Enteric Infections Flashcards
What bacteria cause diarrhoea/ Gastroenteritis (GE)
bacteria (examples);
- campylobacter (most common)
- salmonella
- shigella
- E.coli
- clostridium difficile
What virus’ cause diarrhoea/ Gastroenteritis (GE)
Norovirus (no.1)
sapovirus
rotavirus
adenovirus
What parasites cause diarrhoea/ Gastroenteritis (GE)
cryptosporidium (very common in UK, especially during lambing season) Giardia Entamoeba histolytica cyclospora isospora
What are the symptoms of enteric infection
- vomiting/nausea (nausea is more common than vomiting)
- Diarrhoea (small + large intestine)
- non intestinal manifestations (Botulism, campylobacter can cause Gullian barre syndrome)
What does vomiting as a symptom suggest regarding the aetiology
ingestion of pre-formed toxin in food
S. aureus, B.cereus
norovirus (viral aetiology)
what is the definition of diarrhoea
3 or more watery/loose stool per day
what type of diarrhoea is produced if there is too fluid and enzyme secretion in the SMALL INTESTINE
large volume watery diarrhoea
cramps, bloating, wind, weight loss due to malabsorption.
fever and blood in stool is rare
what type of diarrhoea is produced if there is absorption of fluid and salt in the LARGE INTESTINE
frequent small volume, painful stool
fever and blood in stool is common
Describe the pathogenic mechanism of diarrhoea
- Toxin mediated
(toxin produced prior to consumption in S.aureus and B.cereus)
(toxin produced after consumption in C.dificile and E.coli) - damage to intestinal epithelial lining
- invasion across the intestinal epithelial barrier (enterocytes)
Describe the investigation of infectious diarrhoea
History (GOOD history is very important)
Stool examination
Endoscopy
What key aspects would be covered in the history taking of a patient
food history
onset and nature of symptoms (small/large stools)
residence- more common in nursing homes
occupation- more risk in sewer/livestock workers
travel history
pets/hobbies- lizards or snakes covered in salmonella
recent hospitalisations
co-morbidity (heart failure or diabetes)
Why are majority of the stools not cultured for examination
because most pathogens are fastidious (only grows when specific nutrients are available)
describe the role of stool examination
low rate of positive stool cultures (1.5-5.6%)
describe the role of endoscopy for GE
rarely needed for GE
used to look for non-infection causes like IBD
However, occasionally the diagnosis of some pathogens requires biopsy like CMV in immunocomprimised
What are the treatments available for GE
Oral rehydration solution
May require i.v fluid replacement if vomiting
Why are antibiotics not that useful to treat GE
- Antibiotics reduce duration of diarrhoea by 1 day (not a significant difference)
- Antibiotics can worsen the outcome in some(E.coli)
- Antibiotic resistance
When should patients be given antibiotics
- very ill patients (sepsis)
- consider if signifcant comorbidity (little reduction in diarrhoea be clinically meaningful)
- certain causes (c.dificile associated diarrhoea- vancomycin/metronidazole)
what is the advice for symptomatic treatment like imodium
Do not use them
describe how campylobacter causes GE
- infecting dose is of 9000 organisms
- sensitive to stomach acidity
- attaches and invades intestinal epithelial cells (small +large intestine)
- incubation period is of 3 days (1-7 days)
incubation period is the time from the moment of exposure to until symptoms of the disease appear
what are the clinical features of campylobacter
- Diarrhoea (frequent and high volume, blood in stool common)
- abdominal pain (often severe)
- nausea is common (vomiting is rare)
- fever
- self limiting (organism that limits its own growth by its actions)
- antibiotics are rarely given (risk of resistance)
What are the late complications of campylobacter
reactive arthritis
Gullain-Barre syndrome
describe how salmonella causes GE
numerous serotypes - typhoidal (causes typhoid fever) - non-typhoidal (causes GE) infectious dose of 10,000 organisms interactions with host - increased risk if decreased stomach acid - increased risk if diminished gut flora invasion of enterocytes with subsequent inflammatory response
what are the clinical features of salmonella
- illness within 72 hrs of ingestion
- nausea, diarrhoea, abdominal cramps, fever
- antibiotics dont reduce duration
- common in food handlers
What are the complications of salmonella
- bacteraemia (bacteria in blood)
- secondary infection (endocarditis, osteomyelitis, mycotic aneurysm)
describe how E.coli causes GE
- attachment
- shiga toxin production (enterocyte death, enters sytemic circulation- can cause problems with kidneys)
- infectious dose of 10 organisms
- sporadic outbreaks
- can catch it from animals that haven’t been butchered properly
what are the clinical features of E.coli
- incubation period is 3-4 days
- bloody diarrhoea and abdominal tenderness
- fever is rare
describe a complication of E.coli
Haemolytic uraemic syndrome
- systemic effect of shiga toxin
triad of:
- microangiopathic haemolytic anaemia (reduces RBC count)
- acute renal failure
- thrombocytopenia (this more than renal failure in older people)
- develops 5-10 days after onset diarrhoea
- 50% require diarrhoea
- low mortality
- avoid antibiotics
what is the management and prevention of E.coli
management- supportive prevention - strict infection control for heath workers - screening of contacts - appropriate butchering of meat - public health measures in outbreaks
what are the risk factors of Clostridioides Difficile infection
- chemotherapy (destroys gut flora)
- antibiotic exposure (broad spectrum destroy gut flora)
- older age (>65 years)
- PPI use (increased risk of colonisation)
- hospitilisation
what are the pathogenesis of Clostridioides Difficile
- decreased colonisation resistance
- colonic colonisation
- toxin production
(ulceration of the gut)
what are the clinical features of Clostridioides Difficile
- loose stool and colic (severe pain in the abdomen, especially seen in babies)
- fever
- leukocytosis (increased WBC in blood)
- protein losing enteropathy
what is the diagnosis of Clostridioides Difficile infection
- presence of organism and toxin in stool
check if CD is present in stool, if it is present then check if it is PRODUCING the toxin- i.e causing diarrhoea
what antibiotics are used for treatment of Clostridioides Difficile
broad spectrum
- vancomycin
- metronidazole
what is the treatment for Clostridioides Difficile
- aim is to recolonise normal flora
- stop causative antibiotics (broad spectrum)
- take narrow spectrum antibiotics
what is the treatment advised for patients with recurrent Clostridioides Difficile
Faecal Transplant
what is the most common viral cause of gastroenteritis
norovirus
present all year round
causes epidemics
describe the transmission of norovirus
- faecal oral route
- infectious dose of 10-100 viruses
- can grow in stable environment (cant grow in bleach, up to 60 C)
- occurs in all seasons (peak in winter)
what are the clinical features of norovirus
acute diarrhoea and vomiting
24-48 hrs
no lasting immunity
(ppl feel like they are dying) LoL
