Enteric Infection - Infectious Diarrhoea Flashcards
Name three pathogenic mechanisms of an enteric infection.
Toxin mediated
Damage to intestinal epithelial surface
Invasion across intestinal epithelial barrier
Name some bacteria that have a toxin mediated pathogenic mechanism of causing diarrhoea.
- produced prior to consumption
- produced after consumption
Prior - S.aureus and B.cereus
After - C.diff and E.coli
What bacteria and what virus can cause vomiting within 6-12 hours of consuming food?
S.aureus and B.cereus - because if symptoms set in this quick, then the bacteria must be preformed
Norovirus
Describe the diarrhoea most commonly produced when the small intestine is affected.
Large volumes of watery diarrhoea
Causes cramps, bloating, wind and weight gain
Fever and blood in the stool is rare
Describe the diarrhoea most commonly produced when the large intestine is affected.
Frequents, small volumes of painful stool
Fever and blood is common
What are the main causes of bacterial diarrhoea?
- list some less common if you can
S.aureus B.cereus E.coli C.diff Shigella Salmonella Campylobacter sporidium
Vibrio sporidium
C.perfringens
Yersinia
Plesiomonas
What are the main causes of viral diarrhoea?
Norovirus
Rotavirus
Adenovirus
What are the main causes of parasitic bacteria?
Cryptosporidium Giardia Entamoeba histolytica Cyclospora Isospora
What four steps can help diagnose the patient?
History
Stool leukocytes and occult blood
Stool examination and culture
Endoscopy
What must you ask a patient in a diarrhoeal history?
Food history Onset and nature of symptoms Residence Occupation Travel Pets/hobbies Recent hospitalisation/antibiotics Co-morbidity
Why do we look at faecal leukocytes and occult blood when diagnosing a diarrhoeal illness?
The presence of faecal leukocytes may indicate a colonic or ‘inflammatory’ cause
- poor sensitivity and specificity and not used clinically
Faecal occult blood can indicate a bacterial cause
Why do we do a stroll culture when diagnosing a diarrhoeal illness?
Necessary to document a pathogen
- self liming illness
- indicators for treatment
- public health implications
When would you perform a stool microscopy during the diagnosis of a diarrhoeal illness?
Is a parasitic cause is possible - to look for ova and cysts
- check travellers and those whose epidemiology suggests this
Why would you perform an endoscopy when trying to diagnose a diarrhoeal illness?
To look for an alternative cause of the diarrhoea - so when the cause is unknown
- e.g. Inflammatory bowel disease or neoplastic disease
Describe how an oral rehydration solution works.
To stop diarrhoea we need to absorb more salt, in order to drag the water from the intestine, into the body.
To do this people are given a salt and water solution to ingest
It also contains glucose because salt is absorbed better in the presence of glucose - NA-glucose cotransporter
Name two ways in which fluid replacement treatment can be given to someone with diarrhoea.
Oral rehydration therapy
IV fluid
What are the downsides with using antibiotics in some cases?
- can sometimes be self limiting
- reduces durations by only a day
- can worsen E.coli cases
Who should get antibiotics?
Very ill patients - sepsis or evidence of bacteraemia
Those with significant comorbidity
- reducing the duration is clinically meaningful
Certain causes - C.diff associated diarrhoea (metronidazole)
Describe the infectious dose and mechanism of invasion of campylobacter.
Infectious dose - around 9000 organisms
Attach to and invade the intestinal epithelial cells in both the small and large bowel
Incubation period - 3 days
What are the clinical features of a campylobacter infection?
Diarrhoea - frequent, high volume, often with blood
Abdominal pain - often severe
Nausea
Fever
How should a campylobacter infection be managed and why?
It should be left alone
- self limiting (7 days)
- high rates of antibiotic resistance
- develops resistance on treatment
What is the infectious dose of salmonella, and how long does it take to infect the host?
Around 10000 organisms
Illness within 72hrs of ingestion - but the more organisms there are, the more rapid the onset
How does salmonella affect the intestine of the host?
It’s decreases stomach acid (big risk)
Diminishes the gut flora (increased risk)
Invades enterocytes with a subsequent inflammatory response
What are the clinical features of salmonella?
Nausea
Diarrhoea
Abdominal cramps
Fever
In how many cases does salmonella cause bacteraemia?
Less than 5%
What is the pathogenesis and infectious load of E.coli?
Pathogenesis
- attachment
- Shiga toxin production - kills the enterocytes and enters systemic circulation
Infectious load can be as little as 10 organisms - with a 3-4 incubation period
What are the clinical features of an E.coli infection?
Bloody diarrhoea and abdominal tenderness
Fever is rare
E.coli can cause haemolytic uraemic syndrome in 9% of patients. What is this?
Systemic effect of Shiga toxin It causes - microangiopathic haemolytic anaemia - acute renal failure - thrombocytopenia
What is the treatment and mortality rate for haemolytic uraemic syndrome?
50% of patients need dialysis
3-5% mortality rate
How is an E.coli infection treated and prevented?
Supportive management Prevention - infection control fro health care workers - screening of contacts - appropriate butchering of meat - public health measures in outbreaks
What are the risk factors of C.diff associated diarrhoea?
Antibiotic exposure
Being older than 65
PPI use
Hospitalisation
What is the pathogenesis of C.diff associated diarrhoea?
It decreased colonisation resistance
The colon gets colonised
Toxins are produced
What are the clinical features of C.diff associated diarrhoea?
Loose stool and colic
Fever
Leukocytes is
Protein losing enteropathy
How can C.diff associated diarrhoea be diagnosed?
Antigen detection
Toxin detection
What is the treatment for C.diff associated diarrhoea?
Stop causative antibiotics if possible
Metronidazole or vancomycin
Allows recolonisation with normal flora
What is the most common cause of viral gastroenteritis?
Norovirus - the winter vomiting bug
How is Norovirus transmitted and what is its infectious dose?
Faecal-oral route
Infectious dose is 10-100 viruses
What are the clinical features of a Norovirus infection?
Acute explosive diarrhoea and vomiting lasting 24-48 hours
Out of parasitic, viral and bacterial, which is the most common cause of infectious diarrhoea?
Viral
What is the definition of diarrhoea?
3 or more loose or watery stools per day
