93-95. Infectious diarrhoea Flashcards
What is the definition of diarrhoea?
3 or more watery stools per day which fits into the same receptacle it sits in
What are the main 3 pathogenic mechanisms of diarrhoea?
- Toxin mediates
- pre-formed toxin (produced prior to consumption)
- produced after consumption - Damage to intestinal epithelial surface - inflamed mucosa
- Invasion across intestinal epithelial barrier
What is more common in infectious diarrhoea: nausea or vomiting?
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)
What are the main functions of the small intestine and how does this relate to small intestinal diarrhoea? Include clinical features
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
What are the main functions of the large intestine and how does this relate to large intestinal diarrhoea? Include clinical features
Absorption of fluid and electrolytes
Excretion of potassium
Frequent, small volumes, painful stool
Fever and blood are common
What are some of the main bacterial species responsible for diarrhoea?
Shigella Salmonella Campylobacter E. Coli Clostridium difficile
What are some of the main viruses responsible for diarrhoea?
Norovirus
Sapovirus
Rotavirus
Adenovirus
What are some of the parasites responsible for diarrhoea?
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
How would you clinically approach a patient with diarrhoeal illness?
History
Faecal leukocytes/occult blood
Stool examination/culture
Endoscopy
Taking a history is the best guide to potential pathogens. What sort of questions would you ask for a diarrhoeal history?
Food history Residence Travel Occupation Recent hospitalisation/antibiotics Pets/hobbies Occupation Onset and nature of symptoms Comorbidity
What may faecal leukocytes indicate?
Colonic/inflammatory cause
Poor sensitivity and specificity - not used clinically
What would faecal occult blood indicate?
Bacterial cause
Why are stool cultures a necessity for documenting an illness with diarrhoea?
Can determine whether it’s a self-limiting illness
Implications for treatment
Public health implications
If parasitic cause is possible, what should be checked for in microscopy?
Ova and cysts
Parasitic cause usually associated with travel
With relation to fluid and electrolyte balance, how can diarrhoea be treated?
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
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?
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)
What are the general features of campylobacter infection?
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)
What are the clinical features of campylobacter infection?
Diarrhoea - frequent and high volume
- blood in stool common
Severe abdominal pain
Nausea (common)/vomiting (rare)
Fever
How is campylobacter infection managed? What are the potential complications?
Self limiting (7 days) High rate of resistance to antibiotics - can resist during treatment (rarely used)
Guilliain-Barre
Reactive arthritis
What are the general features of salmonella infection? How does it interact with the host?
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
What are the clinical features of salmonella infection?
Illness within 72 hours of infection
Nausea, diarrhoea, abdominal cramps, fever
Is an invasive disease - can cause secondary infection and bacteraemia
How is salmonella infection managed?
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)
What is the pathogenesis of E. Coli infection?
Attachment
Shiga toxin is produced
- leads to enterocyte death
- enters systemic circulation
Infectious load as little as 10 organisms
Sporadic outbreaks
What are the clinical features of E. Coli?
Incubation period 3-4 days
Bloody diarrhoea and abdominal tenderness
Fever is rare
What is haemolytic uraemic syndrome with relation to E. Coli?
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
How is haemolytic uraemic syndrome managed?
What are the preventative measures?
Supportive management
Strict infection control for healthcare workers
Screening of contacts
Appropriate butchering of meat
- Public health measures in outbreaks
What are the risk factors associated with C. diff?
antibiotic exposure
older age >65
Use of PPIs?
Hospitalisation
What is the pathogenesis of C. diff infection?
Reduction in colonisation resistance
Colonic colonisation
Toxin production
What are the signs of C. diff infection?
Loose stool
Fever
Leukocytosis
Protein losing enteropathy
How is C. Diff diagnosed?
Toxin detection by either:
Tissue culture assay
C. diff antigen with/without C. diff toxin
How is diarrhoea associated with C. diff treated?
Stop causative antibiotics if possible (use narrow spectrum instead)
Metronidazole (mild)/Vancomycin (severe)
Recolonise with normal flora
How is norovirus transmitted?
Faeco-oral route Infectious dose 10-100 viruses Very stable (up to 60 degrees, bleach, alcohol gel)
What is the seasonality of the norovirus?
Occurs in all seasons but peaks in winter
What are the clinical features of norovirus?
Acute explosive diarrhoea
24-48 hours
No lasting immunity
