Infectious diarrhoea Flashcards by Callum Hill

Diarrhoea?

An arbitrary term of increased fluidity and frequency of stool, it is subjective

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What is gastro-enteritis?

Three or more loos stools/day

- Accompanying features

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What is dysentery?

Large bowel inflammation, there will be bloody stools

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Causes of gastro-enteritis?

Contamination of food (eg chicken and campylobacter)
Poor storage of food produce
Travel-related (Salmonella)
Person to person spread (Norovirus)

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What is the most common cause of gastro-enteritis?

Viral cause - Norovirus, rotavirus, adenovirus

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What is the most common cause of bacterial gastro-enteritis?

Campylobacter. 280,000 cases/year

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What is a complication of Campylobacter gastroenteritis?

Guillian-Barre Syndrome

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What pathogen is most likely to cause a hospital admission with gastro-enteritis?

Salmonella (source = poultry/travel)

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What is the most common cause within “food-poisoning”?

Poultry meat (244,000 cases/yr)

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How may cases of food poisoning?

500,000/year

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What percentage of the population have infectious intestinal disorders per year?

25% of the population

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What form of Escherichia coli is commonly associated with diarrhoea?

1) EHEC - Most common is Enterohaemorrhagic E. coli O157:H7 (undercooked meats)

2) EIEC - Invasive
3) ETEC - Toxigenic (Travellers’ diarrhoea)
4) EPEC (Paediatrics)

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Defences against enteric infections?

Hygiene
Stomach acidity
Normal flora
Immunity

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Clinical features of diarrhoeal illness?

1) Inflammatory = Dysentery
2) Secretory = Watery diarrhoea
3) Mixed picture

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Clinical features of non-inflammatory/secretory diarrhoea?

Frequent watery stools with little abdomen pain.

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How to treat secretory diarrhoea?

Rehydration is the mainstay of therapy

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Common causes of watery diarrhoea?

V cholera
Enterotoxigenic E. coli = Travellers diarrhoea, heat stable (cGMP) and heat labile (cAMP) toxins
Viruses - Adenovirus, norovirus, rotavirus
Protozoa

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Common causes of watery diarrhoea?

V cholera
Enterotoxigenic E. coli = Travellers diarrhoea, heat stable (cGMP) and heat labile (cAMP) toxins
Viruses - Adenovirus, norovirus, rotavirus
Protozoa

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Mechanism of action in cholera?

Enterotoxin permanently activates Gs leading to an increase in cAMP by adenylate cyclase.

cAMP acts on the chloride channel leading to increased loss of chloride and consequently increased osmolality in the lumen of the GI tract. Water loss occurs as a direct result.

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What is the most common source of V cholera?

Contaminated water or uncooked food (eg raw shellfish)

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Microbiological tests to identify V cholera?

Gram negative
Comma shaped with flagellum
Oxidase positive
Grows in alkaline media

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Microbiological tests to identify E coli?

Gram negative
Rod-shaped bacilli
Catalase positive
Lactose fermenting
Encapsulated (antiphagocytic virulence factor)

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Action of heat-labile toxin in E coli?

Over activates adenylate cyclase leads to a rise in cAMP and activation of chloride channels.

Cl is secreted and thus water efflux

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Action of heat-stable toxin in E coli?

Over activates guanylate cyclase leads to a rise in cGMP. Decreased resorption of NaCl –> Decreased water resorption

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What do pink colonies on MacConkey agar represent?

Fermentation of lactose

How does E coli breakdown lactose?

Produces beta-galactosidase which breaks lactose down into glucose and galactose

Best initial therapy for water diarrhoea?

Rehydration therapy

Clinical features of inflammatory diarrhoea?

- Inflammatory toxin damage or mucosal destruction. - Pain and fever - Dysentery

How to assess a patient with gastro-enteritis?

- Symptoms - Duration - Risks (Food poisoning, recent travel, contact) - Assess hydration (Postural BP, skin turgor, pulse) - Features of inflammation (Faecal leukocytes or lactoferrin/blood)

What electrolyte imbalances occur in diarrhoea?

Gross loss of sodium (80-100 mmol Na) leads to hyponatraemia Gross loss of potassium (40-80 mmol/L in stools)

What investigations are there in diarrhoea?

- Stool culture - Blood culture - Renal function - Blood count - Neutrophilia and haemolysis - Abdominal X-ray, if abdomen distended, tender

Differential diagnosis within diarrhoea?

- Inflammatory bowel disease - Spurious diarrhoea secondary to constipation - Carcinoma - Sepsis

If there is diarrhoea with absence of pain/tenderness, as well as no blood or mucus in the stools what should you consider?

Sepsis

How should you treat gastro-entertitis?

1st line = Rehydration, Iv saline versus oral rehydration solution (Salt/sugar) 2nd line = Abx

What is the incubation period of campylobacter?

7 days

What complications of campylobacter infection are there?

- Guillain-Barre Syndrome | - Reactive arthritis

Is there abdominal pain with campylobacter?

Yes severe

Is the diarrhoea watery or bloody with campylobacter?

Bloody

How should you culture for campylobacter?

Gram negative Oxidase positive Grows at 42oC

What are the sources of campylobacter?

Chickens, contaminated milk and puppies

Campylobacter isolated cases or outbreaks?

Isolated

After exposure to salmonella how long until onset of symptoms?

<48 hrs

What percentage of salmonella have positive blood cultures?

<5%

What are the complications of salmonella?

- Typhoid fever (S typhi) - Gallstones - Post-infectious irritable bowel is common

Is a high or low infectious dose (ID50) required in salmonella?

High

How to culture salmonella?

- Gram negative rods - Lactose negative - Oxidase Negative

Most common isolates of salmonella?

- Salmonella enteritidis | - Salmonella typhimurium

What is interesting about S typhi and S paratyphi?

They both cause enteric fever, typhoid and parathyroid, and not gastroenteritis

What is the main risk of E.coli 0157?

HUS = Haemolytic-uraemic syndrome

What characterises Haemolytic-uraemic syndrome?

- Renal failure - Haemolytic anaemia - Thrombocytopenia

How do you treat E. coli?

Abx are not requited, supportive rehydration therapy

How is E. coli 0157 spread?

Contaminated meat or person to person

What toxin is there is E. coli 0157?

Shiga/verocyto toxin

How does HUS occur?

1) Shiga toxin binds to globotriaosylceramide 2) Platelet activation 3) Micro-angiopathy 4) Attaches to endothelial, glomerular, tubule and mesangial cells

Does shigella occur in isolation or outbreaks?

Outbreaks

How many species of shigella are there?

Which form of E. coli is easily distinguishable from "ordinary" E. coli?

E. coli 0157

Food poisoning outbreaks occasional causes?

- Staph aureus (Toxin) - Bacillus cereus (Re-fried rice) - Clostridium perfringens (Toxins)

What bacteria is linked to re-fried rice food poisoning?

Bacillus cereus

When should Abx be given in gastroenteritis?

- Immunocomprimised - Severe sepsis - Invasive infection - Valvular heart disease - Chronic illness - Diabetes Not indicated in a healthy person with non-invasive infection

When should Abx be given in a previously healthy person with gastroenteritis?

- Invasive infection - Sepsis - Valvular heart disease

What causes Clostridium difficile diarrhoea?

Usually secondary to Abx use (4 C Abxs) or PPIs

What is a complication of Clostridium difficile infection?

Pseudomembranous colitis

What toxin(s) is involved in Clostridium difficile infection?

A = Enterotoxin - Binds to brush border and alters fluid secretion B = Cytotoxin - Disrupts cytoskeleton via actin depolymerisation (Inflammatory)

How is C difficile diagnosed?

Often history is sufficient however either of the toxins can be identified in the stool by antigen detection or PCR

How is C difficile treated?

1) Metronidazole 2) Oral vancomycin For recurrent cases: 1) Fidaxomicin 2) Faecal microbiota transplant 3) Surgery

What Abx can cause C difficile?

The 4 C's: 1) Cephalosporins 2) Co-amoxiclav 3) Clindamycin 4) Clarithromycin Broad spectrum Abs (Eg ampicillin)

How can C difficile be prevented?

- Reduce use of broad spectrum and 4 C Abx - Antimicrobial management team - Isolate symptomatic patient - Wash hands between patients

How do we treat C difficile?

1) Stop Abx 2) Follow treatment algorithm: - Oral metronidazole if no severity markers - Oral vancomycin if 2 or more severity markers

Common protozoa causes of diarrhoea?

- Giardia lamblia | - Cryptosporidium

What is the source of Giardia lamblia?

Contaminated water (Cysts)

How do we treat Giardia lamblia?

Metronidazole

What can be seen on stool microscopy with Giardia lamblia?

Cysts

How does Giardia lamblia infection present?

- Diarrhoea, with fatty stools - Malabsorption - Failure to thrive

How do you diagnose Giardia lamblia infection?

- Multi-nucleated trophozoites or cysts in stool - Antigen detection - Duodenal biopsy (Vegetative form)

Who is likely to be infected with cryptosporidium?

Immunocomprimised (AIDs)

How is cryptosporidium transmitted?

Water contaminated with animal faeces (Oocysts)

How is cryptosporidium diagnosed?

- Oocysts on acid-fast stain | - Antigen detection

How is cryptosporidium treated?

1) Prevention - Filter water supply | 2) Nitrazoxanide

If someone is confirmed to have a cryptosporidium infection what would you want to do next?

Test as to why they may be immunocompromised (AIDs?)

What is an example of an imported parasite that causes diarrhoea, what type of diarrhoea?

Entamoeba histolytica = Bloody (amoebic dysentry)

What is a long term complication of Entamoeba histolytica?

Amoebic liver abscess (Anchovy paste)

How can we test for Entamoeba histolytica?

- Serology - Trophozoites (with engulfed RBCs) or cysts with up to 4 nuclei in stool - Entamoeba fats - Erythrocytes - Antigen detection

How do we treat Entamoeba histolytica?

1) Metronidazole 2) Paromomycin 3) Iodoquinol for asymptomatic cyst passers

What is the most common infantile cause of viral diarrhoea?

Rotavirus

Which season is rotaviral diarrhoea most common?

Winter

How does rotavirus cause diarrhoea?

Villous destruction with atrophy leads to decreased absorption of Na and loss of K

How can we treat rotavirus?

- Supportive, usually self-resolving | - Prevention - Vaccination of all infants

What strains of the adenovirus can cause diarrhoea?

40/41

How can we diagnose rotaviral diarrhoea?

Antigen detection

What type of virus is the rotavirus?

Segmented dsRNA (reovirus)

What is a common cause of viral diarrhoea outbreaks?

Noroviruses - Commonly leads to ward closures with both staff and patients affected

How can you diagnose norovirus?

PCR

Infectious diarrhoea Flashcards

(93 cards)