Bacillus cereus (food poisoning)

Last edited 02/2020

Bacillus cereus is a relatively infrequent cause of food poisoning.

Cause: Bacillus species, mainly Bacillus cereus, which produce toxins (enterotoxins). Gastrointestinal infections also caused by Bacillus subtilis and Bacillus licheniformis

Reservoir:

• Ubiquitous in the environment, including soil
• Contaminated food sources also important route including cereal products, herbs and spices, dried foods, dairy and meat products
• No human or animal reservoirs

Epidemiology:

• Bacillus spp. are found worldwide but reported food poisoning caused by the bacteria is rare due to the high infectious dose required and under-reporting; but known to cause outbreaks associated with contaminated food sources
• Annual numbers of reported B. cereus food poisoning outbreaks in the UK have varied between 1992 and 2013 from 0 to 8, with a large outbreak in 2012 affecting 200 individuals

Transmission:

• Transmission occurs via consumption of contaminated cooked foods subjected to inadequate post-cooking temperature control which has allowed bacterial growth
• Bacillus cereus – mainly rice dishes (e.g. outbreaks of fried rice in Chinese restaurants), also pasta, meat or vegetable dishes and dairy products
• Bacillus subtilis and licheniformis – mainly meat or vegetable with pastry products, cooked meat and poultry products, also bakery products and ethnic meats
• Possible transmission has been linked to organ preservation fluid and contaminated parenteral nutrition
• Person-to-person spread is not documented

Incubation Period:

• Bacillus cereus
• Emetic syndrome - average 2-3 hours (range 1-6) hours
• Diarrhoeal syndrome - 8-12 hours (range 6-24 hours)
• Bacillus subtilis – 10 minutes–4 hours (average 2.5 hours)
• Bacillus licheniformis – 2–14 hours (average 8 hours)

Clinical features:

• Bacillus cereus – 2 clinical syndromes may occur caused by different toxins:
• Emetic syndrome (heat-stable toxin) – nausea and vomiting, abdominal pain with or without diarrhoea. Generally, a mild illness lasting <12 hours
• his is commonly associated with boiled rice in which hardy spores have survived. When the rice is left at room temperature for several hours before frying, it allows the spores to germinate, so producing vegetative bacilli. The bacilli produce toxin.
• Diarrhoeal syndrome (heat-labile toxin) – diarrhoea (which may be profuse and watery) and abdominal pain with or without nausea and vomiting lasting around 24 hours
• This is more commonly associated with ice cream, meat or vegetables
• Bacillus subtilis – nausea, vomiting and diarrhoea
• Bacillus licheniformis – diarrhoea and abdominal pain

Infectivity: Not applicable as no risk of person-to-person spread

Case definition of Bacillus species food poisoing/Bacillus species - any person who meets at least one clinical criterion OR at least one laboratory criterion for Bacillus species food poisoning/ Bacillus species.

Clinical:

• sudden onset of nausea AND vomiting
• abdominal cramps AND diarrhoea

OR

Laboratory:

• isolation of >=10^5 B. cereus organisms per gram or direct detection of B. cereus enterotoxin from epidemiologically implicated food in the setting of a person or persons with diarrhoea or vomiting
• isolation of the organism from the stools of 2 or more ill persons but not from the stools of controls, in an outbreak situation

Food, faeces or vomit may be used to culture the organism.

Treatment is symptomatic.

Reference:

• PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections