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Infection > Diarrhoea - Clinical and Laboratory Aspects > Flashcards

Diarrhoea - Clinical and Laboratory Aspects Flashcards

1
Q

What is the definition of diarrhoea?

A

Fluidity and frequency

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2
Q

What is the definition of gastro-enteritis?

A

Three or more loose stools a day
Accompanying features

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3
Q

What is the definition of dysentery?

A

Large bowel inflammation and bloody stools

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4
Q

How can a person get gastro-enteritis?

A

Contamination of foodstuffs - intensively farmed chicken and campylobacter
Poor storage of produce
Travel related infections - salmonella
Person to person spread - norovirus

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5
Q

What is the commonest bacterial pathogen causing gastro-enteritis?

A

Campylobacter

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6
Q

What are the trends in food poisoning?

A

500000 cases a year from known pathogens
Campylobacter is most common foodborne pathogen
Salmonella causes the most hospital admissions
Poultry meat related to most cases of food poisoning

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7
Q

What are some defences against enteric infections?

A

Hygiene
Stomach acidity - antacids and infection
Normal gut flora - Cl. difficile diarrhoea
Immunity - HIV and salmonella

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8
Q

What are the clinical features of diarrhoeal illness?

A

Non-inflammatory/ secretory - cholera
Inflammatory - shigella dysentery
Mixed picture - C. difficile

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9
Q

What is the features of non-inflammatory diarrhoeal illness?

A

Frequent watery stools with little abdomen pain
Rehydration is mainstay of therapy
Secretory toxin-mediated

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10
Q

How is non-inflammatory diarrhoeal illness secretory toxin mediated?

A

Cholera increases cAMP levels and Cl secretion along with Na and K - causes osmotic effect so loss of water from gut
Enterotoxigenic E. coli

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11
Q

What are the features of inflammatory diarrhoeal illness?

A

Inflammatory toxin damage and mucosal destruction
Pain and fever
Bacterial infection/ amoebic dysentery
Antimicrobials may be appropriate but rehydration is often sufficient

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12
Q

How is a patient assessed?

A

Symptoms and their duration - if more than 2 weeks then less likely to be gastro-enteritis
Risk of food poisoning
Assess hydration - postural BP, skin turgor and pulse
Features of inflammation - fever and raised WCC

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13
Q

Describe fluid and electrolyte losses?

A

Can be severe with secretory diarrhoea - 1-7l a day containing 80-100 Na
Hyponatraemia from sodium loss with replacement with hypotonic solutions
Hypokalaemia due to K loss in stool

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14
Q

What investigations are needed?

A

Stool culture and possible molecular or Ag testing
Blood culture
Renal function
Blood count - neutrophilia and haemolysis
Abdominal X-ray/ CT if tender or distended abdomen

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15
Q

What are some differential diagnosis for diarrhoeal illness?

A

IBD
Spurious diarrhoea - secondary to constipation
Carcinoma
Diarrhoea with fever can occur with sepsis outside the gut - lack of abdo pain and no blood or mucus in stool

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16
Q

What is the treatment for gastro-enteritis?

A

Rehydration - oral with salt/sugar solution or IV saline

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17
Q

Describe campylobacter gastro-enteritis

A

Up to 7 day incubation
Stool negative within 6 weeks
Abdominal pain can be severe
Post invasive sequelae - Guillain Barre syndrome and reactive arthritis

18
Q

Describe salmonella gastroenteritis

A

Symptom onset usually before 48hrs after exposure
Diarrhoea lasts usually less than 10days
Less than 5% positive blood cultures
Post-infectious irritable bowel is common and prolonged carriage may be associated with gallstones

19
Q

Describe E. coli O157

A

Infection from contaminated meat or person to person spread
Characterised by bloody stools
Stays in gut but toxin gets into blood
Produces Shiga toxin

20
Q

What can the toxin in E. coli O157 cause?

A

Haemolytic uraemic syndrome (HUS) - haemolytic anaemia ad renal failure
Toxin stimulates platelet activation and micro-angiopathy results

21
Q

What is haemolytic-uraemic syndrome characterised by?

A

Renal failure, haemolytic anaemia and thrombocytopenia
Treatment is supportive and antibiotics not indicated

22
Q

What are occasional causes of food poisoning outbreaks?

A

Staph aureus - toxin
Bacillus cereus - re-fried rice
Clostridium perfringens - undercooked meat or cooked meat left out

23
Q

When are antibiotics indicated in gastro-enteritis?

A

Immunocompromised
Severe sepsis or invasive infection
Chronic illness - malignancy
Not indicated in healthy patient with non-invasive infection

24
Q

Describe routine bacterial culture

A

Selective and enrichment methods of culture necessary - variety of media and incubation methods
Takes 3 days to complete
Hard to find pathogen in midst of complex normal flora

25
Q

Describe a routine bacterial culture of campylobacter

A

Specialised culture conditions
2 species cause most infections - C. jejuni and C. coli
From chicken, contaminated milk and puppies
Isolated cases instead of outbreaks

26
Q

Describe a routine bacterial culture of salmonella

A

2 species - S. enterica and S. bongori
More than 2500 serotypes with individual names
Screened out in lab as lactose non-fermenters - look alike microscope - then antigen and biochemical tests

27
Q

What are the commonest salmonella infections in the UK?

A

Salmonella enteritidis and typhimurium
Many isolated imported from abroad

28
Q

What do S.typhi and S.parathypi cause?

A

Enteric fever and not gastro-enteritis

29
Q

What are other bacteria can cause diarrhoeal illness?

A

Shigella - children’s nurseries
Several other forms of E.coli can cause diarrhoea - enteroinvasive, enteropathogenic and enterotoxin
Routine diagnosis of E.coli strains are not possible - only E.coli O157

30
Q

Explain C. difficile diarrhoea

A

Patient usually gives history of previous antibiotic treatment - 4C antibiotics
Severity ranges from mild to severe colitis
Produces enterotoxin A and cytotoxin B

31
Q

What is the treatment for C. difficile diarrhoea?

A

Metronidazole
Oral vancomycin, fidaxomicin, stool transplants and surgery may be required

32
Q

What is the prevention for CDI?

A

Reduction in broad spectrum antibiotics
Avoid - cephalosporins, co-amoxiclav, clindamycin and ciprofloxacin
Antimicrobial management team
Wash hands and isolate patients

33
Q

What is the management for CDI?

A

Stop precipitating antibiotics
Follow published treatment algorithm - oral metronidazole if no severity markers
Oral vancomycin if 2 or more severity markers

34
Q

Describe parasitology

A

Protozoa and helminths
Diagnosis by microscopy - send stool request with parasites, cysts and ova please

35
Q

Describe protozoa

A

Giardia duodenalis - cysts/ trophozoites
Diarrhoea, gas, malabsorption and failure to thrive
Cysts seen on microscope
Transmitted by direct contact and food contamination with faeces

36
Q

How is protazoa infection treated?

A

Metronidazole

37
Q

Describe cryptosporidium parvum

A

Carried by more than 150 species of mammals
20 species known to infect people
Diarrhoea, N/V and abdo pain
Infected animals/ faeces
Oocysts seen on microscope
No specific treatment required

38
Q

Describe imported parasites - protozoa

A

Entamoeba histolytica
Trophozoites in symptomatic patient and in asymptomatic then cysts in formed stool
Antibody detection in serum
Intestinal disease

39
Q

What is used to treat Entamoeba histolytica?

A

Metronidazole and luminal agent to clear colonisation
Amoebic liver abscess is long term complication

40
Q

Explain rotavirus diarrhoea

A

Rotavirus in children under 5
Common in winter
Diagnosis by antigen in stool

41
Q

Describe norovirus - viral diarrhoea

A

Small round structured viruses, Norwalk like viruses and winter vomiting disease
Common cause of outbreaks
Hospital, community and cruise ships
Very infection

42
Q

How is norovirus diagnosed?

A

PCR
Strict infection control measures needed

Infection (13 decks)

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