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An outbreak of severe food poisoning in Sacramento, California, that left nine people in hospital has been linked to cheese sauce sold on nacho crisps at a family-run petrol station.

Health officials have stopped Valley Oak Food and Fuel selling food.

Cases of botulism, a rare and sometimes fatal form of food poisoning, were first reported on 5 May and in total nine people are confirmed to have it.

One of the victims is reportedly so ill she cannot speak or keep her eyes open.

Dr Oliva Kasirye of the Sacramento County Public Health Department told reporters that preliminary testing showed the cheese was carrying botulism.

The family of one of the affected patients has already filed a lawsuit against the petrol station, claiming neglect.

Botulism poisoning is caused by toxins released by a type of bacteria called Clostridium botulinum.

Human digestive processes cannot break down the toxic chemical, which moves to the nervous system. Symptoms emerge in adults 18-36 hours after eating contaminated food.

In this case, it is thought the nacho cheese sauce may have been canned. Tinned food is a risk for botulism because the bacterium grows best when there is no oxygen around.

In adults, symptoms - including difficulty walking or swallowing, impaired vision and potential convulsions or paralysis - will emerge between 18 and 36 hours after eating the contaminated food.

Depending on how quickly botulism is detected and how much of the bacterium has been swallowed, botulism may be treated with an anti-toxin drug.