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systems: infection ab > Infectious Diarrhoea > Flashcards

Infectious Diarrhoea Flashcards

1
Q

How is diarrhoea defined?

A
  • Subjective

- By fluidity and frequency

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2
Q

How is gastro-enteritis defined?

A
  • Objective

- Three or more loose stools/day with accompanying features

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3
Q

How is dysentery defied?

A
  • Obvious

- Large bowel inflammation with bloody stools

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4
Q

Describe the Bristol stool chart.

A
  • Type 1: separate hard lumps
  • Type 2: sausage shaped but lumpy
  • Type 3: sausage with cracks on the surface
  • Type 4: smooth and soft sausage shaped
  • Type 5: soft blobs with clear cut edges
  • Type 6: fluffy pieces with ragged edges
  • Type 7: watery, entirely liquid
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5
Q

What can cause gastro-enteritis?

A
  • Contamination of foodstuffs (chicken and campylobacter)
  • Poor storage of produce (bacterial proliferation at room temperature)
  • Travel-related infections (salmonella)
  • Person to person spread (particularly viruses such as norovirus)
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6
Q

What is the commonest cause of infectious diarrhoea?

A
  • Viruses

- The commonest bacterial pathogen is campylobacter

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7
Q

What is the most common foodborne pathogen?

A

Campylobacter

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8
Q

What pathogen is responsible for the most hospital admissions each year?

A

Salmonella

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9
Q

Give 3 examples of isolated pathogens found in Scotland.

A
  • Campylobacter
  • Salmonella
  • E.coli O157
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10
Q

What defences are there against enteric infections?

A
  • Good hygiene
  • Stomach acid
  • Normal gut flora
  • Immune system
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11
Q

How can diarrhoeal illness present?

A
  • Non-inflammatory or secretory such as cholera
  • Inflammatory such as shigella dysentery
  • Mixed picture such as C. difficile
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12
Q

How does non-inflammatory diarrhoea present?

A

Frequent watery stools with little abdominal pain

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13
Q

How is non-inflammatory diarrhoea mediated?

A
  • It is secretory toxin-mediated
  • Cholera increases cAMP levels and Cl secretion (loss), increasing osmotic pressure
  • Enterotoxigenic E.coli (traveller’s diarrhoea)
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14
Q

What is the mainstay of therapy for non-inflammatory diarrhoea?

A

Rehydration

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15
Q

How does inflammatory diarrhoea present?

A
  • Inflammatory toxin damage and mucosal destruction
  • Pain and fever
  • Bacterial infection, amoebic dysentery
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16
Q

How is inflammatory diarrhoea treated?

A

Antimicrobials may be appropriate but rehydration alone is often sufficient

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17
Q

How should a patient presenting with diarrhoea be assessed?

A
  • Symptoms and their duration (i,e, >2/52 unlikely to be infective gastro-enteritis)
  • Could it be food poisoning? (diet, contact, travel history)
  • Assess hydration status (postural BP, skin turgor, pulse)
  • Are there features of inflammation? (SIRS) (fever, raised WCC)
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18
Q

What potential fluid and electrolyte loss with diarrhoea?

A
  • Fluid loss can be severe 1-7 litres
  • Hyponatraemia due to sodium loss with fluid replacement by hypotonic solutions
  • Hypokalaemia due to K loss in stool
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19
Q

What investigations should be carried out for diarrhoea?

A

-Stool culture
-Renal function
Blood count (neutrophilia, haemolysis)
-Abdominal x-ray if the abdomen is distended and tender

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20
Q

What is the differential diagnosis for diarrhoea?

A
  • IBD
  • Spurious diarrhoea
  • Carcinoma
  • Sepsis outside of the gut
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21
Q

What is the treatment for gastro-enteritis?

A

Rehydration

  • Oral with salt/sugar solution
  • IV saline
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22
Q

How does campylobacter gastroenteritis present?

A

-Up to 7 days incubation so dietary history may be unreliable
-Stools negative within 6 weeks
-Abdominal pain can be severe
-<1% invasive
Post-infection sequelae can occur

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23
Q

What post infection sequelae can occur with campylobacter gastroenteritis?

A
  • Guillain barre-syndrome

- Reactive arthritis

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24
Q

Why does it take 3 days for a routine bacterial culture?

A
  • Difficult to find pathogen in the midst of complex normal flora
  • Selective and enrichment methods of culture necessary - variety of media and incubation conditions
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25
Q

What campylobacter species are found on routine culture in gastroenteritis?

A
  • C. jejuni

- C. coli

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26
Q

What is the commonest cause of bacterial food poisoning in the UK?

A

Campylobacter

27
Q

How is campylobacter transmitted?

A

Through chickens, contaminated milk and puppies

28
Q

Why are specialised culture conditions required for campylobacter?

A
  • Really fastidious organism

- Needs a bit of oxygen but too much is toxic

29
Q

How does salmonella gastroenteritis present?

A
  • Symptom onset usually <48 hrs after exposure
  • Diarrhoea usually lasts <10 days
  • <5% positive blood cultures
  • 20% patients still have positive stools at 20/52 (pronlonged carriage may be associated with gallstones)
  • Post-infectious irritable bowel is common
30
Q

What are the features of routine bacterial salmonella culture?

A
  • Screened out as lactose non-fermenters - then antigen and biochemical tests
  • Thousands (!) of species with individual names
  • Genetically most are serotypes of the same species (Salmonella enterica)
  • Traditionally named after place of first isolation
31
Q

What are the commonest salmonella isolates in the UK?

A
  • Salmonella enteritidis

- Salmonella typhinmurium

32
Q

What do S. typhi and S.paratyphi cause?

A

Typhoid and paratyphoid (NOT GASTROENTERITIS)

33
Q

How is E.coli O157 transmitted?

A

Infection from contaminated meat or person-to-person spread (low inoculum)

34
Q

How does E.coli O157 cause illness?

A
  • E. coli O157 produces (verocyto-)toxin
  • E. coli O157 stays in the gut but the toxin gets into the blood
  • Toxin can cause haemolytic-uraemic (HUS) syndrome (haemolytic anaemia and renal failure)
35
Q

What is haemolytic-uraemic syndrome characterised by?

A
  • Renal failure
  • Haemolytic anaemia
  • Thrombocytopenia
36
Q

What is the treatment for haemolytic-uraemic syndrome?

A

Supportive

37
Q

What is E.coli O157 infection characterised by?

A

Typical illness characterise by frequent bloody stools

38
Q

How does haemolytic-uraemic syndrome occur?

A 
-Toxin binds to 
globotriaosylceramide
-Platelet activation stimulated
-Micro-angiopathy results
-Attach to endothelial, glomerular,
tubule and mesangial cells
39
Q

Other than E. coli O157, what other forms cause diarrhoea?

A
  • Enteropathogenic
  • Enterotoxic (traveller’s diarrhoea)
  • Enteroinvasive
40
Q

What bacteria are occasional causes of food poisoning?

A
  • Staph aureus (toxin)
  • Bacillus cereus (re-fried rice)
  • Clostridium perfringens (toxin)
41
Q

When are antibiotics indicated?

A

Indicated in gastroenteritis for

  • Immunocompromised
  • Severe sepsis or -Invasive infection
  • Valvular heart disease
  • Chronic illness
  • Diabetes

Not indicated for healthy patient with non-invasive infection

42
Q

How does Clostridium difficile diarrhoea present?

A
  • Patient usually gives history of previous antibiotic treatment – the “4 C antibiotics”
  • Severity ranges from mild diarrhoea to severe colitis
  • C. Diff produces enterotoxin (A) and cytotoxin (B) (inflammatory)
43
Q

How is C.diff diarrhoea treated?

A
  • Metronidazole
  • Oral vancomycin
  • Fidaxomicin (new and expensive)
  • Stool transplants
  • Surgery may be required
44
Q

How is CDI prevented?

A
  • Reduction in broad spectrum antibiotic prescribing
  • Avoid 4 Cs – cephalosporins, co-amoxiclav, clindamycin, clarithromycin
  • Antimicrobial Management Team (AMT) and local antibiotic policy
  • Isolate symptomatic patients
  • Wash hands between patients
45
Q

How is CDI managed?

A
  • Stop precipitating antibiotic (if possible)
  • Follow published treatment algorithm – oral metronidazole if no severity markers
  • Oral vancomycin if 2 or more severity markers
46
Q

What parasites are implicated in diarrhoea?

A

Protozoa and helminths

47
Q

How is parasitic diarrhoea diagnosed?

A
  • Diagnosis generally by microscopy

- Send stool with request “parasites, cysts and ova please” or P, C and O

48
Q

Give examples of UK parasites.

A
  • Giardia lamblia

- Crytosporidium parvum

49
Q

How is giardia lamblia transmitted?

A

Contaminated water

50
Q

How does giardia lamblia infection present?

A

Diarrhoea, malabsorption and failure to thrive

51
Q

How is giardia lamblia infection diagnosed?

A
  • Vegetative form in duodenal biopsy or “string test”

- Cysts seen on stool microscopy

52
Q

How is giardia lamblia infection treated?

A

Metronidazole

53
Q

How is cryptosporidium parvum transmitted?

A

Contaminated water (animal faeces)

54
Q

How is cryptosporidium parvum diagnosed?

A

Cysts seen on microscopy

55
Q

How is cryptosporidium parvum infection treated?

A

No treatment

56
Q

Give an example of a imported parasites?

A

-Entamoeba histolytica (amoebic dysentery)

57
Q

How is entamoeba histolytica infection diagnosed?

A
  • Vegetative form in symptomatic patient - (“hot stool”)

- Cysts seen in asymptomatic patient

58
Q

What is a possible long term complication of entamoeba histolytica infection?

A

Amoebic liver abscess may be long term complication (“anchovy pus”)

59
Q

How is entamoeba histolytica infection treated?

A

Metronidazole

60
Q

What is a common cause of viral diarrhoea in the under 5s?

A

Rotavirus (commoner in Winter)

61
Q

How is rotavirus diarrhoea diagnosed?

A

Antigen detection

62
Q

What is a common cause of viral diarrhoea outbreaks?

A

Norovirus

63
Q

How is norovirus diagnosed?

A

PCR

64
Q

What measures need to be taken with norovirus?

A
  • Very infectious
  • Ward closures are common
  • Strict infection control measures needed

systems: infection ab (12 decks)

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