93-95. Infectious diarrhoea

Question 1

What is the definition of diarrhoea?

Answer 1

3 or more watery stools per day which fits into the same receptacle it sits in

Question 2

What are the main 3 pathogenic mechanisms of diarrhoea?

Answer 2

1. Toxin mediates
   - pre-formed toxin (produced prior to consumption)
   - produced after consumption
2. Damage to intestinal epithelial surface - inflamed mucosa
3. Invasion across intestinal epithelial barrier

Question 3

What is more common in infectious diarrhoea: nausea or vomiting?

Answer 3

Nausea.
If vomiting is the predominant symptom, it’s usually caused by a virus (e.g. norovirus) or pre-formed toxins (e.g. S. aureus, B cereus)

Question 4

What are the main functions of the small intestine and how does this relate to small intestinal diarrhoea? Include clinical features

Answer 4

Responsible for fluid and enzyme secretion
Nutrient absorbing

Large volume of watery diarrhoea
Cramps, bloating, wind, weight loss

Fever and blood in stool are rare

Question 5

What are the main functions of the large intestine and how does this relate to large intestinal diarrhoea? Include clinical features

Answer 5

Absorption of fluid and electrolytes
Excretion of potassium

Frequent, small volumes, painful stool
Fever and blood are common

Question 6

What are some of the main bacterial species responsible for diarrhoea?

Answer 6

Shigella
Salmonella
Campylobacter
E. Coli
Clostridium difficile

Question 7

What are some of the main viruses responsible for diarrhoea?

Answer 7

Norovirus
Sapovirus
Rotavirus
Adenovirus

Question 8

What are some of the parasites responsible for diarrhoea?

Answer 8

Giardia - small bowel
Cryptosporidium - most common, lives in guts of lambs
Entamoeba histolytica - large intestine, travel related
Cyclospora - avoid salads and fruit salads, eat cooked food
Isospora

Question 9

How would you clinically approach a patient with diarrhoeal illness?

Answer 9

History
Faecal leukocytes/occult blood
Stool examination/culture
Endoscopy

Question 10

Taking a history is the best guide to potential pathogens. What sort of questions would you ask for a diarrhoeal history?

Answer 10

Food history
Residence
Travel
Occupation
Recent hospitalisation/antibiotics
Pets/hobbies
Occupation
Onset and nature of symptoms
Comorbidity

Question 11

What may faecal leukocytes indicate?

Answer 11

Colonic/inflammatory cause

Poor sensitivity and specificity - not used clinically

Question 12

What would faecal occult blood indicate?

Answer 12

Bacterial cause

Question 13

Why are stool cultures a necessity for documenting an illness with diarrhoea?

Answer 13

Can determine whether it’s a self-limiting illness
Implications for treatment
Public health implications

Question 14

If parasitic cause is possible, what should be checked for in microscopy?

Answer 14

Ova and cysts

Parasitic cause usually associated with travel

Question 15

With relation to fluid and electrolyte balance, how can diarrhoea be treated?

Answer 15

Oral rehydration solution

• small intestinal Na-glucose cotransport remains intact
• can absorb water if Na and glucose also present

IV fluid replacement may be required if there is vomiting involved

Question 16

Antibiotics should not be used in all patients as it may only improve diarrhoea by 1 day and can also worsen circumstances in some cases.

Therefore, who should get antibiotics?

Answer 16

Very ill patients (e.g. sepsis)

Those with significant comorbidity (the reduction in diarrhoea is clinically meaningful)

Certain causes e.g. C. diff associated diarrhoea (treated with metronidazole)

Stool cultures take 48-72 hours for result

(Quinolones - broad spectrum antibiotics)

Question 17

What are the general features of campylobacter infection?

Answer 17

Infecting dose of approx 9000 organisms
Sensitive to stomach acidity
Attach and invade intestinal epithelial cells (small and large)
Incubation period of 3 days (1-7 days)

Question 18

What are the clinical features of campylobacter infection?

Answer 18

Diarrhoea - frequent and high volume
- blood in stool common

Severe abdominal pain

Nausea (common)/vomiting (rare)

Fever

Question 19

How is campylobacter infection managed? What are the potential complications?

Answer 19

Self limiting (7 days)
High rate of resistance to antibiotics - can resist during treatment (rarely used)

Guilliain-Barre
Reactive arthritis

Question 20

What are the general features of salmonella infection? How does it interact with the host?

Answer 20

Can be typhoidal or non-typhoidal
Infectious dose approx 10000 organisms
Invasion of enterocytes with subsequent inflammatory response

Increased risk with decreased stomach acid
Increase risk with diminished gut flora

Question 21

What are the clinical features of salmonella infection?

Answer 21

Illness within 72 hours of infection
Nausea, diarrhoea, abdominal cramps, fever

Is an invasive disease - can cause secondary infection and bacteraemia

Question 22

How is salmonella infection managed?

Answer 22

Self limiting (up to 10 days)
Antibiotics only used in severe disease as it doesn't change duration much

N.B. food handlers can be asymptomatic - shedding is common and episodic
Median 5 weeks
Negative stool cultures (>1)

Question 23

What is the pathogenesis of E. Coli infection?

Answer 23

Attachment
Shiga toxin is produced
- leads to enterocyte death
- enters systemic circulation

Infectious load as little as 10 organisms
Sporadic outbreaks

Question 24

What are the clinical features of E. Coli?

Answer 24

Incubation period 3-4 days
Bloody diarrhoea and abdominal tenderness
Fever is rare

Question 25

What is haemolytic uraemic syndrome with relation to E. Coli?

Answer 25

The systemic effect of shiga toxin

Has a triad:

• microangiopathic haemolytic anaemia
• Acute renal failure
• Thrombocytopenia (low platelet count)

Occurs in 9% of patients, 5-10 days after onset diarrhoea
50% require dialysis
3-5% mortality
Associated with antibiotics

Question 26

How is haemolytic uraemic syndrome managed?

What are the preventative measures?

Answer 26

Supportive management

Strict infection control for healthcare workers
Screening of contacts
Appropriate butchering of meat
- Public health measures in outbreaks

Question 27

What are the risk factors associated with C. diff?

Answer 27

antibiotic exposure
older age >65
Use of PPIs?
Hospitalisation

Question 28

What is the pathogenesis of C. diff infection?

Answer 28

Reduction in colonisation resistance
Colonic colonisation
Toxin production

Question 29

What are the signs of C. diff infection?

Answer 29

Loose stool
Fever
Leukocytosis
Protein losing enteropathy

Question 30

How is C. Diff diagnosed?

Answer 30

Toxin detection by either:
Tissue culture assay

C. diff antigen with/without C. diff toxin

Question 31

How is diarrhoea associated with C. diff treated?

Answer 31

Stop causative antibiotics if possible (use narrow spectrum instead)
Metronidazole (mild)/Vancomycin (severe)
Recolonise with normal flora

Question 32

How is norovirus transmitted?

Answer 32

Faeco-oral route
Infectious dose 10-100 viruses
Very stable (up to 60 degrees, bleach, alcohol gel)

Question 33

What is the seasonality of the norovirus?

Answer 33

Occurs in all seasons but peaks in winter

Question 34

What are the clinical features of norovirus?

Answer 34

Acute explosive diarrhoea
24-48 hours
No lasting immunity