and milk products. Staphylococcal toxins are formed within few hours when food is kept at room temperature.

o     Most foods (particularly those high in protein) will support staphylococcal growth, especially custard or cream filled pastries, mayonnaise, ham, and dairy, poultry, potato and egg products.

o     Pasteurising milk will kill the bacteria, but unfortu-nately will not inactivate the toxins.

o     Other sources include canned mushrooms, rice, noodles, salads, and cooked food that has been left at room temperature.

·      Common carriers of Staphylococcus aureus comprise food handlers (especially those with purulent secretions or nasal discharge).

·      While most Staphylococcus aureus strains implicated in food poisoning have been coagulase-positive, outbreaks with coagulase-negative species have been reported.

Toxin

Relatively heat-stable enterotoxins (A, B, C1-3, D, E, and H). The commonest type is A. Enterotoxin B (SEB), a pyrogenic toxin, also commonly causes food poisoning after ingestion of improperly prepared or handled food material. It causes a significantly different clinical syndrome when inhaled than when ingested. The toxin is extremely potent and stable, and may be used as a bioterrorism agent. Only a small amount of toxin (approximately 200 ng) is required to cause clinical illness. However, large numbers of organisms must be present in food in order to produce enough enterotoxin to cause illness, (106 organisms/gm or more). Aerosol-incapacitating dose amounts to about 30 ng/person; lethal dose is approximately 1.7 mcg/person.

Incubation Period

·      Oral: 1 to 6 hours.

·      Inhalation: 3 to 12 hours. 

Clinical Features

·      Nausea and vomiting with violent retching, diarrhoea, crampy abdominal pain. Diarrhoea is usually mild, while vomiting is severe.

·      Fever is usually absent.

·      Headache, weakness, and dizziness may be present.

·      Inhalation of the toxins can cause sudden onset of fever, headache, chills, myalgia, non-productive cough, dyspnoea, and retrosternal chest pain. Nausea, vomiting, and diarrhoea may occur as a result of inadvertent swallowing of the toxin. Conjunctival congestion may be present. Postural hypotension could develop due to fluid losses.

Diagnosis

·      Staphylococcal food poisoning is usually a self limited illness; often no laboratory evaluation is required. Monitor electrolytes and fluid balance in patients with significant volume loss from vomiting and diarrhoea.

·      Serological tests are usually very sensitive, for e.g. latex agglutination and ELISA.

·      Radioimmunoassay can detect as little as 0.1 ng to 1.0 ng toxin/gm of food.

Treatment

·      Supportive measures.

·      The illness usually lasts for no more than 20 to 24 hours, and is self-limiting.

·              All persons with significant toxicity, dehydration, abnormal electrolyte levels, or a history of poor compliance should be admitted for intravenous fluid therapy. Significant nausea and vomiting can be controlled with an antiemetic agent. However, antiemetics are not usually required if alteration of the diet is successful.

·              Inhalation exposure:

o     Move patient from the toxic environment to fresh air.

o     Monitor for respiratory distress. If cough or difficulty in breathing develops, evaluate for hypoxia, respiratory tract irritation, bronchitis, or pneumonitis.

o     Administer 100% humidified supplemental oxygen, perform endotracheal intubation, and provide assisted ventilation as required.

o     Administer inhaled beta adrenergic agonists if bron- chospasm develops.

o     Exposed skin and eyes should be flushed with copious amounts of water.

 

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