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Infection Systems > Lecture 1: Infectious Diarrhoea > Flashcards

Lecture 1: Infectious Diarrhoea Flashcards

1
Q

what is dysentry?

A

large bowel inflammation, bloody stools

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2
Q

what ways can a person get gastro-enteritis?

A
  • contamination of foodstuffs: intensively farmed chicken and campylobacter
  • poor storage of produce: bacterial proliferation at room temp.
  • travel-related infections e.g. salmonella
  • person to person spread e.g. norovirus
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3
Q

what pathogens are the most common cause of gastroenteritis?

A
  • viruses are most common cause
  • campylobacter is the most common bacterial pathogen
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4
Q

what is the most common pathogen causing hospital admissions with food poisoning?

A

salmonella

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5
Q

list the defences against enteric infections

A
  • hygiene
  • stomach acidity: antacids and infection
  • normal gut flora: C.diff diarrhoea
  • immunity: HIV + salmonella
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6
Q

what are the different types of diarrhoea?

A
  • non-inflammatory/secretory
  • inflammatory
  • mixed picture
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7
Q

features of non-inflammatory/secretory diarrhoea

what causes it, how does it present, whats the treatment

A
  • toxin-mediated usually e.g. cholera and E.coli
  • watery stools, rapid dehydration, relatively little abdo pain
  • rehydration mainstay of treatment
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8
Q

features of inflammatory diarrhoea

what causes it, how does it present, whats the treatment

A
  • bacterial infection usually e.g. shigella dysentery
  • abdo pain, bloody stools, systemic upset
  • rehydration and (sometimes) antimicrobials required
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9
Q

what organism typically causes diarrhoea with a mixed-picture i.e. non-inflammatory (secretory) and -inflammatory?

A

C.difficile

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10
Q

which organsims commonly cause non-inflammatory diarrhoea?

A
  • cholera
  • E.coli
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11
Q

how does cholera cause diarrhoea?

A
  • increased cAMP results in loss of Cl- from cells along with Na and K.
  • osmotic effect leads to massive loss of water from the gut.
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12
Q

how would we assess a patient with diarrhoeal illness?

A
  • inquire about their symptoms and duration
  • assess risk of food posioning: dietary, contact, travel history
  • assess hydration: postural BP, skin turgor, pulse
  • are there features on inflammation? fever, raised WCC
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13
Q

describe the fluid and electrolyte losses due to diarrhoeal illness

A
  • can be severe with secretory diarrhoea: 1-7L fluid per day containing 80-100 mmol Na
  • hyponatraemia due to sodium loss with fluid replacement by hypotonic solutions
  • hypokalaemia due to K loss in stool (40-80mmol/l of K in stools)
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14
Q

diarrhoeal illness investigations

A
  • stool culture +/- molecular or Ag testing
  • blood culture
  • renal function
  • blood count: neutrophilia, haemolysis (E.coli O157)
  • abdo x-ray/CT if abdomen distended, tender
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15
Q

features of campylobacter gastroenteritis

A
  • C.jejuni principle pathogen
  • incubation up to 7 days
  • infection clears within 3 weeks
  • severe abdo pain =/- colitic picture
  • rarely invasive < 1%
  • post-infective sequelae: Guillaine-Barre syndrome, reactive arthritis
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16
Q

which two species of campylobacter cause the most infections?

A

C.jejuni (90%)
C.coli (9%)

17
Q

sources of Campylobacter infection

A
  • chickens
  • contaminated milk
  • puppies
18
Q

del

A
19
Q

Features of E.coli O157:H7

A
  • enterohaemorrhagic E.coli
  • cattle reservoir
  • excretion over three weeks after symptoms
  • produce a shiga-like toxin (SLT)
  • 5-9 days between onset of diarrhoea and haemolytic uremic syndrome (HUS)
  • HUS largely a complication in children and elderly
20
Q

features of Shigella infection

A
  • largely a disease of childhood/travel
  • HUS and seizures may complicate
  • widespread quinolone against shigellosis in developing world leading to resistance
  • different serotypes hamper development of a universal vaccine
21
Q

features of Traveller’s diarrhoea

A
  • enterotoxigenic E.coli, campylobacter and shigella account for 80% of tourist infections (Nepal)
  • about 1/3 travellers develop a bout of diarrhoea
  • usually lasts < 1 week but persistent diarrhoea (> 30 days) in 1-3%
  • significant shortening by antibiotics
22
Q

features of viral gastro-enteritis

A
  • rotavirus is most common viral enteropath
  • > 800,000 deaths in children under 5y
  • faecal-oral transmission
  • infects mature enterocytes of villous body and tip with cell death and lactose intolerance.
23
Q

list some intestinal parasites

A
  • Cryptosporidiosis
  • Giardia
  • entamoeba histolytica
24
Q

gastroenteritis diagnostic requirements

A
  • 3+ stools in 24 hours plus at least one of fever, vomiting, pain, blood/mucus stools
25
Q

features of Cryptosporidiosis

A
  • water-borne outbreaks
  • 3-6% diarrhoea in developed countries
  • cattle the principle reservoir
  • oocysts seen on microscopy
  • self-limiting, but often protracted illness, in non-compromised patients
26
Q

features of Giardia

A
  • present in surface water
  • asymptomatic cyst carriers
  • treatment by metronidazole, tinidazole
27
Q

features of Entamoeba histolytica

A
  • microscopy only 50% sensitive
  • may mimic ulcerative colitis
  • treat symptomatic disease with 10/7 metronidazole and furamide for cyst carriage
28
Q

what % of patients given antimicrobials get diarrhoea?

A

5-10%

29
Q

C.difficile is present in what percentage of antibiotic associated diarrhoea (AAD)? AND WHY?

A

10-15%
overgrowth of C.diff and production of toxins A > enterotoxin and B > cytotoxin

30
Q

antibiotic associated diarrhoea (AAD) treatment

A
  • metronidazole (up to 6% resistant, poor stool concn.)
  • vancomycin (cost and drug resistance in gut flora)
  • teicoplanin/fusidic acid/cholestyramine
  • surgery
31
Q

commonest salmonella isolates in the UK

A
  • salmonella enteriditis
  • salmonella typhimurium
32
Q

HUS is characterised by

A
  • renal failure
  • haemolytic anaemia
  • thrombocytopenia
33
Q

list some occasional causes of food poisoning outbreaks

A
  • Staph aureus (toxin)
  • Bacillus cereus (re-fried rice)
  • Clostridium perfringens (undercooked meat/cooked food left out - toxin accumulates in spore formation)
34
Q

when are antibiotics indicated for gastroenteritis

A
  • immunocompromised
  • severe sepsis or invasive infection
  • chronic illness e.g. malignancy
  • not indicated for healthy hapteint with non-invasive infection
35
Q

treatment for C.diff diarrhoea

A
  • metronidazole (if no severity markers)
  • oral vancomycin (if 2 or more severity markers)
  • fidaxomicin (new and expensive)
  • stool transplants
  • surgery may be required
36
Q

how can C.diff infection be prevented?

A
  • reduction in broad spectrum antibiotics prescribing
  • avoid 4Cs- cephalosporins, co-amoxiclave, clindamycin, ciprofloxacin
  • antimicrobial management team and local antibiotic policy
  • isolate symptomatic patients
  • wash hands between patients - contaxt precautions
  • cleaning environment
37
Q

how is norovirus diagnosed?

A

PCR

38
Q

list the bacterial species that are routinely sought in stool specimens

A
  • campylobacter
  • salmonella
  • shigella
  • e.coli O157
  • cholera (under specific circumstances)

Infection Systems (13 decks)

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