(23) Gastroenteritis Flashcards
Normal flora organism density in the GIT varies. How many organisms are in the stomach?
10^3-10^6
Normal flora organism density in the GIT varies. How many organisms are in the small bowel?
10^5-10^7
Normal flora organism density in the GIT varies. How many organisms are in the large bowel?
10^9-10^11
The faecal flora has been estimated to have a metabolic capacity equal to what?
That of the liver
What type of bacteria makes up most of the commensal flora of the gut?
Obligate anaerobic bacteria (cannot survive in presence of bacteria) e.g bacteroides
By how much do obligate anaerobes outnumber the facultatively anaerobic coliforms such as E.coli (commensal flora of the gut)?
By at least 100:1
Give an example of a facultative anaerobe in the gut (can survive in but does not need oxygen)
Escherichia coli (gram neg bacilli)
Enterococcus faecalis (gram pos cocci)
Commensal flora of the gut have many beneficial effects. Give examples
- metabolism
- colonisation resistance
- antibody induction
What may have a profound effects on the composition of gut flora?
Diet eg. bottle-fed vs. breast-fed babies
Variation can later predispose to certain infections
Give 2 examples of obligate anaerobes in the gut
Bacteriodes sp. (gram neg bacilli)
Clostridium perfringens (gram pos bacilli)
What are the most common types of bacteria making up the commensal flora of the gut?
- bacteroides
- prevotella
It is very difficult to identify pathogenic organisms from commensal flora in the gut. Give one example why
Many commensals can sometimes cause disease eg. E. coli
How common is diarrhoeal disease?
- second leading cause of death in children under 5
- kills around 760,000 children under 5 each year
- 1.7 billions cases every year globally
Diarrhoea is the leading cause of what in children under 5?
Malnutrition
Diarrhoeal disease is often associated with what?
Travel
Change in environment - change diet - affect normal flora
What are the common BACTERIAL causes of diarrhoeal disease?
- salmonella
- shigella
- E.coli
- campylobacter
- vibrio cholerae
- clostridium difficile
- staph aureus
- bacillus cereus
What are the common PARASITIC (protozoa) causes of diarrhoeal disease?
- entamoeba hist.
- giardia lamblia
- cryptosporidium
What are the common causes of VIRAL diarrhoeal disease?
- norovirus
- rotavirus
The main causes of diarrhoeal disease can come under which 4 categories?
- bacterial
- parasitic
- viral
- non-infective
How has the number of outbreaks of food borne disease in England and Wales changed since 1992?
Decreased
The biggest proportion of food borne disease each year is due to what?
Salmonella spp.
How has the number of outbreaks of non-foodborne disease changed in England and Wales since 1992 ?
Unsteady, lots of peaks and trophy
But increased overall
Outbreaks of non-foodborne disease is associated with what?
Recreational water (swimming pools, lakes etc)
Animals (zoos, farmers, poor hand hygiene)
What are the main causes of non-foodborne disease?
- cryptosporidium spp.
- VTEC 0157 causes have increased significantly since 1992
Describe the typical presenting complaint of diarrhoeal disease
- acute onset
- vomiting
- diarrhoea (frequency, mucous, blood)
- abdominal pain
- systemic effects eg. fever
Give some complications associated with diarrhoeal disease
- dehydration
- toxic megacolon
- renal failure
- Guillain-Barre syndrome
- haemolytic uraemic syndrome
- salmonella (disseminate and cause infections elsewhere)
What is Gullain-Barre syndrome and which bacterial infection is it associated with?
Autoimmune syndrome against part of peripheral nervous system
Associated with campylobacter infections
What 3 main investigations would you do in a presenting complaint of diarrhoeal disease?
- bloods
- abdominal x-ray (if severe)
- stool sample
Which blood tests would you do as part of investigations?
- FBC
- U&E
- CRP
- blood cultures (for infection that has disseminated)
What would you need/what would you do with a stool, sample as part of investigations?
- ova, parasites and cysts (OCP)
- microscopy, culture and sensitivity (MC&S)
- clostridium difficile toxin (CDT)
- viral PCR
What is the most common cause of gut infection in England and Wales?
Norovirus
viral gastroenteritis
What type of virus is norovirus?
SRSV (small round structured virus)
Norwalk-like virus
How many cases of norovirus viral gastroenteritis are there in England every year?
About 600,000 - 1 million
Hence far more common than other well-known gut infections such as salmonella and campylobacter
What is norovirus disease known as and why?
Winter vomiting disease
Massive peaks during the winter months
Why is viral gastroenteritis so contagious?
Symptoms include diarrhoea and vomiting - AEROSOLS
Low infective dose, lasts on surfaces in the environment (very successful pathogen!)
How long does viral gastroenteritis illness last?
Illness lasts for 24-48 hours - no specific treatment
How can you manage viral gastroenteritis?
Let the illness take its course, drink lots of water to prevent dehydration
No specific treatment
How can spread of viral gastroenteritis be controlled/prevented?
Stay away from work
Good hygiene and hand washing
Give the 2 main causes of parasitic gastroenteritis
- cryptosporidium
- giardia
- entamoeba
(amongst others)
Cryptosporidium is predominantly spread by what?
Cryptosporidiosis = mainly waterborne disease
- contaminated drinking water
- swimming pools
- water features
- natural waters
- animal and human contact
- other routes
Cryptosporidium oocysts are resistant to what?
Chlorine based disinfectants
Cryptosporidium infections in the 2nd half of the year (summer) are predominantly what?
C. hominis
Thought to be related to foreign travel and swimming pools
The largest outbreak of food borne cryptosporidiosis was in Yorkshire in 2012. What caused in?
Cryptosporidium parvum
Linked to bagged salad
Cryptosporidium infection is most common in who?
Young children
What is the main symptom of cryptosporidum infection and what is the treatment?
Watery diarrhoea
No specific treatment
What are the two main mechanisms that bacteria use in bacterial gastroenteritis?
- enterotoxin production
- adherence
Which bacteria use enterotoxin production as a mechanism of infection in gastro-enteritis?
- vibrio cholerae
- escherichia coli
- clostridium perfringens
- staphylococcus aureus
- bacillus cereus
- clostridium difficile
Which bacteria use adherence as a mechanism of infection in gastroenteritis?
- shigella sonnei/flexneri
- escherichia coli
- campylobacter jejuni
- salmonellae
What are the 3 different types of E. coli based on their mechanism of infection?
- entertoxigenic (ETEC)
- verotoxigenic (VTEC)
- entertoadherent (EAEC)
What is the most common cause of bacterial gastroenteritis in England/Wales?
Campylobacter
Undercooked meat
The spores of which bacteria can survive cooking?
- clostridium perfringens
- bacillus cereus
Name 5 different types of E. coli
- EHEC/VTEC = enterohaemorrhagic. Colitis/HUS
- ETEC = enterotoxigenic. Travellers’ diarrhoea
- EAggEC = enteroaggregative. Travellers’ diarrhoea
- EIEC = enteroinvasive. Dysentery like
- EPEC = enteropathgenic. Childhood diarrhoea
What strain of E. coli was there an outbreak of in the UK in 2011?
E. coli 0157
What type of E. coli is E. coli 0157?
- enterohaemorrhagic
- VTEC
- shiga-like toxin producing
When was the first outbreak of E. coli 057?
1982, USA
What is the virulence factor of E. coli 0157?
Shiga toxin (acts on red blood cells)
What is the major source of E. coli 057?
Cattle
About 10-15% of E. coli 057 patients develop what?
Haemolytic uraemic syndrome (HUS)
What is the mechanism of action of the E. coli enterotoxin?
- activated G protein
- increased levels of cAMP
- activated ion channels
- overexcrete chloride ions
- water follows out of cells into bowel by osmosis
- massive outpouring of fluid = severe diarrhoea and massive dehydration
Why can killing E. coli with antibiotics make disease worse?
Killing bacteria = release more toxin = makes disease worse
What was the sanitation in Haiti like before earthquake?
12% had piped water
17% had functioning sewage system
What disease outbreak was there in Haiti post-earthquake (surprisingly)
Cholera
Largest outbreak in recent years
CDC “cholera is unlikely to occur, as it is absent in the Caribbean”
How did cholera occur in Haiti despite it being absent in the Caribbean?
Result of introduction, through human activity, of a V. cholerae strain from a distant geographic source
Likely from UN aid workers
Name 4 types of salmonella (salmonella is the genus and has loads of different strains)
- S. typhi
- S. paratyphi
- S. enteritidis
- S. typhimurium
What is the difference between typhoidal and non-typhoidal salmonella?
Typhoidal = able to disseminate, likely to invade cells outside of the GIT, fevers etc
Non-typhoidal = Stays in the GIT
Does salmonella use toxins to infect?
No, it is the bacteria itself that causes problems
Why are antibiotics generally avoided in gastro-enteritis treatment?
- may increase duration of salmonella carriage
- may worse E. coli HUS (release a large amount of toxin as they die)
Antibiotics are generally avoided in gastroenteritis treatment except…
- in very young and very old
- campylobacter (prolonged or severe symptoms)
- invasion (eg. positive blood cultures)
Antibiotic-associated diarrhoea occurs in how many patients?
5-30% patients during, or up to, 2 months post-treatment (diarrhoea as side effect of antibiotics)
(particularly broad-spectrum antibiotics)
Why does antibiotic-associated diarrhoea occur?
Disruption of gut microflora
- change in metabolism (carbohydrates/bile acids)
- overgrowth of pathogenic organisms
What are the symptoms of antibiotic-associtaed diarrhoea?
Range from mild diarrhoea to pseudomembranous colitis
- toxic megacolon
- bowel perforation
- septic shock
Which organisms are associated with antibiotic-associated diarrhoea?
- clostridium difficile (10-25% AAD)
- C. perfringens
- S. aureus
- Candida spp.
- klebsiella spp.
- salmonella spp.
Give a particular risk factor of C. difficile diarrhoea
Old age
80% of cases are in patients over the age of 65
How has the number of reports of C. diff changed since 1982?
Increased gradually and significantly
Associated with antibiotic use
There has been emergence of a new strain of C. diff which is associated with 2.5-3.5-fold increase in death rate. What is the new strain?
CD 027/nap1
Which antibiotics are associated with a HIGH risk of CDI (C. diff infection)?
- cephalosporins
- clindamycin
Which antibiotics are associated with a MEDIUM risk of CDI (C. diff infection)?
- ampicillin/amoxycillin
- co-trimoxazole
- macrolides
- fluoroquinolones
Which antibiotics are associated with LOW risk of CDI (C. diff infection)?
- aminoglycosides
- metronidazole
- anti-pseudomonal penicillins
- b-lactamse inhibitor
- tetracyclines
- rifampicin
- vancomycin
CD 027 is particularly resistant to which antibiotic?
Fluoroquinolones - so these antibiotics can drive 027 infection
What are the CDI key control measures?
- early warning system to identify changes in local epidemiology
- reduce risk of transmission
- early isolation/cohorting of patients with diarrhoea
- environmental cleaning, chlorine
- hand hygiene, soap and water
- examine/optimise/reduce overall antibiotic use
- limit high risk agents in high risk patients
- feedback CDI and antibiotic data on a regular basis
How have the CDI rates in England changed within the period 2007-2010?
Decreased so the control measures are working but it is still a problem
Hospitals get fined for their C diff cases
What is the current CDI therapy?
Oral metronidazole/oral vancomycin
Vanc is superior in severe CDI
The current CDI therapy is oral metronidazole/oral vancomycin. There is relapse in how many patients?
> 20%
With treatment, how long does it take until full resolution of diarrhoea in C diff?
Mean 3-5 days
Vancomycin and metronidazole (CDI therapy) use is a risk for what?
VRE selection
Potential for emergence of resistance to vancomycin/metronidazole in C. difficile
What is a new treatment for CDI?
Oral fidaxomicin (very expensive!)
What was the result of a trial investigating the efficacy of faecal transplant for C. diff infection?
Resolution of diarrhoea with no relapse for 10 weeks
Restores protective effect of gut flora - breaks repetitive cycle for antibiotics
81% recovered
27% and 31% of patients receiving vancomycin only recovered
What did patients show after faecal transplant?
Patients showed increased diversity in colonic microflora, similar to that of healthy donor
