Infectious Diarrhoea Flashcards
How is diarrhoea defined?
- Subjective
- By fluidity and frequency
How is gastro-enteritis defined?
- Objective
- Three or more loose stools/day with accompanying features
How is dysentery defied?
- Obvious
- Large bowel inflammation with bloody stools
Describe the Bristol stool chart.
- 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
What can cause gastro-enteritis?
- 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)
What is the commonest cause of infectious diarrhoea?
- Viruses
- The commonest bacterial pathogen is campylobacter
What is the most common foodborne pathogen?
Campylobacter
What pathogen is responsible for the most hospital admissions each year?
Salmonella
Give 3 examples of isolated pathogens found in Scotland.
- Campylobacter
- Salmonella
- E.coli O157
What defences are there against enteric infections?
- Good hygiene
- Stomach acid
- Normal gut flora
- Immune system
How can diarrhoeal illness present?
- Non-inflammatory or secretory such as cholera
- Inflammatory such as shigella dysentery
- Mixed picture such as C. difficile
How does non-inflammatory diarrhoea present?
Frequent watery stools with little abdominal pain
How is non-inflammatory diarrhoea mediated?
- It is secretory toxin-mediated
- Cholera increases cAMP levels and Cl secretion (loss), increasing osmotic pressure
- Enterotoxigenic E.coli (traveller’s diarrhoea)
What is the mainstay of therapy for non-inflammatory diarrhoea?
Rehydration
How does inflammatory diarrhoea present?
- Inflammatory toxin damage and mucosal destruction
- Pain and fever
- Bacterial infection, amoebic dysentery
How is inflammatory diarrhoea treated?
Antimicrobials may be appropriate but rehydration alone is often sufficient
How should a patient presenting with diarrhoea be assessed?
- 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)
What potential fluid and electrolyte loss with diarrhoea?
- 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
What investigations should be carried out for diarrhoea?
-Stool culture
-Renal function
Blood count (neutrophilia, haemolysis)
-Abdominal x-ray if the abdomen is distended and tender
What is the differential diagnosis for diarrhoea?
- IBD
- Spurious diarrhoea
- Carcinoma
- Sepsis outside of the gut
What is the treatment for gastro-enteritis?
Rehydration
- Oral with salt/sugar solution
- IV saline
How does campylobacter gastroenteritis present?
-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
What post infection sequelae can occur with campylobacter gastroenteritis?
- Guillain barre-syndrome
- Reactive arthritis
Why does it take 3 days for a routine bacterial culture?
- Difficult to find pathogen in the midst of complex normal flora
- Selective and enrichment methods of culture necessary - variety of media and incubation conditions
What campylobacter species are found on routine culture in gastroenteritis?
- C. jejuni
- C. coli
What is the commonest cause of bacterial food poisoning in the UK?
Campylobacter
How is campylobacter transmitted?
Through chickens, contaminated milk and puppies
Why are specialised culture conditions required for campylobacter?
- Really fastidious organism
- Needs a bit of oxygen but too much is toxic
How does salmonella gastroenteritis present?
- 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
What are the features of routine bacterial salmonella culture?
- 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
What are the commonest salmonella isolates in the UK?
- Salmonella enteritidis
- Salmonella typhinmurium
What do S. typhi and S.paratyphi cause?
Typhoid and paratyphoid (NOT GASTROENTERITIS)
How is E.coli O157 transmitted?
Infection from contaminated meat or person-to-person spread (low inoculum)
How does E.coli O157 cause illness?
- 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)
What is haemolytic-uraemic syndrome characterised by?
- Renal failure
- Haemolytic anaemia
- Thrombocytopenia
What is the treatment for haemolytic-uraemic syndrome?
Supportive
What is E.coli O157 infection characterised by?
Typical illness characterise by frequent bloody stools
How does haemolytic-uraemic syndrome occur?
-Toxin binds to globotriaosylceramide -Platelet activation stimulated -Micro-angiopathy results -Attach to endothelial, glomerular, tubule and mesangial cells
Other than E. coli O157, what other forms cause diarrhoea?
- Enteropathogenic
- Enterotoxic (traveller’s diarrhoea)
- Enteroinvasive
What bacteria are occasional causes of food poisoning?
- Staph aureus (toxin)
- Bacillus cereus (re-fried rice)
- Clostridium perfringens (toxin)
When are antibiotics indicated?
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
How does Clostridium difficile diarrhoea present?
- 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)
How is C.diff diarrhoea treated?
- Metronidazole
- Oral vancomycin
- Fidaxomicin (new and expensive)
- Stool transplants
- Surgery may be required
How is CDI prevented?
- 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
How is CDI managed?
- Stop precipitating antibiotic (if possible)
- Follow published treatment algorithm – oral metronidazole if no severity markers
- Oral vancomycin if 2 or more severity markers
What parasites are implicated in diarrhoea?
Protozoa and helminths
How is parasitic diarrhoea diagnosed?
- Diagnosis generally by microscopy
- Send stool with request “parasites, cysts and ova please” or P, C and O
Give examples of UK parasites.
- Giardia lamblia
- Crytosporidium parvum
How is giardia lamblia transmitted?
Contaminated water
How does giardia lamblia infection present?
Diarrhoea, malabsorption and failure to thrive
How is giardia lamblia infection diagnosed?
- Vegetative form in duodenal biopsy or “string test”
- Cysts seen on stool microscopy
How is giardia lamblia infection treated?
Metronidazole
How is cryptosporidium parvum transmitted?
Contaminated water (animal faeces)
How is cryptosporidium parvum diagnosed?
Cysts seen on microscopy
How is cryptosporidium parvum infection treated?
No treatment
Give an example of a imported parasites?
-Entamoeba histolytica (amoebic dysentery)
How is entamoeba histolytica infection diagnosed?
- Vegetative form in symptomatic patient - (“hot stool”)
- Cysts seen in asymptomatic patient
What is a possible long term complication of entamoeba histolytica infection?
Amoebic liver abscess may be long term complication (“anchovy pus”)
How is entamoeba histolytica infection treated?
Metronidazole
What is a common cause of viral diarrhoea in the under 5s?
Rotavirus (commoner in Winter)
How is rotavirus diarrhoea diagnosed?
Antigen detection
What is a common cause of viral diarrhoea outbreaks?
Norovirus
How is norovirus diagnosed?
PCR
What measures need to be taken with norovirus?
- Very infectious
- Ward closures are common
- Strict infection control measures needed
