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Outline how a consumed pathogen can cause disease
- Intoxication: The toxin of an organism is ingested, with or without the live organism
- Infection: Disease is due to microbe ingestion, which colonise the GI tract any may invade
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What are the criteria for diarrhoea? What is its significance?
- Abnormal frequeny and/or fluidity of stool (~3+ daily)
- Usually indicates small bowel disease
- Causes fluid and electrolyte loss
- Severity can vary from self limiting to fatal, depending on pathogen's virulence and host's immunity
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What is dysentery? What are its clinical features?
- An inflammatory disorder of the large bowel, causing blood and pus in the faeces
- Pain, fever and abdominal cramps
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What aspects of a clinical history should be explored when suspecting a IID?
- Vomiting or diarrhoea? Any blood?
- Abdominal pain?
- Frequency/nature of symptoms
- Onset speed
- Travel/food/contact history (e.g. ill friend or recent BBQ)
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Outline the methods used to diagnose a suspected IID
- History: Discussed in another question
- Examination: Abdominal features/fever/dehydration
- Laboratory: Cultures
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What different media can be used to minimise culture contamination by normal GI flora?
- Enrichment: Media beneficial to the suspected pathogen
- Selective: Media suppresses normal flora
- Differential: Media has a chemical affected by a suspected pathogen's biochemical processes, causing colour change (e.g. non-lactose fermenters or haemolytic strep
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Outline the common treatment of bacterial IIDs
- Majority of mild bacterial GI infections will resolve spontaneously
- Adequate hydration important, especially when V/D
- Antibiotics reserved for severe/prolonged disease, as they may prolong or exacerbate disease and cause resistance
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What bacteria shows in microscopy as curved bacilli?
Campylobacter
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Transmitted by contaminated food, milk or water
Seasonal peaks in May and September
Especially found in poultry
Campylobacter
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What is the pathogenesis of campylobacter?
- Invasion in small and large bowel
- Causes inflammation, ulceration and bleeding
- Bacteraemia can occur by dissemination, usually only in immunocompromised
-
Patient presents with:
- Bloody diarrhoea
- Cramping abdominal pain
- Fever
- Lasts up to 3 weeks
Campylobacter
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How is campylobacter treated?
- IV fluids
- If severe/persistent disease, clarithromycin
- If invasive, quinolone or aminoglycosides
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List the common gram negative IIDs
- Campylobacter
- H.Pylori
- E.Coli
- Salmonella
- Shigella
- Vibrio cholerae
- Yersinia entercolitica
- CHESS VY
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List the common gram positive IIDs
- Bacillus
- Listeria
- Aureus
- Clostridium
- BLAC
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How is salmonella spread? What is its pathogenesis?
- Large animal reservoir creates contaminated food, causing outbreaks. Also waterbourne or sometimes horizontal
- Epithelial invasion of distal small intestine = inflammation. Bacteraemia in immunocompromised.
-
Patient presents with:
- Watery diarrhoea
- Vomiting
- Fever in later stages.
- Lasts 2-7 days
Salmonella
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How is salmonella treated?
- IV fluids
- Antibiotics used in invasive/metastatic infections
- Beta lactams, quinolones and aminoglycosides used
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How is shigella transmitted?
- Humans the only reservoir of S.Dysenteriae; spread by faecal-oral.
- Low infectious dose
- Does not persist in the environment or in food.
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What is the pathophysiology of shigella?
- Organisms colonises mucosal epithelium of terminal ileum and colon
- Exotoxin produced = epithelial damage and renal failure (haemolytic uraemic syndrome)
-
Patient presents with :
- Watery diarrhoea which becomes bloody.
- Marked cramping abdominal pain
- Fever
- Lasts 2-3 days
Shigella
-
How is shigella treated?
- IV fluids
- In H-U syndrome or in the infirm, 3rd generation cephalosporins are used.
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What bacteria shows up in microscopy as comma shaped bacilli?
Vibrio cholerae
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How is V.Cholerae transmitted?
- Persists in fresh water, spread by sewage contamination of food/water
- Human-only faecal-oral spread
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What is the pathophysiology of V.Cholerae?
- Flagellae and mucinase used to penetrate intestinal mucous
- Attaches to receptors
- Exotoxin production causes increased electrolyte and fluid loss
- Hypokalaemia, metabolic acidosis (from hyperchloraemia), hypovolaemia and cardiac failure
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Patient presents with frequent, profuse, non-bloody, watery diarrhoea.
- Vibrio Cholerae
- Diarrhoeal bacillus cereus (with cramping pain)
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How is V.Cholerae treated?
- Immediate oral or IV rehydration
- Tetracyclines can shorten shedding duration, but little effect on severity.
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Describe EPEC
- Aetiology
- Pathophysiology
- Clinical features
- Found in infants/children and travellers
- Adherence causes a lesion, disrupting microvilli of intestine = electrolyte loss
- Watery diarrhoea, abdominal pain, vomiting and fever
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Describe ETEC
- Aetiology
- Pathophysiology
- Clinical features
- Infants/children. Major cause of travellers diarrhoea
- Plasmid toxins released
- Watery diarrhoea, abdominal pain and vomiting. No fever
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Describe EHEC
- Aetiology
- Pathophysiology
- Clinical features
- Worldwide outbreaks. Contaminated food, water, dairy or faecal oral
- EPEC-lesion, but also shiga-like toxins released
- Bloody diarrhoea, abdominal pain, vomiting, no fever. HUS = thrombocytopenia, renal failure, anaemia
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Describe EIEC
- Aetiology
- Pathophysiology
- Clinical features
- Poor hygeine/sanitation. Also foodbourne
- Endocytosis into large intestine mucosa = cell lysis = inflammation, necrosis and ulceration
- Bloody diarrhoea, cramping, vomiting, fever
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What bacteria is the cause of 'fried rice syndrome'? Explain this name and list its clinical features
- "Emetic" bacillus cereus
- Bacteria spores persist through initial boiling, then rice left to cool. Spores germinate, multiply and produce heat-stable toxin. After frying, consumption causes near immediate illness.
- Profuse vomiting, abdominal cramps, watery diarrhoea.
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Outline the transmission and clinical features of listeria monocytogenes
- Associated with contaminated foods, especially unpasteurised dairy, pate, cooked meats, smoked fish. Can multiply at 4 celcius
- 3 week incubation, with flu like symptoms usually ignored and so clinically presents as severe systemic infection (e.g. septicaemia or meningitis)
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What is the treatment for an H. Pylori infection?
- Proton pump inhibitor
- Clarithromycin
- Amoxicillin (or Metronidazole in hypersensitive)
-
Outline the pathophysiology of a staph aureus GI infection
- 50% of strains produce an exotoxin; acid resistant and heat stable.
- Bacteria multiply and produce toxin at room temperature
- Incubation period from 15 mins to 6 hours
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What virus is the commonest cause of life-threatening diarrhoea in young babies?
Rotavirus
-
Child presents with viral gastroenteritis, with worse vomiting and diarrhoea than expected. Recent history of outbreak in family/daycare
Rotavirus
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Child presents with cervical lymphadenopathy, watery diarrhoea and fever/vomiting
Respiratory type adenovirus
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What is the most common cause of non-bacterial gastroenteritis?
Norovirus
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What virus normally reappears yearly? When does the outbreak normally occur?
- Norovirus
- January, but also September-November
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