Staphylococcus aureus
·
It is said to be the commonest cause
of bacterial food poisoning.
·
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.
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.
·
Oral: 1 to 6 hours.
·
Inhalation: 3 to 12 hours.
·
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.
·
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.
·
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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