GI Infection

Question 1

Define gastroenteritis

Answer 1

rapid onset diarrhoeal illness, lasting <2 weeks with diarrhoea (loose or unformed stool) ≥3/day or ≥200g of stool which is either viral or bacterial in aetiology

Question 2

Small vs large bowel diarrhoea

Answer 2

o Small bowel diarrhoea = watery, crampy abdominal pain, bloating and gas; inflammatory cells rare

o Large bowel diarrhoea = small volume, painful, occur with blood/mucous; inflammatory cells common

Question 3

Risk factors for GE

Answer 3

o Food borne

o Exposure-related
 Outbreak situation (>2 cases of common food source or exposure)
 Travel history (exposure to poor settings and water facilities)
 Occupational exposure / Health-care related exposure (recent ABx  c. diff)
 Animal contacts (pets, farms, zoos)
 Reptile contact (specifically)
 Institution/childcare facility

o	Host-related 
	Young children and elderly
	Immunosuppressed patients
	MSM
	Anal-genital, oral-anal, or digital-anal contact
	Haemochromatosis or haemoglobinopathy

Question 4

MOA of secretory diarrhoea

Answer 4

o Cholera toxin:
 Subunit production
 cAMP opens Cl- channels at the apical membrane of the enterocytes causing an efflux of Cl- to lumen with loss of water and electrolytes  profoundly dehydrated

o Superantigens:
 Superantigens bind directly to TCRs and MHC molecules; outside the peptide binding site: there is massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response)  secretory diarrhoea

Question 5

Incubation and duration of staph

Answer 5

Incubation 1-4 hrs

24-48 hrs duration

Question 6

Incubation and duration of norovirus

Answer 6

24-48 hr incubation

Lasts 48-72 hrs

Question 7

Inc, duration and spread of E coli

Answer 7

1-3 days
Lasts 2-3 days
Spreads via focally contaminated water or food

Question 8

Campylobacter inc, duration, exposure

Answer 8

1-3 days
Lasts 5-14 days
Poultry, unpasteurised milk and meat

Question 9

Diagnosis of GI infections

Answer 9

• Stools testing – cultures or independent methods (i.e. multiplex molecular PCR)
• Enteric fever – blood and stool tested by culturing and independent testing methods (BM, duodenal fluid and urine)
• Parasites – stools for microscopy and culture (inc. ova cysts and parasites)

Question 10

Inflammatory vs enteric diarrhoea

Answer 10

o Inflammatory (exudative) diarrhoea- mucosa is damaged leading to release into stool

o Enteric fever: interstitial inflammation- causing fever

Question 11

How is Staph aureus spread and treated

Answer 11

Can spread from skin lesions onto food

Treatment is clinically supportive

Question 12

How is Bacillus cereus spread, gram stain and Tx

Answer 12

 Spores germinate in reheated fried rice (heat-stable emetic toxin – not destroyed by reheating)
 Gram +ve rod-spores
Self limiting, watery

Question 13

Clostridida botulinum source, symptoms and Tx

Answer 13

• Source: canned or vacuum-packed food (honey in infants)
• Blocks ACh release from peripheral nerve synapses: paralysis
• Treatment with antitoxin

Question 14

Clostridum perfringens source and symptoms

Answer 14

• Source: reheated food (meat)

* Watery diarrhoea, cramps, vomiting lasting 24hrs

Question 15

Clostridum difficile toxins

Answer 15

o Toxin A = enterotoxin = inflammation

o Toxin B = cytotoxin = virulence factor (more dangerous than A)

Question 16

Listeria sources, symptoms and Tx

Answer 16

 Source: refrigerated food (“cold-enhancement”), unpasteurized dairy, vegetables (grows at 4ºC)

 Symptoms: Watery diarrhoea, cramps, headache, fever, little vomiting
• At risk: perinatal infection, immunocompromised patients, elderly (confused)

 Treatment: amoxicillin

Question 17

Types of E coli and what they cause

Answer 17

• ETEC; toxigenic  main cause of traveller’s diarrhoea
• EPEC; pathogenic  infantile diarrhoea
• EIEC; invasive  dysentery
• EHEC; haemorrhagic  O157:H7 EHEC: shiga-like verocytotoxin causes HUS

• Avoid antibiotics

Question 18

Salmonella types and they disease manifestations

Answer 18

o	S. typhi 	
	Typhoid (enteric) fever
•	Bacteraemia
slow onset, fever and constipation
•	Blood cultures are positive      
•	Treatment: ceftriaxone

o	S. enteritidis
	Enterocolitis
•	Transmitted from poultry, eggs, meat
•	Bacteraemia infrequent, no fever 
•	Self-limited non-bloody diarrhoea, usually no treatment (

Question 19

Symptoms and Tx of shigella

Answer 19

• Dysentery
o Invading cells of mucosa of distal ileum and colon
o Producing enterotoxin (Shiga toxin)

• Avoid antibiotics

Question 20

Vibrios types and manifestation of disease

Answer 20

 Vibrio cholerae
• Faeco-oral transmission inc. shellfish, oysters, shrimp
• Causes massive diarrhoea (rice water stool) without inflammatory cells
• Treat the losses: electrolyte replacement and fluids

 Vibrio parahaemolyticus
• Ingestion of raw or undercooked seafood (i.e. oysters)
• Self-limited for 3 days
• Treat with doxycycline

 Vibrio vulnificus
• Cellulitis in shellfish handlers and fatal septicaemia with D+V in HIV patients
• Treat with doxycycline

Question 21

Camplylobacter symptoms and Tx

Answer 21

 Symptoms: Watery, foul smelling diarrhoea, bloody stool, fever and severe abdominal pain  treat with erythromycin or cipro if in the first 4-5days

Question 22

Entamoeba histolytica characteristics, symptoms and Tx

Answer 22

4 nuclei
Dysentery, flatulence, tenesmus
Metronidazole and paromomycin in luminal disease

Question 23

Giardia lambila characteristics, Sx and Tx

Answer 23

 Trophozoite “pear shaped”; 2 nuclei
Foul smelling non-bloody diarrhoea, cramps, flatulence, no fever
 Treatment: metronidazole

Question 24

Cryptosporidium parvum characteristics, Sx and Tx

Answer 24

 Severe diarrhoea in the immunocompromised (can cause outbreaks)
 Oocysts seen in stool by modified Kinyoun acid fast stain
 Treatment: reconstitution of immune system. Self-limiting

Question 25

Why is Norovirus easily spread

Answer 25

 Low ID load (18-1000 viral particles)
 Environmental resilience (0-60 degrees)
 No long-term immunity