GI Infections

Question 1

Staph aureus infection

Answer 1

• Spreads from hands of poultry workers

ONSET WITHIN 6H

• Presents with watery, non-bloody vomiting and diarrhoea lasting 24h

5 C’s of S. aureus:

• Cocci
• Clusters
• Catalase +ve
• Coagulase +ve
• Clusters (yellow clusters form on blood agar)

Question 2

Bacillus cereus infection

Answer 2

• Associated with reheating fried rice
• ONLY 4 HOURS INCUBATION !
• Spore-producing bacteria
• Produces 2 toxins:

Heat-stable emetic toxin
- Causes symptoms (vomiting) when food is not reheated properly

Heat-labile diarrhoea toxin
- Causes symptoms when food is not cooked to a high enough temperature

Symptoms resolve in 24h but B. cereus can sometimes cause cerebral abscesses

Question 3

Clostridium botulinum

Answer 3

• Associated with tinned food and vacuum-packed food
• Honey should not be given to infants <1y due to risk of infection
• Inactivated by cooking
• Causes paralysis
• Manage with antidote

Question 4

Clostridium difficile

Answer 4

• Associated with antibiotic use, thought to be HAI
• Causes pseudomembranous colitis
• Tx with mentronidazole ± vancomycin and stop other Abx where possible.

4 C’s - Culprits of C. diff

• Cephalosporins
• Co-amoxiclav
• Clindamycin
• Ciprofloxacin

Question 5

Clostridium perfringens

Answer 5

• Associated with not cooking food properly
• <24h incubation
• Watery diarrhoea and cramps lasting 24h
• Superantigen acts on the collon but not in small bowel

Question 6

Listeria monocytogenes

Answer 6

• Associated with refrigerated food especially non-pasteurised milk
• Febrile gastroenteritis with watery diarrhoea
• Babies are susceptible
• Tx with ampicillin

Listeria monocytogenes is:

• beta-haemolytic
• Aesculin +ve
• Tumbling mobility

Question 7

E. coli

Answer 7

2 Enterotoxins:

• Heat labile toxin - acts on adenylyl cyclase and CAMP
• Heat stable toxin - acts on guanylate cyclase

Different subtypes:

• EPEC - Pathogenic, infantile diarrhoea
• EIEC - Invasive, dysentery
• ETEC - Toxinogenic, travellers
• EHEC - haemorrhagic - o157 is the shiga-like verotoxin that causes HUS

12-48 INCUBATION

Mx - supportive care and avoid Abx

Question 8

Salmonella - overview

Answer 8

• Gram negative
• Non-lactose fermenters

12-48H INCUBATION

• Recurrent Salmonella infections can occur in association with reptiles as pets

Question 9

Salmonella enteritidis

Answer 9

• From poultry, eggs and meat
• Binds to epithelium and subepithelium in the jejunum and ileum but not in the large bowel
• Causes watery, non-bloody diarrhoea
• Blood culture -ve but stool sample +ve
• Mx - none needed

Question 10

Salmonella typhoides (Typhoid enteric fever)

Answer 10

• Multiplies in Peyer’s patches and spreads through reticuloendothelial system
• Slow onset fever and CONSTIPATON
• Blood culture +ve
• Causes splenomegaly, rose spots, bradycardia, leukopenia, haemorrhage, shock
• mx with ceftriaxone

Question 11

Salmonella antigens

Answer 11

• Cell wall O
• Flagellar H
• Capsular IV

Question 12

Shigella

Answer 12

• Non-lactose fermenter and non-hydrogen sulphide producer
• Produces Shiga toxin which invades the mucosa of distal ileum and colon

48 - 72H INCUBATION

• Causes DYSENTERY
• Usually self-limiting, supportive tx only
• CIprofloxacin can be used if needed

Question 13

Vibrio cholerae

Answer 13

• Comma shaped
• Found in water contaminated with human faeces e.g. shellfish
• There is colonisation of the small bowel and RICE WATER STOOL
• Supportive tx

Question 14

Vibrios haemolyticus

Answer 14

• Raw seafood/sushi
• Self-limiting, lasts 3 days
• Only grows on salty agar - (seawater is salty)
• Supportive care

Question 15

Vibrio vulnificus

Answer 15

• Causes cellulitis in shellfish handlers
• In HIV patients, can cause severe sepsis and D&V
• Tx with doxycycline

Question 16

Campylobacter

Answer 16

• Transmitted from uncooked food and water, esp unpasterurised milk
• Oxidase positive and motile

48-72H INCUBATION

• Prodromal headache and fever followed by watery, foul smelling, bloody diarrhoea and cramps
• Fever
• Tx with ciprofloxacin if first 4-5 days
• Can cause GBS, reactive arthritis

Question 17

Yersinia enterolitica

Answer 17

• Non lactose fermenter
• Cold enrichment - prefers cold environments
• Spread when food is contaminated with faeces from domesticated/farm animals
• Enterocolitis and mesenteric adenitis
• Necrotising granuloma
• Arthritis, erythema nodosum, reactive arthritis

Question 18

Entamoeba histolytica

Answer 18

• Motile trophozite in diarrhoea
• 4 nuclei
• Cysts ingested, trophozoites settle in the ileum and then colonise caecum and colon

> 7 DAYS INCUBATION!

• FLASK SHAPED ULCER
• Can cause liver abscess (RUQ pain)
• MSM
• Tx with metronidazole, paromycin for luminal disease

Question 19

Giardia lamblia

Answer 19

• PEAR SHAPED trophozoite
• Malabsorption of protein and fat
• Travellers, hikers, institutionalised, MSM

> 7 DAYS INCUBATION!

• Cramps, foul-smelling non-blood diarrhoea, no fever (unlike Campylobacter)
• ELISA string test
• Tx - metronidazole

Question 20

Cryptosporidium parvum

Answer 20

• Swimming pools
• Infects jejunum
• Oocytes seen on Kinyoun acid-fast stain of the stool sample
• Self-limitins, no tx

Question 21

Norovirus

Answer 21

• Predominant strain in GII.2
• Vomiting
• No long-term immunity

Question 22

Rotavirus

Answer 22

• 2x exposure confers life-long immunity
• Mostly affects children <6y
• Secretory diarrhoea with no inflammation

Question 23

Adenovirus

Answer 23

• Types 40 and 41 cause non-bloody diarrhoea in children <2y