D. Bacillus cereus – Explanation
The obvious clue in this question is the short incubation period – this points to a diagnosis
ofStaphylococcus aureus or Bacillus cereus. Bacillus cereus infection is often associated with
Chinese restaurants due to the link with rice
There are two recognised types of Bacillus cereus infection. The first type produces a vomiting
illness and has an incubation period of 1-6 hours. The second type produces a diarrhoeal illness with
an incubation period of 6-14 hours.
Gastroenteritis
Gastroenteritis may either occur whilst at home or whilst travelling abroad (travellers’ diarrhoea)
Travellers’ diarrhoea may be defined as at least 3 loose to watery stools in 24 hours with or without
one of more of abdominal cramps, fever, nausea, vomiting or blood in the stool. The most common
cause is Escherichia coli
Another pattern of illness is ‘acute food poisoning’. This describes the sudden onset of nausea,
vomiting and diarrhoea after the ingestion of a toxin. Acute food poisoning is typically caused by
Staphylococcus aureus, Bacillus cereus or Clostridium perfringens.
Stereotypical histories
| Escherichia coli | Common amongst travellers
Watery stools |
| Giardiasis | Prolonged, non-bloody diarrhoea |
| Cholera | Profuse, watery diarrhoea
Severe dehydration resulting in weight loss |
| Shigella | Bloody diarrhoea Vomiting and abdominal pain |
| Staphylococcusaureus | Severe vomiting Short incubation period |
| Campylobacter | A flu-like prodrome is usually followed by crampy abdominal pains, fever and diarrhoea
which may be bloody |
| Bacillus cereus | Two types of illness are seen
|
| Amoebiasis | Gradual onset bloody diarrhoea, abdominal pain and tenderness which may last for several
weeks |
Incubation period
- 1-6 hrs: Staphylococcus aureus, Bacillus cereus*
- 12-48 hrs: Salmonella, Escherichia coli
- 48-72 hrs: Shigella, Campylobacter
- > 7 days: Giardiasis, Amoebiasis
*vomiting subtype, the diarrhoeal illness has an incubation period of 6-14 hours
