16. GI infections Flashcards
What toxins can cause GI infections?
- Chemical
- Bacteria
- Viruses
- Protozoa
- Nematodes (Roundworms)
- Cestodes (Tapeworms)
- Trematodes (Flukes)
What are some of the GI defences?
- Sight, smell, memory
- Saliva (bacteriostatic secretions)
- Gastric acid (acidic environment)
- Small intestinal secretions (Bile)
- Colonic mucus
- Anaerobic environment (small bowel, colon)
Define microbiota of the gut.
Refers to the organisms within the gut environment
What are the Benefits of microbiome?
- Harmful bacteria cannot compete for nutrients
- Microbiome produces antimicrobial substances
- Helps to develop newborn’s immune system
- Produce certain nutrients (Vit K)
Which part of the gut is relatively sterile?
Proximal gut is relatively sterile environment
Does the amount of bacteria increase or decrease as you go more distal into GI tract?
increases
What %of faecal mass is bacteria?
20 %
describe the environment of the colon
anaerobic
What do bacteria in the colon produce?
SCFAs (acetate, propionate, butyrate)
What does Butyrate do?
energy source for colonocytes, helps regulate gut environment
What does acetate do?
involved in cholesterol metabolism
What does propionate do?
- helps regulate satiety
What is the general affect of health on the microbiome?
- Obesity- seems to be less diverse population of bacteria
- Inflammatory bowel disease- less diversity
- Microbiome composition affects response to chemotherapy
- Microbiome composition affects insulin response to food
What is Faecal microbiota transplant (FMT)?
Faecal transfer from healthy donors to the sick in order to treat disease
What are the routes of administration of FMT?
• NG/duodenal tubes (unappealing for most patients) - Can be done under anaesthetic
• Upper GI endoscopy
• Colonoscopy
• Transplant can be put in Caecum (allowed to move throughout colon)
- Distributed throughout length of colon
Who are the donors for FMT?
• 10-25 year olds
• Donors do not use (in past 3 months)
- Antibiotics
- Laxatives
- Diet pills
• Do not have GI disease
• Completely screened (inflammatory markers, Hepatitis, HIV)
• Fresh stool to transplantation or storage (1 hour!)
• Stool is centrifuged, filtered and diluted
What questions should be asked about history of diarrhoea?
onset, duration, frequency, consistency (Bristol Stool Chart), mucous/blood
What important parts of history should you ask about?
- History of presenting complaint (diarrhoea, vomiting, pain etc)
- Past medical history
- Travel history (very important)
- Drug history
- Social history
What questions should be asked about history of vomiting?
onset, frequency
What questions should be asked about history of pain?
site, radiation, intermittent/continuous (SQITARS)
What important past medical history should you be aware of in a patients with suspected GI infection?
- Immunodeficiency/immunocompromised state
* Other GI conditions
Why is social history important?
Important to inquire about occupation
- if infection is infectious and patient works in area with lots of people, risk of spreading
- patient should not go back to work until infection has settled
What type of drugs are important to inquire about?
- Recent antibiotics
- Proton pump inhibitors
- Laxatives
- Immunosuppressant medications
What questions are important to ask in travel history?
- Where, when, how long
- Activities
- Food and drink
- Animal contact
- Travel companions & household contacts
What are the different investigations that can be done on a stool sample?
- stool culture
- enzyme immunoassay
- PCR
- Microscopy
Which organisms are tested for via stool cultures?
- E. Coli 0156
- Salmonella
- Shigella
- Campylobacter
Which organisms are tested for via enzyme immunoassay?
- Cryptosporidium
- Giardia
- Clostridioides difficile
Which organisms are tested for via PCR?
- Clostridioides
- Entamoeba histolytica
- Norovirus, rotavirus
- Other bacterial
Which organisms are tested for via Microscopy?
Ova, cysts and parasites
Which organisms typically cause watery diarrhoea?
- Norovirus, rotavirus
- Clostridioides difficile
- Enterotoxigenic E. coli
- Giardia lamblia
- Cryptosporidium parvum
Which organisms typically cause inflammatory diarrhoea?
- Non-typhoidal salmonella
- Campylobacter
- Clostridioides difficile
- Shigella
- E. coli O157
- Entamoeba histolytica
Which gram negative rods can cause bacterial infection of the gut?
- Salmonella
- Campylobacter
- Shigella
- Enterotoxigenic E-coli
Which gram positive rods can cause bacterial infection of the gut?
Clostridium difficile
What are the symptoms of gasteroenteritis caused by salmonella?
Nausea, vomiting and diarrhoea (mostly non-bloody), fever, abdominal cramping
How is salmonella spread?
Spread by ingesting food and water contaminated by salmonella bacteria (symptoms develop 48 hours later)
How is gasteroenteritis due to salmonella treated?
In healthy individuals this is self limiting (2-3 days)
- fluid resuscitation if needd
Describe the pathophysiology of the invasion of salmonella
- Salmonella gain access to enterocytes (endocytosis)
- (rare) Move to submucosa where encounter macrophages
- Macrophages transfer salmonella to reticuloendothelial system where they multiply inside cells
- Causing lymphoid hyperplasia
- Re-enter gut from the liver - possible liver and gallbladder infection
describe the campylobacter bacteria
- Spiral or ‘s’ shaped organism
* Mainly microaerophilic (do not ferment carbs)
What are the possible complications of salmonella and who is at a greater risk of developing them?
- bacteraemia
- endovascular infections,
- abscesses
- osteomyelitis & septic arthritis (more likely in sickle cell disease)
Where is Camplyobacter found?
Found in GI tract of animals especially poultry.
- raw foods cause infection
What is the incubation period and transmission route of Campylobacter?
- Spread to humans via faeco-oral route
- Needs to multiply within host before symptoms appear (food infection- not food poisoning)
- Longer incubation period (1-7 days)
What are the general features of gasteroenteritis due to Campylobacter?
• Fever, abdominal cramping, profuse diarrhoea (can be bloody)
If diarrhoea is bloody in campylobacter, what does it suggest?
invasion infection of colon
How long does gasteroenteritis due to Campylobacter last?
Can lasts days to weeks (generally self limiting)
What is released by campylobacter that causes profuse diarrhoea?
• Releases a cytotoxin (similar to cholera)
What is the treatment for Campylobacter?
- Fluid/electrolyte replacement
* Consider antibiotics if bloody diarrhoea
What does the bacteria shigella cause and who does it commonly affect?
Causes shigellosis which is a dysentery commonly affecting young children < 5 years
What is the transmission route of shigella?
• Transmission: faeco-oral, food and water. Person-to-person transmission can occur due to low infective dose
What are the symptoms of gasteroenteritis due to shigella and what are the reasons behind them?
- Invades large intestine colonocytes, multiplies in cells and invades neighbouring cells
- This kills colonocytes and forms abscesses in the mucosa
- Bloody diarrhoea with mucus and abdominal cramping
What is the treatment of shigella?
Usually resolves in a week
Describe Enterotoxigenic E-coli
• Commensal of the colon but can also be a pathogen
How is Enterotoxigenic E-coli spread?
Spread by faecal oral route or by contaminated food and water
What is enterotoxigenic E-coli a common cause of?
travellers diarrhoea
What is the pathophysiology of gasteroenteritis due to enterotoxigenic E-coli?
- colonise and adhere to enterocytes (produces enterotoxins)
- These cause the hypersecretion of chloride ions from enterocyte to lumen
- Water leaves cells into the gut lumen
How are gram negative bacteria that cause gasteroenteritis spread?
oral route from different sources- faecal, food, water
Which of the gram negative bacteria causing gasteroenteritis cause dairrhoea?
Diarrhoea (all)
• Potentially bloody (Shigella, campylobacter)
• Watery (ETEC, salmonella)
Which of the gram negative bacteria causing gasteroenteritis release toxins?
All
Which of the gram negative bacteria causing gasteroenteritis potentially cause haemolytic uraemic syndrome??
Shigella, campylobacter)
What is haemolytic uraemic syndrome?
A triad of anaemia, thrombocytopaenia and AKI
To which of the gram negative rod infections are antibiotic prescribed?
Antibiotics are carefully prescribed for serious cases (resistance becoming a problem)
order the gram negative rod bacteria into shortest to longest duration
ETEC, salmonella (days), Shigella (week), campylobacter (weeks)
Which one of these gram negative rods is most likely to cause bloody diarrhoea?
shigella
describe clostridium difficile
• Gram positive , anaerobic, spore forming bacillus
how is clostrdium difficile spread?
Minor component of the GI tract but can be transferred via faecal-oral route
why is clostridium difficile gasteroenteritis spread easily?
Spores are very difficult to get rid of from an environment (like a hospital)
What is the major precipitating factor in gastroenteritis caused by C difficile?
antibiotics!
• Following antibiotic therapy C-difficile can colonise gut and release toxins
what are the actions of the toxins released by c difficile?
- Toxins A & B
- A- enterotoxin that results in excessive secretion of water(+ inflammation)
- B- Cytotoxin - kills colonocyte
How does gastroenteritis caused by C difficile present?
- Asymptomatic (most people)
- Varying degrees of diarrhoea (mild to terrible, rarely bloody)
- Abdominal cramping
Which antibiotics particularly lead to c difficile infection?
Most antibiotics can precipitate C- difficile proliferation (especially broad spectrum)
What are some of the complications of c difficile gastroenteritis?
In a few cases (<5%)
• Pseudomembranous colitis
• Toxic megacolon (worst case scenario) - Surgery
What is Pseudomembranous colitis?
- Inflammatory condition
* Elevated yellow plaques join to form a pseudomembrane
What is the Treatment of C. difficile infection?
- Remove offending antibiotic
- Fluid resuscitation
- Metronidazole/Vancomycin
- Probiotics
Which virus is a very common cause for gastroenteritis in the under 5s?
Rotavirus
What type of virus is the rotavirus?
Double stranded RNA virus
How is rotavirus spread?
Spread faecal-oral route (only very small dose required)
Are adults affected by rotavirus and why?
Adults rarely affected (immunity lasts into adulthood)
What are the symptoms of rotavirus gastroenteritis?
- Vomiting with a fever are first symptoms
* Diarrhoea follows (lasting up to a week)
What causes diarrhoea in rotavirus gastroenteritis??
- Chloride secretion
- SGLT1 disruption
- Reduced brush border enzyme function
Describe how chloride secretion can lead to diarrhoea in rotavirus gastroenteritis?
- Creates gradient for the movement of Na into lumen
- Water moves by osmosis following Na
- Diarrhoea
Describe how SGLT1 disruption can lead to diarrhoea in rotavirus gastroenteritis?
- Reduced movement of Na/glucose into enterocyte
- Higher osmotic load in gut
- Water moves by osmosis
Describe how Brush border dysfunction can lead to diarrhoea in rotavirus gastroenteritis?
malabsorption, increased osmotic pressure in lumone, water moves by osmosis into lumen
What is the Most common cause of non bacterial gastroenteritis in the world?
Norovirus
What age does norovirus gastroenteritis affect?
• Can affect any age as there are huge number of strains (don’t develop immunity)
Why is norovirus highly contagious?
- Only requires small dose so highly contagious
* Virus resistant to cleansing
What is the incubation period for norovirus and how long do symptoms last?
Incubation is 1-2 days and symptoms last 1-3 days
Which part of the GI tract does norovirus affect?
Infects the small intestine and damages microvilli (brush border enzymes disruption)
What are the symptoms of norovirus gastroenteritis and explain them?
- Symptoms include vomiting, watery diarrhoea, fever
- Anion secretion, so movement of water into gut lumen
- Vomiting is due to delayed gastric emptying - pressure in stomach increases
what is the treatment for norovirus gastroenteritis?
Treatment is oral rehydration therapy
What are the main pathogens of parasitic gastroenteritis and what are their classifications?
Protozoa that infect the intestinal tract • Cryptosporidium --> Sporozoan - non motile • Giardia lamblia --> Flagellate - motile • Entamoeba --> Amoeba - motile
How is Cryptosporidium spread?
Transmitted by the faecal-oral route but can also be survive and spread via bodies of water (infected by animal faeces)
How does Cryptosporidium cause gastroenteritis?
Disease is caused by the ingestion of an oocyst (a cyst containing the parasite)
• This reproduces inside the epithelial cells of the distal small intestine
• Oocysts are excreted in faeces to continue cycle
What are the symptoms of gastroenteritis due to Cryptosporidium?
Produces watery diarrhoea that is normally self limiting
• Malabsorption (brush border enzymes affected)
• Chloride secretion
What is the treatment for gastroenteritis due to Cryptosporidium?
- Treatment is supportive (fluids)
- Occasionally anti-parasitic treatment in at risk groups
- AIDS- can produce severe symptoms
Who are giardia gastroenteritis more common in?
in children
How id giardia spread?
Spread via faecal-oral route with water supplies often affected (in developing countries)
What are the symptoms of giardia gastroenteritis?
• Most infections are asymptomatic • If symptomatic (appear after 10+ days incubation period) • Diarrhoea • Abdominal cramping • Can last up to 6 weeks Common cause of persistent diarrhoea
Describe the two stages of the life cycle of giardia
- Cyst is ingested
• Stomach acid/ pancreatic enzymes release parasite from cyst
• which then multiplies in small intestine- incubation 1-2 weeks
• Damages proximal small intestine causing symptoms (diarrhoea)
• Villous atrophy occurs - Parasite then goes back into cyst stage in colon
• Excreted to repeat the cycle
What is the treatment for giardia gastroenteritis?
• Antibiotics and fluid rehydration therapy
What is common post giadia infection?
lactase deficiency is common
• Lactose intolerance
Where is Entamoeba histolytica gastroenteritis common?
Higher prevalence in developing countries
Affects:
• People who have travelled to tropical places that have poor sanitary conditions
• People who live in institutions that have poor sanitary conditions
• Men who have sex with men
What are the symptoms of entamoeba histolytica gastroenteritis?
- Most cases are asymptomatic (80%)
- If symptomatic:
- Diarrhoea
- Liver abscesses (rare)
How is entamoeba histolytica spread?
Transmitted by faecal-oral route (from contaminated food or water)
Describe what happens in entamoeba histolytica gastroenteritis
- Infection follows the ingestion of cysts
- Excystation occurs in colon where trophozoites invade mucosa
- Bloody diarrhoea and inflammatory changes occur (similar to IBD)
- Infection can also spread to liver (abscesses form)
- Cysts then pass out with faeces- infect others
What is the treatment for entamoeba histolytica gastroenteritis?
- Anti-protozoals/metronidazole
* Severe colitis/toxic megacolon may require surgery
What is travellers diarrhoea?
Diarrhoea is the most common symptom of travel related illnesses
• Defined as passing 3 or more loose/watery stools
• +/- fever, abdominal pain
What is the most common cause of traveller’s diarrhoea?
• Enterotoxic Escherichia coli (ETEC) is the most common cause of acute travellers’ diarrhoea globally
What factor reduces the likelihood of a bacterial cause of travellers diarrhoea?
Greater than 14 days of symptoms makes it less likely to be bacterial in cause
How is travellers diarrhoea treated?
Mild/moderate (less than 6 stools/24 hrs)
• Hydration (oral rehydration solutions/ safe water)
• Antidiarrhoeal agents
Severe (more than 6 stools/24 hrs)
• IV fluids (potentially)
• Antibiotics (if appropriate)
What increases the risk of developing travellers diarrhoea?
- Place you are visiting (south and east asia, central America, west and north Africa)
- Dietary exposure (backpacking)
- Less than 6 years, PPIs, Blood group O (shigellosis, cholera
Who are given antibiotics when presenting with traveller’s diarrhoea?
- Antibiotics are only recommended for vulnerable patients (immunosuppressed)
- Halves duration of symptoms (to 1.5 days on average)
