Diarrhoea - Clinical and Laboratory Aspects

Question 1

What is the definition of diarrhoea?

Answer 1

Fluidity and frequency

Question 2

What is the definition of gastro-enteritis?

Answer 2

Three or more loose stools a day
Accompanying features

Question 3

What is the definition of dysentery?

Answer 3

Large bowel inflammation and bloody stools

Question 4

How can a person get gastro-enteritis?

Answer 4

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

Question 5

What is the commonest bacterial pathogen causing gastro-enteritis?

Answer 5

Campylobacter

Question 6

What are the trends in food poisoning?

Answer 6

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

Question 7

What are some defences against enteric infections?

Answer 7

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

Question 8

What are the clinical features of diarrhoeal illness?

Answer 8

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

Question 9

What is the features of non-inflammatory diarrhoeal illness?

Answer 9

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

Question 10

How is non-inflammatory diarrhoeal illness secretory toxin mediated?

Answer 10

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

Question 11

What are the features of inflammatory diarrhoeal illness?

Answer 11

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

Question 12

How is a patient assessed?

Answer 12

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

Question 13

Describe fluid and electrolyte losses?

Answer 13

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

Question 14

What investigations are needed?

Answer 14

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

Question 15

What are some differential diagnosis for diarrhoeal illness?

Answer 15

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

Question 16

What is the treatment for gastro-enteritis?

Answer 16

Rehydration - oral with salt/sugar solution or IV saline

Question 17

Describe campylobacter gastro-enteritis

Answer 17

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

Question 18

Describe salmonella gastroenteritis

Answer 18

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

Question 19

Describe E. coli O157

Answer 19

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

Question 20

What can the toxin in E. coli O157 cause?

Answer 20

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

Question 21

What is haemolytic-uraemic syndrome characterised by?

Answer 21

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

Question 22

What are occasional causes of food poisoning outbreaks?

Answer 22

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

Question 23

When are antibiotics indicated in gastro-enteritis?

Answer 23

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

Question 24

Describe routine bacterial culture

Answer 24

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

Question 25

Describe a routine bacterial culture of campylobacter

Answer 25

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

Question 26

Describe a routine bacterial culture of salmonella

Answer 26

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

Question 27

What are the commonest salmonella infections in the UK?

Answer 27

Salmonella enteritidis and typhimurium Many isolated imported from abroad

Question 28

What do S.typhi and S.parathypi cause?

Answer 28

Enteric fever and not gastro-enteritis

Question 29

What are other bacteria can cause diarrhoeal illness?

Answer 29

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

Question 30

Explain C. difficile diarrhoea

Answer 30

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

Question 31

What is the treatment for C. difficile diarrhoea?

Answer 31

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

Question 32

What is the prevention for CDI?

Answer 32

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

Question 33

What is the management for CDI?

Answer 33

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

Question 34

Describe parasitology

Answer 34

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

Question 35

Describe protozoa

Answer 35

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

Question 36

How is protazoa infection treated?

Answer 36

Metronidazole

Question 37

Describe cryptosporidium parvum

Answer 37

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

Question 38

Describe imported parasites - protozoa

Answer 38

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

Question 39

What is used to treat Entamoeba histolytica?

Answer 39

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

Question 40

Explain rotavirus diarrhoea

Answer 40

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

Question 41

Describe norovirus - viral diarrhoea

Answer 41

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

Question 42

How is norovirus diagnosed?

Answer 42

PCR Strict infection control measures needed