Diarrhoea - Clinical and Laboratory Aspects Flashcards
What is the definition of diarrhoea?
Fluidity and frequency
What is the definition of gastro-enteritis?
Three or more loose stools a day
Accompanying features
What is the definition of dysentery?
Large bowel inflammation and bloody stools
How can a person get gastro-enteritis?
Contamination of foodstuffs - intensively farmed chicken and campylobacter
Poor storage of produce
Travel related infections - salmonella
Person to person spread - norovirus
What is the commonest bacterial pathogen causing gastro-enteritis?
Campylobacter
What are the trends in food poisoning?
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
What are some defences against enteric infections?
Hygiene
Stomach acidity - antacids and infection
Normal gut flora - Cl. difficile diarrhoea
Immunity - HIV and salmonella
What are the clinical features of diarrhoeal illness?
Non-inflammatory/ secretory - cholera
Inflammatory - shigella dysentery
Mixed picture - C. difficile
What is the features of non-inflammatory diarrhoeal illness?
Frequent watery stools with little abdomen pain
Rehydration is mainstay of therapy
Secretory toxin-mediated
How is non-inflammatory diarrhoeal illness secretory toxin mediated?
Cholera increases cAMP levels and Cl secretion along with Na and K - causes osmotic effect so loss of water from gut
Enterotoxigenic E. coli
What are the features of inflammatory diarrhoeal illness?
Inflammatory toxin damage and mucosal destruction
Pain and fever
Bacterial infection/ amoebic dysentery
Antimicrobials may be appropriate but rehydration is often sufficient
How is a patient assessed?
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
Describe fluid and electrolyte losses?
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
What investigations are needed?
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
What are some differential diagnosis for diarrhoeal illness?
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
What is the treatment for gastro-enteritis?
Rehydration - oral with salt/sugar solution or IV saline
Describe campylobacter gastro-enteritis
Up to 7 day incubation
Stool negative within 6 weeks
Abdominal pain can be severe
Post invasive sequelae - Guillain Barre syndrome and reactive arthritis
Describe salmonella gastroenteritis
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
Describe E. coli O157
Infection from contaminated meat or person to person spread
Characterised by bloody stools
Stays in gut but toxin gets into blood
Produces Shiga toxin
What can the toxin in E. coli O157 cause?
Haemolytic uraemic syndrome (HUS) - haemolytic anaemia ad renal failure
Toxin stimulates platelet activation and micro-angiopathy results
What is haemolytic-uraemic syndrome characterised by?
Renal failure, haemolytic anaemia and thrombocytopenia
Treatment is supportive and antibiotics not indicated
What are occasional causes of food poisoning outbreaks?
Staph aureus - toxin
Bacillus cereus - re-fried rice
Clostridium perfringens - undercooked meat or cooked meat left out
When are antibiotics indicated in gastro-enteritis?
Immunocompromised
Severe sepsis or invasive infection
Chronic illness - malignancy
Not indicated in healthy patient with non-invasive infection
Describe routine bacterial culture
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
Describe a routine bacterial culture of campylobacter
Specialised culture conditions
2 species cause most infections - C. jejuni and C. coli
From chicken, contaminated milk and puppies
Isolated cases instead of outbreaks
Describe a routine bacterial culture of salmonella
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
What are the commonest salmonella infections in the UK?
Salmonella enteritidis and typhimurium
Many isolated imported from abroad
What do S.typhi and S.parathypi cause?
Enteric fever and not gastro-enteritis
What are other bacteria can cause diarrhoeal illness?
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
Explain C. difficile diarrhoea
Patient usually gives history of previous antibiotic treatment - 4C antibiotics
Severity ranges from mild to severe colitis
Produces enterotoxin A and cytotoxin B
What is the treatment for C. difficile diarrhoea?
Metronidazole
Oral vancomycin, fidaxomicin, stool transplants and surgery may be required
What is the prevention for CDI?
Reduction in broad spectrum antibiotics
Avoid - cephalosporins, co-amoxiclav, clindamycin and ciprofloxacin
Antimicrobial management team
Wash hands and isolate patients
What is the management for CDI?
Stop precipitating antibiotics
Follow published treatment algorithm - oral metronidazole if no severity markers
Oral vancomycin if 2 or more severity markers
Describe parasitology
Protozoa and helminths
Diagnosis by microscopy - send stool request with parasites, cysts and ova please
Describe protozoa
Giardia duodenalis - cysts/ trophozoites
Diarrhoea, gas, malabsorption and failure to thrive
Cysts seen on microscope
Transmitted by direct contact and food contamination with faeces
How is protazoa infection treated?
Metronidazole
Describe cryptosporidium parvum
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
Describe imported parasites - protozoa
Entamoeba histolytica
Trophozoites in symptomatic patient and in asymptomatic then cysts in formed stool
Antibody detection in serum
Intestinal disease
What is used to treat Entamoeba histolytica?
Metronidazole and luminal agent to clear colonisation
Amoebic liver abscess is long term complication
Explain rotavirus diarrhoea
Rotavirus in children under 5
Common in winter
Diagnosis by antigen in stool
Describe norovirus - viral diarrhoea
Small round structured viruses, Norwalk like viruses and winter vomiting disease
Common cause of outbreaks
Hospital, community and cruise ships
Very infection
How is norovirus diagnosed?
PCR
Strict infection control measures needed
