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Phase 2 1. Gastroenterology > Infectious diarrhoea > Flashcards

Infectious diarrhoea Flashcards

1
Q

What is Gastroenteritis?

A

inflammation of the stomach and intestines, typically resulting from bacterial toxins or viral infection and causing vomiting and diarrhoea.

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2
Q

How is diarrhoea defined?

A

 3 or more loose or watery stools per day

 faeces that fits the receptacle it is in

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3
Q

What are the pathological mechanism of diarrhoea?

A
  • toxin mediated
  • damage to intestinal epithelial surface
  • invasion across intestinal epithelial barrier
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4
Q

How can toxins be produced?

A

o Produced prior to consumption (S.aureus, B.cereus)

  • Toxins are liberated onto food by the bacteria before the food is consumed
  • Hallmark = sickness a few hours after eating

o Produced after consumption (C.difficile, E.coli 0157)
- Once consumed, the organism replicates within the gut and produces toxins

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5
Q

How can epithelial damage cause diarrhoea?

A

o Direct toxic effect to cells

o Inflammation of the gut causes diarrhoea = gut tries to evacuate the pathogen

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6
Q

What are the three main symptoms to look for in a patient presenting with diarhoea

A
  • vomiting
  • type of diarrhoea
  • non-intestinal manifestations
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7
Q

What is the significance of vomiting in a patient with diarrhoea

A

(nausea common, vomiting uncommon)

o Sudden onset within 6-12hrs of food ingestion suggests pre-formed toxin (in food)
 S. aureus
 B. cereus - e.g. in contaminated rice

o Viral aetiology
 Norovirus
 Sapovirus

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8
Q

How can diarrhoea be classed?

A

classified according to where the predominant infection is:

  • small intestine
  • large intestine
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9
Q

What are the symptoms associated with small intestine diarrhoea?

A

(digestion and absorption) infection will result in:
o high volume diarrhoea
o a lot of cramping (stretching of small intestine)
o weight loss when chronic (due to impaired nutrient absorption)
o bloating
o wind

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10
Q

What are the symptoms of large intestine diarrhoea?

A 
= (fluid and electrolyte absorption) colitis:
o frequent diarrhoea
o small amounts
o Often contains blood
o Fever
o Painful stool
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11
Q

What are the most common bacterial causes of diarrhoea?

A

 Campylobacter sp – by far the most common bacterial cause of gastroenteritis
 Salmonella sp – battery hens are vaccinated against salmonella, greatly reducing prevalence
 Shigella sp – often seen in travellers
 E. coli (0157: H7)
 Clostridium difficile

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12
Q

What are the most common viral causes of diarrhoea?

A

 Norovirus
 Sapovirus
 Rotavirus – common cause of D&V in children
 Adenoviruses – red eye, vomiting, diarrhoea

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13
Q

What are the most common parasitic causes of diarrhoea?

A

 Cryptosporidium – causes small bowel infection
o Colonises the gut of lambs – common in lambing season (infects water supply from faeces
washout)
 Giardia – travel related
 Entamoeba histolytica – LI infection, travel related
 Cyclospora - travel related (often seen in Mexico)
 Isospora - travel related

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14
Q

What should be enquired during a history of a patient with diarrhoea?

A
  • Food history
  • Onset & nature of symptoms
  • Residence
  • Occupation
  • Travel
  • Pets / hobbies
  • Recent hospitalisation / antibiotics
  • Co-morbidity
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15
Q

What is the use of Faecal leukocytes & occult blood testing?

A

Both a waste of time, not used clinically at all in the UK

(idea is that presence of faecal leukocytes may indicate a colonic or “inflammatory” cause
o Poor sensitivity & specificity
o Not used clinically

Faecal occult blood
o Bacterial cause
Faecal calprotectin
o Protein found in stool that can be elevated with inflammation in the gut
o Can be raised but NOT specific for infection

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16
Q

What is the use of obtaining a stool culture?

A

Necessity of documenting a pathogen
o Self-limiting illness
o Indications for treatment – whether or not to give antibiotics
o Public health implications – limiting spread of infection (e.g. preventing people from handling
food while infected)

Consider microscopy for ova and cysts if parasitic cause is possible
o Travellers
o Epidemiology

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17
Q

What are the disadvantages of stool cultures?

A

Low rate positive stool cultures (1.5-5.6% of patients)
o Viral causes cannot be cultured
o Organisms in the gut are used to very specific environmental conditions, and this is incredibly
difficult to reproduce in the lab
o Campylobacter is very difficult to culture
o Many patients will therefore have a false negative

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18
Q

What is the use of endoscopy in patients with diarrhoea?

A

 Not very useful, as it does not add to diagnosis with infective diarrhoea
 Can indicate colitis, but not the source of infection
 Useful when patient has diarrhoea but no infection  can be used to rule out disorders of the gut, e.g.
UC/Crohn’s with biopsies

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19
Q

How is infectious diarrhoea treated?

A

 Oral rehydration solution – morbidity can result from dehydration
o Small intestinal Na-glucose cotransport remains intact
o Can absorb water if Na & glucose also present (osmotic potential)

 May require IV fluid replacement
o Vomiting

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20
Q

Should antibiotics be given to patients with diarrhoea?

A

 Self-limiting illness – antibiotics are usually not required
 Antibiotics reduce duration of diarrhoea by about 1 day (1.7 v 2.8 days)
o This is not worth the damage antibiotics do to the patient or the risk of antibiotic resistance
 Antibiotics can WORSEN outcome in some illnesses
o E. coli 0157:H7

21
Q

Which patients should receive antibiotics?

A
  • v. ill
  • septic/ evident bacteraemia
  • significant co-morbidity
  • certain causes
22
Q

What cause of diarrhoea should be given antibiotics and what antibiotic should be given?

A

C. difficile associated diarrhoea (metronidazole)

23
Q

What is the use of treating symtpoms of diarrhoea?

A

e.g. Imodium
 Generally not indicated
 Potentially worsens prognosis in bacterial disease but may be safe given with antibiotics for travellers
 Diarrhoea is the body’s way of eliminating the organism
 Slowing this down may prolong the duration of illness

24
Q

In what situations can exclusion diets be helpful?

A

o Could potentially be beneficial in managing C.difficile infection
o Travellers diarrhoea = cutting out lactose helps with giardia infection

25
Q

What is the common cause of Campylobacter diarrhoea?

A

Most common source is chicken

26
Q

What is the pathophysiology of campylobacter diarrhoea?

A 
 Infecting dose of ~9000 organisms
 Sensitive to stomach acidity
o Beware things that reduce stomach acidity, e.g. PPIs =
increase susceptibility to infection
 Attach and invade intestinal epithelial cells
o Small bowel
o Large bowel
o Causes mixed diarrhoea
 Incubation period 3 days (1 to 7 days)
o Depends on infecting dose
27
Q

What are the clinical features of campylobacter diarrhoea?

A 
 Diarrhoea
o Frequent and can be high volume
o Blood in stool common
 Abdominal pain (cramping)
 Often severe
 Nausea common / vomiting rare
 Fever
28
Q

How is campylobacter diarrhoea managed?

A

 Clinical course
o Self-limiting (7 days)
 Antibiotics usually not given, rarely indicated
o High rates of antibiotic resistance
o Can develop resistance to the antibiotic used on treatment

29
Q

What are late complications of campylobacter diarrhoea?

A

o Reactive arthritis

o Guillain-Barre

30
Q

What is the main source of SALMONELLA diarrhoea?

A

 Main source = chicken, reptiles (excrete salmonella on their skin)
 Spreads person-to- person

31
Q

Describe the pathophysiology of salmonella diarrhoea

A

 Numerous serotypes, but generally split into:
o Typhoidal (travellers)
o Non-typhoidal
 Infectious dose ~10,000 organisms
 Interactions with host
o Increased risk with decreased stomach acid (PPIs, H2RA, etc.)
o Increased risk with diminished gut flora
 Invasion of enterocytes with subsequent inflammatory response
o Can cause bacteraemia/systemic infection

32
Q

What are the clinical features of salmonella diarrhoea

A

 Illness within 72 hours of ingestion
 Onset of illness depends on inoculum; higher inoculum  more rapid onset
 Nausea, diarrhoea, abdominal cramps, fever

 Invasive disease
o Bacteraemia in <5%
o Secondary infection (endocarditis, osteomyelitis, mycotic aneurysm)

33
Q

How should salmonella diarrhoea be treated?

A 
 NB: when patients with gastroenteritis are treated with antibiotics its normally because of the fear of
invasive salmonella
 Antibiotics
o Self-limiting (up to 10 days)
o No significant reduction in duration
o Severe disease
34
Q

What are the public health implications of salmonella diarrhoea?

A

Clear implications for food handlers (due to person-person transmission)
o Asymptomatic shedding common & episodic
o Median 5 weeks
o Negative stool cultures (>1)

35
Q

What is the main source of e.coli 0157

A

 Found in beef mince, but also in vegetables (bean sprouts, spinach) because of fertiliser (animal faeces)
 Person-person transmission
 Commonly caught at petting zoos
 Excreted by animals with more than one stomach

36
Q

What is the pathogenesis of e.coli 0157

A 
 Attachment to large bowel
 Shiga toxin production
o Enterocyte death
o Enters systemic circulation
 Infectious load as little as 10 organisms – incredibly infectious
 Sporadic outbreaks
37
Q

What are the clinical features of e coli 0157

A

 Incubation period 3 to 4 days
 Bloody diarrhoea & abdominal tenderness
 Fever is rare
> Haemolytic Uraemic Syndrome

38
Q

What is Haemolytic Uraemic Syndrome?

A

Systemic effect of shiga toxin

Triad of:
o Microangiopathic haemolytic anaemia (formation of fibrin clots in small blood vessels => RBC
sheared open when they pass)
o Acute renal failure (most small blood vessels in the kidney)
o Thrombocytopenia (because platelets used in the clots)

39
Q

What is the incidence of Haemolytic Uraemic Syndrome?

A

Only occurs in up to 9% patients
Tends to come on 5 to 10 days after onset diarrhoea
o Diarrhoea may already have cleared

40
Q

How is Haemolytic Uraemic Syndrome treated?

A 
 50% require dialysis
o Mortality 3 to 5%
o Association with antibiotics
 Poorer outcome with antibiotics
 Management
o Supportive, elimination of toxin (dialysis etc.)
 Prevention is key
o Strict infection control for healthcare workers
o Screening of contacts
o Appropriate butchering of meat
o Public health measures in outbreaks
41
Q

What are the risk factors for clostridium difficile infection?

A
  • antibiotic exposure
  • older age (>65 - ?PPI use)
  • hospitalisation

Elderly are at higher risk because gut microbiota decreases with age

42
Q

Describe the pathogenesis of clostridium difficile infection?

A

Destruction of gut microbiota allows colonisation by other bacteria => toxin production

43
Q

What are the symptoms of clostridium difficile infection?

A

 Loose stool & colic
 Fever
 Leukocytosis – because it is toxin-mediated
 Protein losing enteropathy – any condition of the GI tract that results in a net loss of protein from the body (e.g. damage to the gut wall)
 Pseudomembranous colitis – masses of puss on surface of colon

44
Q

How is C diff detected?

A

Toxin detection via:

  • tissue culture assay (no longer commonly used)
  • c. diff antigen/ c. diff toxin

first test for antigen, then test for toxin

45
Q

How is c. diff treated?

A

 Stop causative antibiotics if possible (or at least narrow spectrum)
o Allows normal gut flora to grow back
 Metronidazole / Vancomycin
 Faecal transplant - recolonise with normal flora
o 96% cure rate

46
Q

Describe norovirus

A

Norovirus most common cause of epidemics
o Tends to cause outbreaks within institutions (hospitals, care homes, nurseries, etc.)
o Can lead to hospital ward closure

Occur in all months with peak in winter

47
Q

How is norovirus transmitted?

A

o Faecal oral route
o Infectious dose 10 – 100 viruses
o Very stable organism (can survive up to 60°C, bleach, and utterly resistant to alcohol gel)
 Must wash hands with soap and water, physically wash the virus off

48
Q

What are the clinical features of norovirus?

A

o Acute explosive diarrhoea and vomiting
o Causes illness within 24 – 48 hours
o No lasting immunity

Phase 2 1. Gastroenterology (20 decks)

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