19. Food Poisoning

Question 1

What questions should be asked when taking a history of food poisoning?

Answer 1

Onset, duration
Travel history, food history
Sick contacts
Medications that cause diarrhoea
Severe: fever, acute abdomen

Question 2

What investigations can be done into food poisoning?

Answer 2

PCR, selective culture and light microscopy for protozoa on stool
Blood cultures if hospitalised

Question 3

Which pathogens produce toxins which cause food poisoning?

Answer 3

Staph aureus
Bacillus sereus
Clostridium

Question 4

How does food become contaminated with staph aureus enterotoxin?

Answer 4

Food handler doesn’t wash hands and food left at room temperature

Question 5

What are the 2 syndromes caused by bacillus cereus?

Answer 5

Type 1: Emetic syndrome (preformed toxin)

Type 2: Diarrhoeal syndrome (toxin produced in small intestine)

Question 6

What food is classically contaminated with preformed bacillus cereus toxin?

Answer 6

Boiled rice

Question 7

What is the aetiology of clostridium perfringens food poisoning?

Answer 7

Classically associated with gravy

Contaminated with heat resistant spores

Question 8

What is the aetiology of clostridium botulinum food poisoning?

Answer 8

Typically canned food contaminated with toxin
Toxin absorbed from GIT into bloodstream
Blocks ACh release

Question 9

What bacteria is the most common cause of food poisoning?

Answer 9

Campylobacter jejuni

Question 10

What is the aetiology of campylobacter food poisoning?

Answer 10

Zoonosis; no person to person spread
Meat carcasses, especially chicken, contaminated with faeces during slaughtering
Increased rates during BBQ season

Question 11

What is the pathogenesis of campylobacter food poisoning?

Answer 11

Adheres to jejunum and ileum

Cytotoxin causes local damage, occasionally haemorrhagic necrosis

Question 12

What complications are associated with campylobacter?

Answer 12

Toxic megacolon
BSI
Guillan Barre

Question 13

What is the gram stain of campylobacter?

Answer 13

Curved gram negative bacillus

Question 14

What are the lab features of campylobacter?

Answer 14

Oxidase positive
Greyish colonies on charcoal agar
Hydrolyses hippurate

Question 15

What is the treatment for campylobacter BSI?

Answer 15

Azithromycin or ciprofloxacin

Question 16

What is the most common serotype of enterohaemorrhagic E.coli?

Answer 16

O147:H7

Question 17

What complication is associated with enterohaemorrhagic E.coli?

Answer 17

Haemolytic uraemic syndrome

Question 18

How is e.coli O157 differentiated from other e.coli?

Answer 18

On a mannitol/sorbitol plate, O157 doesn’t ferment sorbitol

Question 19

What toxins are associated with enterotoxigenic e.coli?

Answer 19

LT and ST toxins

Cause secretion of fluid and electrolytes

Question 20

What infection is caused by enteropathogenic e.coli?

Answer 20

Infants <6 months in developing countries
Causes severe dehydration
Invasion and loss of villi in small intestine

Question 21

How is listeria food poisoning contracted?

Answer 21

Milk products, even refrigerated
Vertical transmission
Animal contact

Question 22

How does listeria evade the immune system?

Answer 22

Survives within macrophages

Question 23

What are the complications of perinatal listeriosis?

Answer 23

Miscarriage
IU death
Premature labour
Neonatal listeriosis

Question 24

What are the lab features of listeria?

Answer 24

Gram positive bacillus

Tumbling motility at 25C

Question 25

What is the treatment for listeria?

Answer 25

High dose amoxicillin and gentamicin

Question 26

What antibiotic is listeria resistant to?

Answer 26

Cephalosporins

Question 27

What parasite can contaminate water?

Answer 27

Cryptosporidium parvum

Question 28

Why are boil water notices given if a water supply is contaminated with cryptosporidium?

Answer 28

Oocytes can survive outside body and can’t be killed with chlorine

Question 29

How is cryptosporidium detected?

Answer 29

Auramine or PCR