Lecture 15: Enteric Infection Flashcards
What are the 3 most common symptoms of enteric infection?
- Vomiting
- Diarrhoea
- Non-intestinal manifestations e.g. paralysis of the face
What is an enteric infection?
The name given to any disease caused by an intestinal infection
How common is vomiting?
Very rare- nausea (the feeling of sickness) is more common
When vomiting is the predominant symptom what certain aetiologies does the suggest?
- Staphylococcus aureus
- Bacillus cereus
- Norovirus
- Food poisoning
Nausea is a common symptom of ___ gastroenteritis
Infectious gastroenteritis
Define gastroenteritis?
Gastro- means stomach
enteron- means small intestine
inflammation of the stomach and small intestine, typically resulting from bacterial toxins or viral infection.
Gastroenteritis is defined as a diarrheal disease
Describe the mechanism utilised by the toxins in order to survive so they can be ingested in food?
Common in food that is kept warm on hot plates or reheated food.
The bacteria grow on the food and release these toxins into the food. When heated, the bacteria die but many of these toxins a heat-resistant and therefore are still present on the food.
Define diarrhoea?
Diarhhoea is defined as 3 or more loose or watery stools in 24 hours or at least 200 grams of stool per day
The stool must hold the shape of its container i.e. liquid consistency
What are the major differences between small and large bowel associated diarrhoea?
Small intestine:
Cause is usually fluid and enzyme secretion
Signs are large volume of watery diarrhoea
Rare blood or fever
Cramps and bloating due to the distention of the SI
large intestine:
Cause is absorption of fluid and salt
Frequent defecation but small volume (painful stool)
Fever and blood is common
Give examples of pathogens that produce toxins prior to consumption?
Staphylococcus aureus
Bacillus cereus
Give examples of pathogens that produce toxins after consumption?
Clostridium difficle
Escherichia coli (E.coli) 0157 (important to remember the name as E.coli have many strains some good some bad)
What are the 3 major pathogenic mechanisms for gastroenteritis?
- Toxin mediated
- Organisms produce toxins (before prior or after consumption)
- Damage to the intestinal epithelial surface
- Invasion across the intestinal epithelial barrier
Give examples of bacteria that can cause gastroenteritis?
aka bacterial gastroenteritis
Campylobacter (most common)
Salmonella
Shigella
E.coli 0157
Clostridium difficle
Give examples of viruses that can cause gastroenteritis?
aka viral gastroenteritis
Norovirus
Sapovirus
Rotavirus
Adenoviruses
Sapovirus, rotavirus and adenoviruses are common viral infections in which group of patients?
Common cause of illness in children
Less so in adults
Norovirus is a common viral infection in which group of patients?
Adults
Less common in children (while sapovirus, rotavirus and adrenoviruses are common in children)
Give examples of parasites that can cause gastroenteritis?
aka parasitic gastroenteritis
Cryptosporidium
Giardia (found in contaminaed food and water- important take a travel history)
Why is Cryptosporidium infections common in the UK?
Because the cryptosporidium parasite infects both humans and farm animals
More common in spring months (in the lambing season) because if the lamb is infected with this parasite then so will their feces. The parasite gets washed away from the feces and enters surrounding water supply.
Common as well with patient attending farming and lamb petting events
What are the 3 goal stands when assessing a patient with enteric infection?
- 1st is history
- Most important
- Stool examination/ culture
- Difficult since the feces will have numerous organisms present (Due to the microflora of the gut)
- Selective mediums to grow the culture in
- Endoscopy
- Looking for the signs of infection (Remember PRISH- pain, redness, immobility, swelling and heat)
Name some the key aspects when taking a history for a patient with suspected enteric infection? and why
- Food history
- Ingestion of any toxins
- Occupation
- Certain jobs put people at higher risk e.g. live stock workers.
- Travel
- Pets
- Snakes are covered in multiple organisms
- Recent antibiotic use
- Useful to identify Clostridium difficle
- Co-morbidity
- Infection can destabilise chronic illnesses
Describe the pros and cons of stool culture in gastroenteritis?
Cons:
Majority of the time it is not used as by the time the organism is cultured the diarrhoea is gone (usually lasts 48 hours).
Low rate positive stool culture: hard to recreate the bowel environment- therefore many organisms cannot be cultured.
Pros:
Useful to indicate possible treatments and to document the pathogen
What is a more useful technique instead of stool culture for parasites only?
Look at the stool down a microscope.
Can identify eggs if parasite is present
Describe the pros and cons of endoscopy for gastroenteritis?
Rarely used for gastroenteritis
Useful to rule out non-infectious causes e.g. IBD.
Occasionally useful when the diagnosis requires biopsy.
What is the goal stand treatment for gastroenteritis?
Oral rehydration solution to prevent dehydration
Self-limiting: will get better on its own
May require IV fluid replacement if they cannot keep fluids down (i.e. more fluids out than in)
Give an example of an enteric infectious agent that if antibiotics are given it will make the infection worse than better?
E.coli 0157
If you give antibiotics with 0157, the E.coli responds by producing more toxins
Treatment is IV fluid and monitor kidney function
On average, antibiotics use reduces the duration of diarrhoea from __ to __?
Without antibiotics diarrhoea would last aprrox. 2.8 days
With antibiotics around 1.7 days
Reduction by ONE DAY
What are the 3 groups of people that antibiotics may help if they have diarrhoea?
- Very ill patients
- Immunocompromised etc
- Significant comorbidity
- Certain causes
- Clostridium difficle infection
Why are loperamide or other OTC medication not advised with patients with diarrhoea?
When is it appropriate
Diarrhoea is the body’s mechanism to remove toxic pathogens.
Therefore by reducing the diarrhoea, the body is unable to remove the toxins.
Therefore, it increases the length of infection (As it takes the body longer to remove the toxins) and increases the risk of invasion from invasive organisms (as they are staying longer in the intestines)
What is a unique recommendation with patients suffering with Giardia infection?
Recommended to exclude lactose for a period of time
Define the term “infecting dose”?
Infectious dose is the smallest quantity of infectious material that regularly produces infection
A bacteria with a high infectious dose requires lots of the bacteria in order to produce an infection in the host
Is the infectious dose for Campylobacter high or low?
High infectious dose
Why are people taking PPI or other drugs to reduce stomach acid at a higher risk to Campylobacter?
Campylobacter are sensitive to the stomach acid, therefore one of the mechanisms to prevent infection.
People taking PPI are at higher risk as they have a reduction in this preventative mechanism
Name the clinical features for Campylobacter infection?
- Fever
- Diarrhoea
- Frequent and can be high volume
- Blood in stool common
- Abdominal pain
- Nausea is common
- Vomiting is rare
What is the standard treatment for Campylobacteri?
Self-limiting
Lasts approx 7 days
Will get better on its own
When taking a history about an infection, why must you ask if they keep or have recently been in contact with reptiles ?
Reptiles, e.g. snake, have a high level of Salmonella on their skin
Describe the public health measure that has resulted in a large decline in the number of cases of Salmonella?
Factory chickens are being vaccinated against Salmonella, one of the major ways in which Salmonella was transferred to humans
What is the infection dose for Salmonella?
Very high
approx. 10,000 organisms
If you take a higher innoculum of the organisms what happens to the time of onset?
More rapid onset
Salmonella infection you get clinical symptoms after how long?
Illness within 72 hrs ingestion
Which infection is significant in food handlers and why?
Salmonella infection
The median duration of salmonella shedding after intestinal infection is 5 weeks. During this time, hosts are asymptomatic
Define bacteria shedding?
Humans shed bacteria throughout the course of the infection. Shedding can last for several days to several weeks, and people may become temporary carriers for several months or longer.
What is Verocytotoxigenic Escherichia coli (VTEC)?
VTEC is a particular group of the bacterium Escherichia coli. Although most strains of E. coli are harmless and live in the intestines of healthy humans and animals, VTEC strains produce a powerful toxin and can cause severe illness.
Most common member is E.coli 0157
Most common ways in which people get VTEC?
- Direct contact with VTEC-contaminated faecal material, as a result of handling or petting animals e.g. petting zoos.
- Fruit and vegetables can be contaminated if they come in contact with soil, animal faeces or manure which contains VTEC.
What is the infectious dose for E.coli 0157?
Small infectious dose
As little as 10 organisms i.e. highly infectious
Describe the clinical features of E.coli 0157?
- Incubation period 3 to 4 days
- Bloody diarrhoea & abdominal tenderness
- Fever is rare
Discuss Clinical features of gastroenteritis
- Watery, usually nonbloody diarrhea — bloody diarrhea usually means you have a different, more severe infection.
- Abdominal cramps and pain.
- Nausea, vomiting or both.
- Occasional muscle aches or headache.
- Low-grade fever.
Discuss the management of infectious diarrhoea
Self-limiting will get better on its own.
Dehydration required due to the high level of fluid loss
In high risk groups, e.g. children and elderly, antibiotics may be useful but very rare
Describe the pathogenesis of E.coli 0157 infection?
E.coli attach to the gut mucosa.
Starts to produce Shiga toxin
The Shiga toxin induces apotosis of the enterocytes
The Shiga toxin enters the systemic circulation and transferred into endothleial cells causing damage to blood vessels in certain organs including the kidney.
Results in bloody diarrhoea
Describe the pathogenesis of Salmonella?
Salmonella organisms are ingested in food survive passage through the gastric acid barrier and invade the mucosa of the small and large intestine and produce toxins.
The salmonella organisms invade the epithelial cells stimulating the release of proinflammatory cytokines which induce an inflammatory reaction
Describe the pathogenesis of Campylobacter
Initiated by the ingestion of contaminated food or water
The organisms penetrate the gastrointestinal mucus and adhere to the gut enterocytes.
Once adhered can then induce diarrhoea by toxin release
What is the major risk factor for Clostidiodes Difficile infection?
Broad spectrum antibiotic use
Describe the pathogenesis of Clostidiodes Difficle infection?
Results from a disturbance of the normal bacterial flora of the colon - Reduced colonisation resistance
The C difficle colonises the gut and releases toxins
The toxins cause mucosal inflammation and damage
When taking a stool sample for enteric infections, what two things are you looking for and why?
Looking for the bacteria antigen and toxin.
Bacteria antigen to make sure the bacteria is present. But positive results might be due to “non-toxic” stains of the bacteria (take make up the normal gut micobiota).
Must look for the toxin also to clarify that the bacteria present is toxic to the gut
Describe the treatments options for Clostidiodes Difficle infection?
- Stop causative antibiotic use
- Use narrow spectrum antibiotic (Metronidazole /Vancomycin) to destroy the C.diff
- Allow the microbiota to recolonise.
- Possibility of the flora to be recolonised by C.Diff. In recurrent C.Diff infection, fecal transplantation may be required
Metronidazole and vancomycin are used in the treatment of Clostridioides difficle infection.
Why is the best mechanism of giving the drug and why?
Metronidazole = Intravenous + Oral
Vancomycin= Oral only
Vancomycin must be given orally because intravenous vancomycin does not concentrate in the bowel mucosa
What is the most common viral gastroenteritis cause?
Norovirus
Why is norovirus highly transmissible?
Gains entry into the body via the faecal oral route
Low infectious dose approx 10-100. i.e. it does not require high numbers of organisms to cause the infection
Very stable in the environment e.g. can survive in temperatues above 60.
One technique to reduce transmission of infection is to use soap and water instead of alcohol gel.
Which infective organisms is this important in protecting against?
Norovirus because the norovirus organisms are highly stable
What is often the best indicator of aetiology for enteric infections?
History
What are the normal treatment options for enteric infections?
Rehydration
Antibiotics rarely indicated (self limiting)
