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Bacillus cereus in food

Bacillus cereus. Source: Mogana Das Murtey and Patchamuthu Ramasamy 

(March 2019)

Bacillus cereus (B. cereus) is a bacterium widespread in the environment.

It can form spores that are very tough and are not killed by cooking or boiling.

What illness does it cause?

There are two types of illness: emetic (vomiting) and diarrhoeal.

Neither of these illnesses are nationally notifiable (they don't need to be reported to health authorities unless there is an outbreak—linked illness in two or more people).

What are the symptoms?                                                              

For the emetic form, symptoms may include nausea and vomiting, which usually start 1 to 5 hours after eating contaminated food.

For the diarrhoeal form, symptoms may include abdominal cramps, nausea and watery diarrhoea, usually starting 8 to 16 hours after eating contaminated food.

Most people only have mild symptoms and recover quickly (within a day or less).

Who can get sick?

Anyone can get sick with B. cereus if food is highly contaminated

Symptoms can be more severe in elderly people, pregnant women, young children and people with weakened immune systems (like cancer patients).

Where does it come from?

B. cereus is widespread in the environment, and their heat resistant spores can be found in soil, plants and dry foods (such as rice and dried spices).           

Common foods linked to the emetic illness include pre-cooked starchy foods like rice, pasta and cereals.

Common foods linked to the diarrhoeal illness include pre-cooked mixed dishes, especially spiced dishes (where the opportunity for bacterial growth has occurred).

How can people get sick? 

By eating contaminated food that hasn't been properly cooked and cooled. Reheating contaminated food does not make it safer, as the bacteria's toxin is not destroyed by heat.

How can illness be prevented?

  • Cook food thoroughly and serve it immediately or keep it hot (60oC or hotter) before serving.
  • If cooked food is going to be stored to use later, cool it quickly: put it in the fridge (or freezer) as soon as it stops steaming. Divide large amounts of hot food into smaller containers to let it cool faster.
  • Keep leftovers in the fridge (or freezer) and dispose of refrigerated leftovers if not eaten within 3 or 4 days.
  • Keep hands and equipment clean when preparing and eating food.

 Image credit: Mogana Das Murtey and Patchamuthu Ramasamy



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