Infectious diarrhoea Flashcards
Diarrhoea?
An arbitrary term of increased fluidity and frequency of stool, it is subjective
What is gastro-enteritis?
- Three or more loos stools/day
- Accompanying features
What is dysentery?
Large bowel inflammation, there will be bloody stools
Causes of gastro-enteritis?
- Contamination of food (eg chicken and campylobacter)
- Poor storage of food produce
- Travel-related (Salmonella)
- Person to person spread (Norovirus)
What is the most common cause of gastro-enteritis?
Viral cause - Norovirus, rotavirus, adenovirus
What is the most common cause of bacterial gastro-enteritis?
Campylobacter. 280,000 cases/year
What is a complication of Campylobacter gastroenteritis?
Guillian-Barre Syndrome
What pathogen is most likely to cause a hospital admission with gastro-enteritis?
Salmonella (source = poultry/travel)
What is the most common cause within “food-poisoning”?
Poultry meat (244,000 cases/yr)
How may cases of food poisoning?
500,000/year
What percentage of the population have infectious intestinal disorders per year?
25% of the population
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)
Defences against enteric infections?
- Hygiene
- Stomach acidity
- Normal flora
- Immunity
Clinical features of diarrhoeal illness?
1) Inflammatory = Dysentery
2) Secretory = Watery diarrhoea
3) Mixed picture
Clinical features of non-inflammatory/secretory diarrhoea?
Frequent watery stools with little abdomen pain.
How to treat secretory diarrhoea?
Rehydration is the mainstay of therapy
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
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
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.
What is the most common source of V cholera?
Contaminated water or uncooked food (eg raw shellfish)
Microbiological tests to identify V cholera?
- Gram negative
- Comma shaped with flagellum
- Oxidase positive
- Grows in alkaline media
Microbiological tests to identify E coli?
- Gram negative
- Rod-shaped bacilli
- Catalase positive
- Lactose fermenting
- Encapsulated (antiphagocytic virulence factor)
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
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
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?
4
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
